CVE-2024-56631

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

scsi: sg: Fix slab-use-after-free read in sg_release()

Fix a use-after-free bug in sg_release(), detected by syzbot with KASAN:

BUG: KASAN: slab-use-after-free in lock_release+0x151/0xa30

kernel/locking/lockdep.c:5838

__mutex_unlock_slowpath+0xe2/0x750 kernel/locking/mutex.c:912

sg_release+0x1f4/0x2e0 drivers/scsi/sg.c:407

In sg_release(), the function kref_put(&sfp->f_ref, sg_remove_sfp) is

called before releasing the open_rel_lock mutex. The kref_put() call may

decrement the reference count of sfp to zero, triggering its cleanup

through sg_remove_sfp(). This cleanup includes scheduling deferred work

via sg_remove_sfp_usercontext(), which ultimately frees sfp.

After kref_put(), sg_release() continues to unlock open_rel_lock and may

reference sfp or sdp. If sfp has already been freed, this results in a

slab-use-after-free error.

Move the kref_put(&sfp->f_ref, sg_remove_sfp) call after unlocking the

open_rel_lock mutex. This ensures:

- No references to sfp or sdp occur after the reference count is

decremented.

- Cleanup functions such as sg_remove_sfp() and

sg_remove_sfp_usercontext() can safely execute without impacting the

mutex handling in sg_release().

The fix has been tested and validated by syzbot. This patch closes the

bug reported at the following syzkaller link and ensures proper

sequencing of resource cleanup and mutex operations, eliminating the

risk of use-after-free errors in sg_release().