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[Stephan Springer <launchpad12@xxxxxxx>]

** Changed in: linux (Ubuntu Trusty)
       Status: Incomplete => New

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https://bugs.launchpad.net/bugs/1274349

Title:
  Fix-compat_sys_recvmsg-on-x32-archs

Status in “linux” package in Ubuntu:
  Incomplete
Status in “linux-lts-raring” package in Ubuntu:
  Invalid
Status in “linux-lts-saucy” package in Ubuntu:
  Invalid
Status in “linux” source package in Precise:
  Invalid
Status in “linux-lts-raring” source package in Precise:
  Fix Released
Status in “linux-lts-saucy” source package in Precise:
  Fix Released
Status in “linux” source package in Saucy:
  Fix Released
Status in “linux-lts-raring” source package in Saucy:
  Invalid
Status in “linux-lts-saucy” source package in Saucy:
  Invalid
Status in “linux” source package in Trusty:
  Incomplete
Status in “linux-lts-raring” source package in Trusty:
  Invalid
Status in “linux-lts-saucy” source package in Trusty:
  Invalid

Bug description:
  Reported by pageexec

  asmlinkage long compat_sys_recvmmsg(int fd, struct compat_mmsghdr __user *mmsg,
                                      unsigned int vlen, unsigned int flags,
                                      struct compat_timespec __user *timeout)
  {
          int datagrams;
          struct timespec ktspec;

          if (flags & MSG_CMSG_COMPAT)
                  return -EINVAL;

          if (COMPAT_USE_64BIT_TIME)
                  return __sys_recvmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
                                        flags | MSG_CMSG_COMPAT,
                                        (struct timespec *) timeout);
  /*...*/

  The timeout pointer parameter is provided by userland (hence the
  __user annotation) but for x32 syscalls it's simply cast to a kernel
  pointer and is passed to __sys_recvmmsg which will eventually directly
  dereference it for both reading and writing. Other callers to
  __sys_recvmmsg properly copy from userland to the kernel first.

  The impact is a sort of arbitrary kernel write-where-what primitive by
  unprivileged users where the to-be-written area must contain valid
  timespec data initially (the first 64 bit long field must be positive
  and the second one must be < 1G).

  The bug was introduced by commit
  http://git.kernel.org/linus/ee4fa23c4b (other uses of
  COMPAT_USE_64BIT_TIME seem fine) and should affect all kernels since
  3.4 (and perhaps vendor kernels if they backported x32 support along
  with this code). Note that CONFIG_X86_X32_ABI gets enabled at build
  time and only if CONFIG_X86_X32 is enabled and ld can build x32
  executables.

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