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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 04:05:33 -0000
Reply-to: Bug 2112614 <2112614@xxxxxxxxxxxxxxxxxx>
Sender: noreply@xxxxxxxxxxxxx
Performing verification for plucky:

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.

For plucky, all kernels are patched, so we are just going to check cifs-utils
with 6.14.0-15-generic.

I installed cifs-utils 2:7.2-2 from -release.

Let's try and standard uid 1000 user:

ubuntu@plucky-dc:~$ kinit Administrator@xxxxxxxxxxxxxxxxxxxx
Password for Administrator@xxxxxxxxxxxxxxxxxxxx: 
Warning: Your password will expire in 38 days on Fri Jul 25 00:23:17 2025
ubuntu@plucky-dc:~$ klist
Ticket cache: FILE:/tmp/krb5cc_1000
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 03:43:53  06/16/25 13:43:53  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 03:43:51
ubuntu@plucky-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@plucky-dc:~$ mount -l
//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=192.168.122.106,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,reparse=nfs,nativesocket,symlink=native,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[2109]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.106;sec=krb5;uid=0x3e8;creduid=0x3e8;user=ubuntu;pid=0x837;upcall_target=app
cifs.upcall[2110]: ver=2
cifs.upcall[2110]: host=samba-dc.example.com
cifs.upcall[2110]: ip=192.168.122.106
cifs.upcall[2110]: sec=1
cifs.upcall[2110]: uid=1000
cifs.upcall[2110]: creduid=1000
cifs.upcall[2110]: user=ubuntu
cifs.upcall[2110]: pid=2103
cifs.upcall[2110]: upcall_target=app
cifs.upcall[2109]: upcall_target=app, switching namespaces to application thread
cifs.upcall[2109]: get_cachename_from_process_env: pathname=/proc/2103/environ
cifs.upcall[2109]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_1000
cifs.upcall[2109]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[2109]: handle_krb5_mech: using native krb5
cifs.upcall[2109]: handle_krb5_mech: obtained service ticket
cifs.upcall[2109]: Exit status 0
ubuntu@plucky-dc:~$ sudo umount /mnt/testshare1 

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

ubuntu@plucky-dc:~$ kinit Administrator@xxxxxxxxxxxxxxxxxxxx
Password for Administrator@xxxxxxxxxxxxxxxxxxxx: 
Warning: Your password will expire in 38 days on Fri Jul 25 00:23:17 2025
ubuntu@plucky-dc:~$ klist
Ticket cache: FILE:/tmp/krb5cc_1000
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 03:36:35  06/16/25 13:36:35  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 03:36:33
ubuntu@plucky-dc:~$ mv /tmp/krb5cc_1000 /tmp/krb5cc_11200
ubuntu@plucky-dc:~$ export KRB5CCNAME=/tmp/krb5cc_11200
ubuntu@plucky-dc:~$ klist /tmp/krb5cc_11200
Ticket cache: FILE:/tmp/krb5cc_11200
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 03:36:35  06/16/25 13:36:35  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 03:36:33
ubuntu@plucky-dc:~$ sudo mount -t cifs -o sec=krb5i //samba-dc.example.com/demo /mnt/testshare1
ubuntu@plucky-dc:~$ mount -l
...
//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=192.168.122.106,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,reparse=nfs,nativesocket,symlink=native,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[2019]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.106;sec=krb5;uid=0x0;creduid=0x3e8;user=root;pid=0x7bd;upcall_target=app
cifs.upcall[2020]: ver=2
cifs.upcall[2020]: host=samba-dc.example.com
cifs.upcall[2020]: ip=192.168.122.106
cifs.upcall[2020]: sec=1
cifs.upcall[2020]: uid=0
cifs.upcall[2020]: creduid=1000
cifs.upcall[2020]: user=root
cifs.upcall[2020]: pid=1981
cifs.upcall[2020]: upcall_target=app
cifs.upcall[2019]: upcall_target=app, switching namespaces to application thread
cifs.upcall[2019]: get_cachename_from_process_env: pathname=/proc/1981/environ
cifs.upcall[2019]: get_cachename_from_process_env: cachename = /tmp/krb5cc_11200
cifs.upcall[2019]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_11200
cifs.upcall[2019]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[2019]: handle_krb5_mech: using native krb5
cifs.upcall[2019]: handle_krb5_mech: obtained service ticket
cifs.upcall[2019]: Exit status 0

