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[Bug 2112614] Re: Regression: After CVE-2025-2312 cifs.upcall can't find credential caches from user env

To: debcrafters-packages@xxxxxxxxxxxxxxxxxxx
From: Matthew Ruffell <2112614@xxxxxxxxxxxxxxxxxx>
Date: Mon, 16 Jun 2025 04:45:29 -0000
Reply-to: Bug 2112614 <2112614@xxxxxxxxxxxxxxxxxx>
Sender: noreply@xxxxxxxxxxxxx
Performing verification for noble:

We are going to perform a series of mounts and check if they work with a 
patched vs unpatched kernel, and make sure all mounts work.

We will start with an unpatched kernel:

ubuntu@noble-dc:~$ uname -rv
6.8.0-60-generic #63-Ubuntu SMP PREEMPT_DYNAMIC Tue Apr 15 19:04:15 UTC 2025

I installed cifs-utils 2:7.0-2.1ubuntu0.1 from -updates.

Let's try and standard uid 1000 user:

ubuntu@noble-dc:~$ kinit Administrator@xxxxxxxxxxxxxxxxxxxx
Password for Administrator@xxxxxxxxxxxxxxxxxxxx: 
Warning: Your password will expire in 25 days on Sat Jul 12 01:54:39 2025
ubuntu@noble-dc:~$ klist
Ticket cache: FILE:/tmp/krb5cc_1000
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 04:22:19  06/16/25 14:22:19  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 04:22:17
ubuntu@noble-dc:~$ sudo mount -t cifs -o cruid=ubuntu,user=ubuntu,sec=krb5i,uid=1000,gid=1000,cred=/tmp/krb5cc_1000 //samba-dc.example.com/demo /mnt/testshare1
ubuntu@noble-dc:~$ mount -l | grep cifs
//samba-dc.example.com/demo on /mnt/testshare1 type cifs (rw,relatime,vers=3.1.1,sec=krb5i,cruid=1000,cache=strict,username=ubuntu,uid=1000,forceuid,gid=1000,forcegid,addr=192.168.122.248,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,rsize=4194304,wsize=4194304,bsize=1048576,retrans=1,echo_interval=60,actimeo=1,closetimeo=1)
$ journalctl -b0
kernel: CIFS: enabling forceuid mount option implicitly because uid= option is specified
kernel: CIFS: enabling forcegid mount option implicitly because gid= option is specified
kernel: CIFS: Attempting to mount //samba-dc.example.com/demo
cifs.upcall[1294]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.248;sec=krb5;u>
cifs.upcall[1295]: ver=2
cifs.upcall[1295]: host=samba-dc.example.com
cifs.upcall[1295]: ip=192.168.122.248
cifs.upcall[1295]: sec=1
cifs.upcall[1295]: uid=1000
cifs.upcall[1295]: creduid=1000
cifs.upcall[1295]: user=ubuntu
cifs.upcall[1295]: pid=1263
cifs.upcall[1294]: upcall_target=app, switching namespaces to application thread
cifs.upcall[1294]: get_cachename_from_process_env: pid == 0
cifs.upcall[1294]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_1000
cifs.upcall[1294]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[1294]: handle_krb5_mech: using native krb5
cifs.upcall[1294]: handle_krb5_mech: obtained service ticket
cifs.upcall[1294]: Exit status 0
ubuntu@noble-dc:~$ sudo umount /mnt/testshare1 

Let's try as a different uid user, e.g. like AD user:

