This is a note to let you know that I've just added the patch titled
scsi: sg: Fix slab-use-after-free read in sg_release()
to the 6.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
scsi-sg-fix-slab-use-after-free-read-in-sg_release.patch
and it can be found in the queue-6.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 0345c3f320c8d81c6f231d49996da79259dcd88b
Author: Suraj Sonawane <surajsonawane0215@xxxxxxxxx>
Date: Wed Nov 20 18:29:44 2024 +0530
scsi: sg: Fix slab-use-after-free read in sg_release()
[ Upstream commit f10593ad9bc36921f623361c9e3dd96bd52d85ee ]
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().
Reported-by: syzbot+7efb5850a17ba6ce098b@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=7efb5850a17ba6ce098b
Tested-by: syzbot+7efb5850a17ba6ce098b@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: cc833acbee9d ("sg: O_EXCL and other lock handling")
Signed-off-by: Suraj Sonawane <surajsonawane0215@xxxxxxxxx>
Link: https://lore.kernel.org/r/20241120125944.88095-1-surajsonawane0215@xxxxxxxxx
Reviewed-by: Bart Van Assche <bvanassche@xxxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 84334ab39c810..94127868bedf8 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -386,7 +386,6 @@ sg_release(struct inode *inode, struct file *filp)
SCSI_LOG_TIMEOUT(3, sg_printk(KERN_INFO, sdp, "sg_release\n"));
mutex_lock(&sdp->open_rel_lock);
- kref_put(&sfp->f_ref, sg_remove_sfp);
sdp->open_cnt--;
/* possibly many open()s waiting on exlude clearing, start many;
@@ -398,6 +397,7 @@ sg_release(struct inode *inode, struct file *filp)
wake_up_interruptible(&sdp->open_wait);
}
mutex_unlock(&sdp->open_rel_lock);
+ kref_put(&sfp->f_ref, sg_remove_sfp);
return 0;
}