Let's try as root user:

root@plucky-dc:/home/ubuntu# kinit Administrator@xxxxxxxxxxxxxxxxxxxx
Password for Administrator@xxxxxxxxxxxxxxxxxxxx: 
Warning: Your password will expire in 38 days on Fri Jul 25 00:23:17 2025
root@plucky-dc:/home/ubuntu# klist
Ticket cache: FILE:/tmp/krb5cc_0
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 03:41:48  06/16/25 13:41:48  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 03:41:45
root@plucky-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@plucky-dc:/home/ubuntu# mount -l
...
//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=192.168.122.106,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,reparse=nfs,nativesocket,symlink=native,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[2087]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.106;sec=krb5;uid=0x0;creduid=0x0;user=root;pid=0x821;upcall_target=app
cifs.upcall[2088]: ver=2
cifs.upcall[2088]: host=samba-dc.example.com
cifs.upcall[2088]: ip=192.168.122.106
cifs.upcall[2088]: sec=1
cifs.upcall[2088]: uid=0
cifs.upcall[2088]: creduid=0
cifs.upcall[2088]: user=root
cifs.upcall[2088]: pid=2081
cifs.upcall[2088]: upcall_target=app
cifs.upcall[2087]: upcall_target=app, switching namespaces to application thread
cifs.upcall[2087]: get_cachename_from_process_env: pid == 0
cifs.upcall[2087]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_0
cifs.upcall[2087]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[2087]: handle_krb5_mech: using native krb5
cifs.upcall[2087]: handle_krb5_mech: obtained service ticket
cifs.upcall[2087]: Exit status 0
root@plucky-dc:/home/ubuntu# umount /mnt/testshare1

Since plucky's kernel always sets UPTARGET_APP, it always works.

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 2:7.2-2ubuntu0.1

Let's try and standard uid 1000 user:

ubuntu@plucky-dc:~$ klist
Ticket cache: FILE:/tmp/krb5cc_1000
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 03:43:53  06/16/25 13:43:53  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 03:43:51
06/16/25 03:44:36  06/16/25 13:43:53  cifs/samba-dc.example.com@
	renew until 06/17/25 03:43:51
	Ticket server: cifs/samba-dc.example.com@xxxxxxxxxxxxxxxxxxxx
ubuntu@plucky-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@plucky-dc:~$ mount -l
//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=192.168.122.106,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,reparse=nfs,nativesocket,symlink=native,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[2284]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.106;sec=krb5;uid=0x3e8;creduid=0x3e8;user=ubuntu;pid=0x8e6;upcall_target=app
cifs.upcall[2285]: ver=2
cifs.upcall[2285]: host=samba-dc.example.com
cifs.upcall[2285]: ip=192.168.122.106
cifs.upcall[2285]: sec=1
cifs.upcall[2285]: uid=1000
cifs.upcall[2285]: creduid=1000
cifs.upcall[2285]: user=ubuntu
cifs.upcall[2285]: pid=2278
cifs.upcall[2285]: upcall_target=app
cifs.upcall[2284]: upcall_target=app, switching namespaces to application thread
cifs.upcall[2284]: get_cachename_from_process_env: pathname=/proc/2278/environ
cifs.upcall[2284]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_1000
cifs.upcall[2284]: main: valid service ticket exists in credential cache
cifs.upcall[2284]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[2284]: handle_krb5_mech: using native krb5
cifs.upcall[2284]: handle_krb5_mech: obtained service ticket
cifs.upcall[2284]: Exit status 0
ubuntu@plucky-dc:~$ sudo umount /mnt/testshare1 