ubuntu@noble-dc:~$ mv /tmp/krb5cc_1000 /tmp/krb5cc_11200
ubuntu@noble-dc:~$ export KRB5CCNAME=/tmp/krb5cc_11200
ubuntu@noble-dc:~$ klist /tmp/krb5cc_11200
Ticket cache: FILE:/tmp/krb5cc_11200
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 04:22:19  06/16/25 14:22:19  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 04:22:17
06/16/25 04:22:27  06/16/25 14:22:19  cifs/samba-dc.example.com@
	renew until 06/17/25 04:22:17
	Ticket server: cifs/samba-dc.example.com@xxxxxxxxxxxxxxxxxxxx
ubuntu@noble-dc:~$ sudo mount -t cifs -o sec=krb5i //samba-dc.example.com/demo /mnt/testshare1
mount error(126): Required key not available
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs) and kernel log messages (dmesg)
ubuntu@noble-dc:~$ mount -l | grep cifs
$ journalctl -b0
kernel: CIFS: Attempting to mount //samba-dc.example.com/demo
cifs.upcall[1392]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.248;sec=krb5;uid=0x0;creduid=0x3e8;user=root;pid=0x563
cifs.upcall[1393]: ver=2
cifs.upcall[1393]: host=samba-dc.example.com
cifs.upcall[1393]: ip=192.168.122.248
cifs.upcall[1393]: sec=1
cifs.upcall[1393]: uid=0
cifs.upcall[1393]: creduid=1000
cifs.upcall[1393]: user=root
cifs.upcall[1393]: pid=1379
cifs.upcall[1392]: upcall_target=app, switching namespaces to application thread
cifs.upcall[1392]: get_cachename_from_process_env: pid == 0
cifs.upcall[1392]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_1000
cifs.upcall[1392]: check_service_ticket_exists: unable to get client principal from cache: No credentials cache found (filename: /tmp/krb5cc_1000)
cifs.upcall[1392]: get_tgt_time: unable to get principal
cifs.upcall[1392]: main: valid TGT is not present in credential cache
cifs.upcall[1392]: krb5_get_init_creds_keytab: -1765328378
cifs.upcall[1392]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[1392]: handle_krb5_mech: using GSS-API
cifs.upcall[1392]: GSS-API error init_sec_context: No credentials were supplied, or the credentials were unavailable or inaccessible
cifs.upcall[1392]: GSS-API error init_sec_context: No Kerberos credentials available (default cache: FILE:/tmp/krb5cc_1000)
cifs.upcall[1392]: handle_krb5_mech: failed to obtain service ticket via GSS (458752)
cifs.upcall[1392]: Unable to obtain service ticket
cifs.upcall[1392]: Exit status 458752
kernel: CIFS: VFS: Verify user has a krb5 ticket and keyutils is installed
kernel: CIFS: VFS: \\samba-dc.example.com Send error in Se

We fail, due to only searching root's env, reproducing the issue.

Let's try as root user:

ubuntu@noble-dc:~$ kdestroy
ubuntu@noble-dc:~$ unset KRB5CCNAME 
ubuntu@noble-dc:~$ sudo -s
root@noble-dc:/home/ubuntu# kinit Administrator@xxxxxxxxxxxxxxxxxxxx
Password for Administrator@xxxxxxxxxxxxxxxxxxxx: 
Warning: Your password will expire in 25 days on Sat Jul 12 01:54:39 2025
root@noble-dc:/home/ubuntu# klist
Ticket cache: FILE:/tmp/krb5cc_0
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 04:24:51  06/16/25 14:24:51  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 04:24:49
root@noble-dc:/home/ubuntu# mount -t cifs -o cruid=root,user=root,sec=krb5i,uid=0,gid=0,cred=/tmp/krb5cc_0 //samba-dc.example.com/demo /mnt/testshare1
root@noble-dc:/home/ubuntu# mount -l | grep cifs
//samba-dc.example.com/demo on /mnt/testshare1 type cifs (rw,relatime,vers=3.1.1,sec=krb5i,cruid=0,cache=strict,username=root,uid=0,forceuid,gid=0,forcegid,addr=192.168.122.248,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,rsize=4194304,wsize=4194304,bsize=1048576,retrans=1,echo_interval=60,actimeo=1,closetimeo=1)
$ journalctl -b0
kernel: CIFS: enabling forceuid mount option implicitly because uid= option is specified
kernel: CIFS: enabling forcegid mount option implicitly because gid= option is specified
kernel: CIFS: Attempting to mount //samba-dc.example.com/demo
cifs.upcall[1418]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.248;sec=krb5;uid=0x0;creduid=0x0;user=root;pid=0x584
cifs.upcall[1419]: ver=2
cifs.upcall[1419]: host=samba-dc.example.com
cifs.upcall[1419]: ip=192.168.122.248
cifs.upcall[1419]: sec=1
cifs.upcall[1419]: uid=0
cifs.upcall[1419]: creduid=0
cifs.upcall[1419]: user=root
cifs.upcall[1419]: pid=1412
cifs.upcall[1418]: upcall_target=app, switching namespaces to application thread
cifs.upcall[1418]: get_cachename_from_process_env: pid == 0
cifs.upcall[1418]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_0
cifs.upcall[1418]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[1418]: handle_krb5_mech: using native krb5
cifs.upcall[1418]: handle_krb5_mech: obtained service ticket
cifs.upcall[1418]: Exit status 0

