[SRU][N][PATCH 0/1] CVE-2024-42271

[Koichiro Den]

[Impact]

net/iucv: fix use after free in iucv_sock_close()

iucv_sever_path() is called from process context and from bh context.
iucv->path is used as indicator whether somebody else is taking care of
severing the path (or it is already removed / never existed).
This needs to be done with atomic compare and swap, otherwise there is a
small window where iucv_sock_close() will try to work with a path that has
already been severed and freed by iucv_callback_connrej() called by
iucv_tasklet_fn().

Example:
[452744.123844] Call Trace:
[452744.123845] ([<0000001e87f03880>] 0x1e87f03880)
[452744.123966]  [<00000000d593001e>] iucv_path_sever+0x96/0x138
[452744.124330]  [<000003ff801ddbca>] iucv_sever_path+0xc2/0xd0 [af_iucv]
[452744.124336]  [<000003ff801e01b6>] iucv_sock_close+0xa6/0x310 [af_iucv]
[452744.124341]  [<000003ff801e08cc>] iucv_sock_release+0x3c/0xd0 [af_iucv]
[452744.124345]  [<00000000d574794e>] __sock_release+0x5e/0xe8
[452744.124815]  [<00000000d5747a0c>] sock_close+0x34/0x48
[452744.124820]  [<00000000d5421642>] __fput+0xba/0x268
[452744.124826]  [<00000000d51b382c>] task_work_run+0xbc/0xf0
[452744.124832]  [<00000000d5145710>] do_notify_resume+0x88/0x90
[452744.124841]  [<00000000d5978096>] system_call+0xe2/0x2c8
[452744.125319] Last Breaking-Event-Address:
[452744.125321]  [<00000000d5930018>] iucv_path_sever+0x90/0x138
[452744.125324]
[452744.125325] Kernel panic - not syncing: Fatal exception in interrupt

Note that bh_lock_sock() is not serializing the tasklet context against
process context, because the check for sock_owned_by_user() and
corresponding handling is missing.

Ideas for a future clean-up patch:
A) Correct usage of bh_lock_sock() in tasklet context, as described in
Link: https://lore.kernel.org/netdev/1280155406.2899.407.camel@edumazet-laptop/
Re-enqueue, if needed. This may require adding return values to the
tasklet functions and thus changes to all users of iucv.

B) Change iucv tasklet into worker and use only lock_sock() in af_iucv.

[Fix]

Noble:  Clean cherry-pick
Jammy:  fixed via stable
Focal:  fixed via stable
Bionic: fix sent to esm ML
Xenial: fix sent to esm ML
Trusty: won't fix

[Test Case]

Compile and boot tested.

af_iucv module load tested on Noble s390x qemu instance.

[Where problems could occur]

This fix affects those who use af_iucv on s390x, an issue with this fix
would be visible to the user via unpredicted system behavior or a system
crash.


Alexandra Winter (1):
  net/iucv: fix use after free in iucv_sock_close()

 net/iucv/af_iucv.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

-- 
2.43.0