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

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

Valid starting     Expires            Service principal
06/16/25 03:43:53  06/16/25 13:43:53  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 03:43:51
06/16/25 03:44:36  06/16/25 13:43:53  cifs/samba-dc.example.com@
	renew until 06/17/25 03:43:51
	Ticket server: cifs/samba-dc.example.com@xxxxxxxxxxxxxxxxxxxx
ubuntu@plucky-dc:~$ sudo mount -t cifs -o sec=krb5i //samba-dc.example.com/demo /mnt/testshare1
ubuntu@plucky-dc:~$ mount -l
...
//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,noforceuid,gid=0,noforcegid,addr=192.168.122.106,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,reparse=nfs,nativesocket,symlink=native,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[2312]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.106;sec=krb5;uid=0x0;creduid=0x0;user=root;pid=0x902;upcall_target=app
cifs.upcall[2313]: ver=2
cifs.upcall[2313]: host=samba-dc.example.com
cifs.upcall[2313]: ip=192.168.122.106
cifs.upcall[2313]: sec=1
cifs.upcall[2313]: uid=0
cifs.upcall[2313]: creduid=0
cifs.upcall[2313]: user=root
cifs.upcall[2313]: pid=2306
cifs.upcall[2313]: upcall_target=app
cifs.upcall[2312]: upcall_target=app, switching namespaces to application thread
cifs.upcall[2312]: get_cachename_from_process_env: pid == 0
cifs.upcall[2312]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_0
cifs.upcall[2312]: main: valid service ticket exists in credential cache
cifs.upcall[2312]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[2312]: handle_krb5_mech: using native krb5
cifs.upcall[2312]: handle_krb5_mech: obtained service ticket
cifs.upcall[2312]: Exit status 0

Let's try as root user:

root@plucky-dc:/home/ubuntu# klist
Ticket cache: FILE:/tmp/krb5cc_0
Default principal: Administrator@xxxxxxxxxxxxxxxxxxxx

Valid starting     Expires            Service principal
06/16/25 03:41:48  06/16/25 13:41:48  krbtgt/SAMBA-DC.EXAMPLE.COM@xxxxxxxxxxxxxxxxxxxx
	renew until 06/17/25 03:41:45
06/16/25 03:41:58  06/16/25 13:41:48  cifs/samba-dc.example.com@
	renew until 06/17/25 03:41:45
	Ticket server: cifs/samba-dc.example.com@xxxxxxxxxxxxxxxxxxxx
root@plucky-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@plucky-dc:/home/ubuntu# mount -l
...
//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=192.168.122.106,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,reparse=nfs,nativesocket,symlink=native,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[2345]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=samba-dc.example.com;ip4=192.168.122.106;sec=krb5;uid=0x0;creduid=0x0;user=root;pid=0x923;upcall_target=app
cifs.upcall[2346]: ver=2
cifs.upcall[2346]: host=samba-dc.example.com
cifs.upcall[2346]: ip=192.168.122.106
cifs.upcall[2346]: sec=1
cifs.upcall[2346]: uid=0
cifs.upcall[2346]: creduid=0
cifs.upcall[2346]: user=root
cifs.upcall[2346]: pid=2339
cifs.upcall[2346]: upcall_target=app
cifs.upcall[2345]: upcall_target=app, switching namespaces to application thread
cifs.upcall[2345]: get_cachename_from_process_env: pid == 0
cifs.upcall[2345]: get_existing_cc: default ccache is FILE:/tmp/krb5cc_0
cifs.upcall[2345]: main: valid service ticket exists in credential cache
cifs.upcall[2345]: handle_krb5_mech: getting service ticket for samba-dc.example.com
cifs.upcall[2345]: handle_krb5_mech: using native krb5
cifs.upcall[2345]: handle_krb5_mech: obtained service ticket
cifs.upcall[2345]: Exit status 0

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

Happy to mark verified for plucky.

** Tags added: verification-done-plucky

-- 
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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

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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