I then enabled -security-proposed from the following ppa:

https://launchpad.net/~ubuntu-security-
proposed/+archive/ubuntu/ppa/+packages?field.name_filter=cifs-
utils&field.status_filter=published&field.series_filter=

I then installed cifs-utils 2:7.0-2ubuntu0.2

Let's try and standard uid 1000 user:

ubuntu@noble-dc:~$ kinit Administrator@xxxxxxxxxxxxxxxxxxxx
Password for Administrator@xxxxxxxxxxxxxxxxxxxx: 
Warning: Your password will expire in 25 days on Sat Jul 12 01:54:39 2025
ubuntu@noble-dc:~$ klist
Ticket cache: FILE:/tmp/krb5cc_1000
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 04:26:59  06/16/25 14:26:59  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 04:26:56
ubuntu@noble-dc:~$ sudo mount -t cifs -o cruid=ubuntu,user=ubuntu,sec=krb5i,uid=1000,gid=1000,cred=/tmp/krb5cc_1000 //samba-dc.example.com/demo /mnt/testshare1
ubuntu@noble-dc:~$ mount -l | grep cifs
//samba-dc.example.com/demo on /mnt/testshare1 type cifs (rw,relatime,vers=3.1.1,sec=krb5i,cruid=1000,cache=strict,username=ubuntu,uid=1000,forceuid,gid=1000,forcegid,addr=192.168.122.248,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,rsize=4194304,wsize=4194304,bsize=1048576,retrans=1,echo_interval=60,actimeo=1,closetimeo=1)
$ journalctl -b0
kernel: CIFS: enabling forceuid mount option implicitly because uid= option is specified
kernel: CIFS: enabling forcegid mount option implicitly because gid= option is specified
kernel: CIFS: Attempting to mount //samba-dc.example.com/demo
cifs.upcall[2006]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.248;sec=krb5;uid=0x3e8;creduid=0x3e8;user=ubuntu;pid=0x7d0
cifs.upcall[2007]: ver=2
cifs.upcall[2007]: host=samba-dc.example.com
cifs.upcall[2007]: ip=192.168.122.248
cifs.upcall[2007]: sec=1
cifs.upcall[2007]: uid=1000
cifs.upcall[2007]: creduid=1000
cifs.upcall[2007]: user=ubuntu
cifs.upcall[2007]: pid=2000
cifs.upcall[2006]: upcall_target=app, switching namespaces to application thread
cifs.upcall[2006]: get_cachename_from_process_env: pathname=/proc/2000/environ
cifs.upcall[2006]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_1000
cifs.upcall[2006]: main: valid service ticket exists in credential cache
cifs.upcall[2006]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[2006]: handle_krb5_mech: using native krb5
cifs.upcall[2006]: handle_krb5_mech: obtained service ticket
cifs.upcall[2006]: Exit status 0
ubuntu@noble-dc:~$ sudo umount /mnt/testshare1 

Let's try as a different uid user, e.g. like AD user:

