CVE-2024-42271

In the Linux kernel, the following vulnerability has been resolved:

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

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.