proc:prevent /proc/PID/environ access until ready
authorAmulya Y <ayarlagadda@nvidia.com>
Thu, 5 Apr 2018 21:40:20 +0000 (14:40 -0700)
committerWinnie Hsu <whsu@nvidia.com>
Thu, 19 Apr 2018 17:01:00 +0000 (10:01 -0700)
commit1e3475cdd97f5f8b5cde3e5a4780ded2fa108af8
treeff03268f1726995f90493f7fa6c96d97101c55bc
parent6176adbe2d355128e3ac7d03398f750a5807348d
proc:prevent /proc/PID/environ access until ready

If /proc/<PID>/environ gets read before the envp[] array is fully set up
in create_{aout,elf,elf_fdpic,flat}_tables(), we might end up trying to
read more bytes than are actually written, as env_start will already be
set but env_end will still be zero, making the range calculation
underflow, allowing to read beyond the end of what has been written.

Fix this as it is done for /proc/<PID>/cmdline by testing env_end for
zero.  It is, apparently, intentionally set last in create_*_tables().

This bug was found by the PaX size_overflow plugin that detected the
arithmetic underflow of 'this_len = env_end - (env_start + src)' when
env_end is still zero.

The expected consequence is that userland trying to access
/proc/<PID>/environ of a not yet fully set up process may get
inconsistent data as we're in the middle of copying in the environment
variables.

Bug 1823317
Bug 1935735

Change-Id: I38356eb68ffd1294f1f1250fb328bd01a3b37158
Fixes: https://forums.grsecurity.net/viewtopic.php?f=3&t=4363
Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=116461
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Emese Revfy <re.emese@gmail.com>
Cc: Pax Team <pageexec@freemail.hu>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Mateusz Guzik <mguzik@redhat.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Gagan Grover <ggrover@nvidia.com>
Signed-off-by: Amulya Yarlagadda <ayarlagadda@nvidia.com>
Reviewed-on: http://git-master/r/1259930
(cherry picked from commit 78d40f25b8e090782ca6b0c6051020557d373c92)
Reviewed-on: https://git-master.nvidia.com/r/1689554
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Bibek Basu <bbasu@nvidia.com>
Reviewed-by: Winnie Hsu <whsu@nvidia.com>
fs/proc/base.c