ubuntu@noble-dc:~$ export KRB5CCNAME=/tmp/krb5cc_11200
ubuntu@noble-dc:~$ mv /tmp/krb5cc_1000 /tmp/krb5cc_11200
ubuntu@noble-dc:~$ klist /tmp/krb5cc_11200
Ticket cache: FILE:/tmp/krb5cc_11200
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 04:26:59  06/16/25 14:26:59  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 04:26:56
06/16/25 04:27:09  06/16/25 14:26:59  cifs/samba-dc.example.com@
	renew until 06/17/25 04:26:56
	Ticket server: cifs/samba-dc.example.com@xxxxxxxxxxxxxxxxxxxx
ubuntu@noble-dc:~$ sudo mount -t cifs -o sec=krb5i //samba-dc.example.com/demo /mnt/testshare1
ubuntu@noble-dc:~$ mount -l | grep cifs
//samba-dc.example.com/demo on /mnt/testshare1 type cifs (rw,relatime,vers=3.1.1,sec=krb5i,cruid=0,cache=strict,username=root,uid=0,noforceuid,gid=0,noforcegid,addr=192.168.122.248,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,rsize=4194304,wsize=4194304,bsize=1048576,retrans=1,echo_interval=60,actimeo=1,closetimeo=1)
$ journalctl -b0
kernel: CIFS: Attempting to mount //samba-dc.example.com/demo
cifs.upcall[2028]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.248;sec=krb5;uid=0x0;creduid=0x0;user=root;pid=0x7e6
cifs.upcall[2029]: ver=2
cifs.upcall[2029]: host=samba-dc.example.com
cifs.upcall[2029]: ip=192.168.122.248
cifs.upcall[2029]: sec=1
cifs.upcall[2029]: uid=0
cifs.upcall[2029]: creduid=0
cifs.upcall[2029]: user=root
cifs.upcall[2029]: pid=2022
cifs.upcall[2028]: upcall_target=app, switching namespaces to application thread
cifs.upcall[2028]: get_cachename_from_process_env: pid == 0
cifs.upcall[2028]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_0
cifs.upcall[2028]: main: valid service ticket exists in credential cache
cifs.upcall[2028]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[2028]: handle_krb5_mech: using native krb5
cifs.upcall[2028]: handle_krb5_mech: obtained service ticket
cifs.upcall[2028]: Exit status 0

The mount now works correctly, and the regression is fixed.

Let's try as root user:

root@noble-dc:/home/ubuntu# klist
Ticket cache: FILE:/tmp/krb5cc_11200
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 04:26:59  06/16/25 14:26:59  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 04:26:56
06/16/25 04:27:09  06/16/25 14:26:59  cifs/samba-dc.example.com@
	renew until 06/17/25 04:26:56
	Ticket server: cifs/samba-dc.example.com@xxxxxxxxxxxxxxxxxxxx
root@noble-dc:/home/ubuntu# umount /mnt/testshare1
root@noble-dc:/home/ubuntu# mount -t cifs -o cruid=root,user=root,sec=krb5i,uid=0,gid=0,cred=/tmp/krb5cc_0 //samba-dc.example.com/demo /mnt/testshare1
root@noble-dc:/home/ubuntu# mount -l | grep cifs
//samba-dc.example.com/demo on /mnt/testshare1 type cifs (rw,relatime,vers=3.1.1,sec=krb5i,cruid=0,cache=strict,username=root,uid=0,forceuid,gid=0,forcegid,addr=192.168.122.248,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,rsize=4194304,wsize=4194304,bsize=1048576,retrans=1,echo_interval=60,actimeo=1,closetimeo=1)
$ journalctl -b0
kernel: CIFS: enabling forceuid mount option implicitly because uid= option is specified
kernel: CIFS: enabling forcegid mount option implicitly because gid= option is specified
kernel: CIFS: Attempting to mount //samba-dc.example.com/demo
cifs.upcall[2052]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.248;sec=krb5;uid=0x0;creduid=0x0;user=root;pid=0x7fe
cifs.upcall[2053]: ver=2
cifs.upcall[2053]: host=samba-dc.example.com
cifs.upcall[2053]: ip=192.168.122.248
cifs.upcall[2053]: sec=1
cifs.upcall[2053]: uid=0
cifs.upcall[2053]: creduid=0
cifs.upcall[2053]: user=root
cifs.upcall[2053]: pid=2046
cifs.upcall[2052]: upcall_target=app, switching namespaces to application thread
cifs.upcall[2052]: get_cachename_from_process_env: pid == 0
cifs.upcall[2052]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_0
cifs.upcall[2052]: main: valid service ticket exists in credential cache
cifs.upcall[2052]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[2052]: handle_krb5_mech: using native krb5
cifs.upcall[2052]: handle_krb5_mech: obtained service ticket
cifs.upcall[2052]: Exit status 0

Next, we will just do a run with a patched kernel. I enabled -proposed and
installed:

ubuntu@noble-dc:~$ uname -rv
6.8.0-62-generic #65-Ubuntu SMP PREEMPT_DYNAMIC Mon May 19 17:15:03 UTC 2025

We will keep cifs-utils from -security-proposed installed.

Let's try and standard uid 1000 user:

ubuntu@noble-dc:~$ kinit Administrator@xxxxxxxxxxxxxxxxxxxx
Password for Administrator@xxxxxxxxxxxxxxxxxxxx: 
Warning: Your password will expire in 25 days on Sat Jul 12 01:54:39 2025
ubuntu@noble-dc:~$ klist
Ticket cache: FILE:/tmp/krb5cc_1000
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 04:32:50  06/16/25 14:32:50  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 04:32:47
ubuntu@noble-dc:~$ sudo mount -t cifs -o cruid=ubuntu,user=ubuntu,sec=krb5i,uid=1000,gid=1000,cred=/tmp/krb5cc_1000 //samba-dc.example.com/demo /mnt/testshare1
ubuntu@noble-dc:~$ mount -l | grep cifs
//samba-dc.example.com/demo on /mnt/testshare1 type cifs (rw,relatime,vers=3.1.1,sec=krb5i,cruid=1000,cache=strict,upcall_target=app,username=ubuntu,uid=1000,forceuid,gid=1000,forcegid,addr=192.168.122.248,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,rsize=4194304,wsize=4194304,bsize=1048576,retrans=1,echo_interval=60,actimeo=1,closetimeo=1)
$ journalctl -b0
kernel: CIFS: enabling forceuid mount option implicitly because uid= option is specified
kernel: CIFS: enabling forcegid mount option implicitly because gid= option is specified
kernel: CIFS: Attempting to mount //samba-dc.example.com/demo
cifs.upcall[1247]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.248;sec=krb5;uid=0x3e8;creduid=0x3e8;user=ubuntu;pid=0x4db;upcall_target=app
cifs.upcall[1248]: ver=2
cifs.upcall[1248]: host=samba-dc.example.com
cifs.upcall[1248]: ip=192.168.122.248
cifs.upcall[1248]: sec=1
cifs.upcall[1248]: uid=1000
cifs.upcall[1248]: creduid=1000
cifs.upcall[1248]: user=ubuntu
cifs.upcall[1248]: pid=1243
cifs.upcall[1248]: upcall_target=app
cifs.upcall[1247]: upcall_target=app, switching namespaces to application thread
cifs.upcall[1247]: get_cachename_from_process_env: pathname=/proc/1243/environ
cifs.upcall[1247]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_1000
cifs.upcall[1247]: main: valid service ticket exists in credential cache
cifs.upcall[1247]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[1247]: handle_krb5_mech: using native krb5
cifs.upcall[1247]: handle_krb5_mech: obtained service ticket
cifs.upcall[1247]: Exit status 0

Let's try as a different uid user, e.g. like AD user:

ubuntu@noble-dc:~$ export KRB5CCNAME=/tmp/krb5cc_11200
ubuntu@noble-dc:~$ mv /tmp/krb5cc_1000 /tmp/krb5cc_11200
ubuntu@noble-dc:~$ klist
Ticket cache: FILE:/tmp/krb5cc_11200
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 04:32:50  06/16/25 14:32:50  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 04:32:47
06/16/25 04:33:01  06/16/25 14:32:50  cifs/samba-dc.example.com@
	renew until 06/17/25 04:32:47
	Ticket server: cifs/samba-dc.example.com@xxxxxxxxxxxxxxxxxxxx
ubuntu@noble-dc:~$ sudo mount -t cifs -o sec=krb5i //samba-dc.example.com/demo /mnt/testshare1
ubuntu@noble-dc:~$ mount -l | grep cifs
//samba-dc.example.com/demo on /mnt/testshare1 type cifs (rw,relatime,vers=3.1.1,sec=krb5i,cruid=1000,cache=strict,upcall_target=app,username=root,uid=0,noforceuid,gid=0,noforcegid,addr=192.168.122.248,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,rsize=4194304,wsize=4194304,bsize=1048576,retrans=1,echo_interval=60,actimeo=1,closetimeo=1)
$ journalctl -b0
kernel: CIFS: Attempting to mount //samba-dc.example.com/demo
cifs.upcall[1283]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.248;sec=krb5;uid=0x0;creduid=0x3e8;user=root;pid=0x4fa;upcall_target=app
cifs.upcall[1284]: ver=2
cifs.upcall[1284]: host=samba-dc.example.com
cifs.upcall[1284]: ip=192.168.122.248
cifs.upcall[1284]: sec=1
cifs.upcall[1284]: uid=0
cifs.upcall[1284]: creduid=1000
cifs.upcall[1284]: user=root
cifs.upcall[1284]: pid=1274
cifs.upcall[1284]: upcall_target=app
cifs.upcall[1283]: upcall_target=app, switching namespaces to application thread
cifs.upcall[1283]: get_cachename_from_process_env: pathname=/proc/1274/environ
cifs.upcall[1283]: get_cachename_from_process_env: cachename = /tmp/krb5cc_11200
cifs.upcall[1283]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_11200
cifs.upcall[1283]: main: valid service ticket exists in credential cache
cifs.upcall[1283]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[1283]: handle_krb5_mech: using native krb5
cifs.upcall[1283]: handle_krb5_mech: obtained service ticket
cifs.upcall[1283]: Exit status 0

Let's try as root user:

root@noble-dc:/home/ubuntu# kinit Administrator@xxxxxxxxxxxxxxxxxxxx
Password for Administrator@xxxxxxxxxxxxxxxxxxxx: 
Warning: Your password will expire in 25 days on Sat Jul 12 01:54:39 2025
root@noble-dc:/home/ubuntu# klist
Ticket cache: FILE:/tmp/krb5cc_0
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 04:35:58  06/16/25 14:35:58  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 04:35:54
root@noble-dc:/home/ubuntu# mount -t cifs -o cruid=root,user=root,sec=krb5i,uid=0,gid=0,cred=/tmp/krb5cc_0 //samba-dc.example.com/demo /mnt/testshare1
root@noble-dc:/home/ubuntu# mount -l | grep cifs
//samba-dc.example.com/demo on /mnt/testshare1 type cifs (rw,relatime,vers=3.1.1,sec=krb5i,cruid=0,cache=strict,upcall_target=app,username=root,uid=0,forceuid,gid=0,forcegid,addr=192.168.122.248,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,rsize=4194304,wsize=4194304,bsize=1048576,retrans=1,echo_interval=60,actimeo=1,closetimeo=1)
$ journalctl -b0
kernel: CIFS: enabling forceuid mount option implicitly because uid= option is specified
kernel: CIFS: enabling forcegid mount option implicitly because gid= option is specified
kernel: CIFS: Attempting to mount //samba-dc.example.com/demo
cifs.upcall[1312]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.248;sec=krb5;uid=0x0;creduid=0x0;user=root;pid=0x51c;upcall_target=app
cifs.upcall[1313]: ver=2
cifs.upcall[1313]: host=samba-dc.example.com
cifs.upcall[1313]: ip=192.168.122.248
cifs.upcall[1313]: sec=1
cifs.upcall[1313]: uid=0
cifs.upcall[1313]: creduid=0
cifs.upcall[1313]: user=root
cifs.upcall[1313]: pid=1308
cifs.upcall[1313]: upcall_target=app
cifs.upcall[1312]: upcall_target=app, switching namespaces to application thread
cifs.upcall[1312]: get_cachename_from_process_env: pid == 0
cifs.upcall[1312]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_0
cifs.upcall[1312]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[1312]: handle_krb5_mech: using native krb5
cifs.upcall[1312]: handle_krb5_mech: obtained service ticket
cifs.upcall[1312]: Exit status 0

Everything still mounts okay with the cifs-utils package in -security-
proposed.

Happy to mark verified for noble.

** Tags added: verification-done-noble

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You received this bug notification because you are a member of
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https://bugs.launchpad.net/bugs/2112614

Title:
  Regression: After CVE-2025-2312 cifs.upcall can't find credential
  caches from user env

Status in cifs-utils package in Ubuntu:
  Fix Released
Status in cifs-utils source package in Focal:
  Fix Committed
Status in cifs-utils source package in Jammy:
  Fix Committed
Status in cifs-utils source package in Noble:
  Fix Committed
Status in cifs-utils source package in Oracular:
  Fix Committed
Status in cifs-utils source package in Plucky:
  Fix Committed
Status in cifs-utils source package in Questing:
  Fix Released

Bug description:
  [Impact]

  Unfortunately, the release of CVE-2025-2312 caused a minor regression for some
  users of cifs-utils, particularly those with AD users mounting shares from
  non-standard UID numbers that aren't the default 0 or 1000.

  Trying to mount a share with credentials in environment variables like
  $KRB5CCNAME gets messages like:

  $ echo $KRB5CCNAME
  /tmp/krb5cc_11200
  $ sudo mount -t cifs -o sec=krb5i //samba-dc.example.com/demo /mnt/testshare1
  mount error(126): Required key not available
  Refer to the mount.cifs(8) manual page (e.g. man mount.cifs) and kernel log messages (dmesg)

  Affected packages:

  questing: 2:7.3-1
  plucky: 2:7.2-2
  oracular: 2:7.0-2.1ubuntu0.1
  noble: 2:7.0-2ubuntu0.1
  jammy: 2:6.14-1ubuntu0.2
  focal: 2:6.9-1ubuntu0.3

  We changed debian/patches/CVE-2025-2312-1.patch:
  @@ -1384,7 +1423,7 @@
           * look at the environ file.
           */
          env_cachename =
  - get_cachename_from_process_env(env_probe ? arg->pid : 0);
  + get_cachename_from_process_env((env_probe && (arg->upcall_target == UPTARGET_APP)) ? arg->pid : 0);

          rc = setuid(uid);
          if (rc == -1) {

  Unfortunately, we missed the UPTARGET_UNSPECIFIED option.

  The fix from Henrique Carvalho simply sets upcall_target to be UPTARGET_APP
  if UPTARGET_UNSPECIFIED is the current option.

  This affects users who use the non-patched kernels.

  I'm broken, please get me a fix / Workarounds:
  1) You can install the test packages in the [Testcase] section.
  or
  2) You can enable -proposed and install any of the 5.4.0-218-generic, 5.15.0-142-generic, 6.8.0-62-generic or 6.11.0-28-generic kernels.
  or
  3) You can edit the following files:
  /etc/krb5.conf - Add this to [libdefaults]:
      default_ccache_name = /tmp/krb5cc_%{uid}
  /etc/sssd/sssd.conf - Add this to [domain]
      krb5_ccachedir = /tmp
      krb5_ccname_template = FILE:%d/krb5cc_%{uid}
  Ideally restart sssd so sssd-pam can find the kerberos crediental cache again.
      sudo systemctl restart sssd
  or
  4) you can simply downgrade the package to what is in the release pocket.

  [Testcase]

  Follow the entire testcase of https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2099914
  first.

  $ kinit administrator
  Password for administrator@xxxxxxxxxxxxxxxxxxxx:
  Warning: Your password will expire in 36 days on Sat Jul 12 01:54:39 2025
  $ klist
  Ticket cache: FILE:/tmp/krb5cc_1000
  Default principal: administrator@xxxxxxxxxxxxxxxxxxxx

  Valid starting     Expires            Service principal
  06/05/25 21:44:07  06/06/25 07:44:07  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
   renew until 06/06/25 21:44:04

  $ mv /tmp/krb5cc_1000 /tmp/krb5cc_11200
  $ klist /tmp/krb5cc_11200
  Ticket cache: FILE:/tmp/krb5cc_11200
  Default principal: administrator@xxxxxxxxxxxxxxxxxxxx

  Valid starting     Expires            Service principal
  06/05/25 21:44:07  06/06/25 07:44:07  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
   renew until 06/06/25 21:44:04

  $ export KRB5CCNAME=/tmp/krb5cc_11200
  $ sudo mount -t cifs -o sec=krb5i //samba-dc.example.com/demo /mnt/testshare1
  mount error(126): Required key not available
  Refer to the mount.cifs(8) manual page (e.g. man mount.cifs) and kernel log messages (dmesg)

  $ journalctl -b0
  kernel: CIFS: Attempting to mount //samba-dc.example.com/demo
  cifs.upcall[5177]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.248;sec=krb5;uid=0x0;creduid=0x3e8;user=root;pid=0x142c
  cifs.upcall[5178]: ver=2
  cifs.upcall[5178]: host=samba-dc.example.com
  cifs.upcall[5178]: ip=192.168.122.248
  cifs.upcall[5178]: sec=1
  cifs.upcall[5178]: uid=0
  cifs.upcall[5178]: creduid=1000
  cifs.upcall[5178]: user=root
  cifs.upcall[5178]: pid=5164
  cifs.upcall[5177]: upcall_target=app, switching namespaces to application thread
  cifs.upcall[5177]: get_cachename_from_process_env: pid == 0
  cifs.upcall[5177]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_1000
  cifs.upcall[5177]: check_service_ticket_exists: unable to get client principal from cache: No credentials cache found (filename: /tmp/krb5cc_1000)
  cifs.upcall[5177]: get_tgt_time: unable to get principal
  cifs.upcall[5177]: main: valid TGT is not present in credential cache
  cifs.upcall[5177]: krb5_get_init_creds_keytab: -1765328378
  cifs.upcall[5177]: handle_krb5_mech: getting service ticket for samba-dc.example.com
  cifs.upcall[5177]: handle_krb5_mech: using GSS-API
  cifs.upcall[5177]: GSS-API error init_sec_context: No credentials were supplied, or the credentials were unavailable or inaccessible
  cifs.upcall[5177]: GSS-API error init_sec_context: No Kerberos credentials available (default cache: FILE:/tmp/krb5cc_1000)
  cifs.upcall[5177]: handle_krb5_mech: failed to obtain service ticket via GSS (458752)
  cifs.upcall[5177]: Unable to obtain service ticket
  cifs.upcall[5177]: Exit status 458752
  kernel: CIFS: VFS: Verify user has a krb5 ticket and keyutils is installed
  kernel: CIFS: VFS: \\samba-dc.example.com Send error in SessSetup = -126
  kernel: CIFS: VFS: cifs_mount failed w/return code = -126

  If you install the test packages in the following ppa:

  https://launchpad.net/~mruffell/+archive/ubuntu/sf407276-regression-
  test

  Please note this package is NOT SUPPORTED by Canonical, and is for TESTING
  PURPOSES ONLY. ONLY Install in a dedicated test environment.

  Instructions to Install (On a focal, jammy, noble, oracular, plucky system):
  1) sudo add-apt-repository ppa:mruffell/sf407276-regression-test
  2) sudo apt update
  3) sudo apt install cifs-utils
  4) sudo apt-cache policy cifs-utils | grep Installed
  Check for +sf407276v20250531b1

  The share mounts normally as expected.

  [Where problems can occur]

  This is a part of the fix of CVE-2025-2312, and we need to make sure that we
  again, test the following scenarios:

  * patched kernel, patched cifs-utils
  * patched kernel, existing cifs-utils
  * existing kernel, patched cifs-utils

  This time, we really need to spend a bit more time on the unpatched kernel
  scenario, because clearly I wasn't thorough enough.

  If a regression were to occur, it could affect mounting of cifs / smb shares and
  users would not be able to access their data.

  Due to the nature of this bug, there is no secret leakage from
  CVE-2025-2312.

  [Other info]

  This regression was caused in:
  https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2099914

  This has been fixed upstream in cifs-utils 7.4 by:

  commit f4fd27cf60d6431d83ea18b4962aef845f9312bd
  Author: Henrique Carvalho <henrique.carvalho@xxxxxxxx>
  Date: Fri May 30 12:28:14 2025 -0300
  Subject: cifs.upcall: correctly treat UPTARGET_UNSPECIFIED as UPTARGET_APP
  Link: https://git.samba.org/?p=cifs-utils.git;a=commit;h=f4fd27cf60d6431d83ea18b4962aef845f9312bd

  Mailing list link:
  https://lore.kernel.org/linux-cifs/20250530152814.1592508-1-henrique.carvalho@xxxxxxxx/T/

  Note, there is an additional regression caused by:
  https://bugs.launchpad.net/ubuntu/+source/cifs-utils/+bug/2099917
  that is getting fixed in:
  https://bugs.launchpad.net/ubuntu/+source/cifs-utils/+bug/2113906

To manage notifications about this bug go to:
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References

[Bug 2112614] [NEW] Regression: After CVE-2025-2312 cifs.upcall can't find credential caches from user env
From: Matthew Ruffell, 2025-06-06