Commit 0ce160c5 authored by Xiaxi Shen's avatar Xiaxi Shen Committed by Theodore Ts'o
Browse files

ext4: fix timer use-after-free on failed mount 



Syzbot has found an ODEBUG bug in ext4_fill_super

The del_timer_sync function cancels the s_err_report timer,
which reminds about filesystem errors daily. We should
guarantee the timer is no longer active before kfree(sbi).

When filesystem mounting fails, the flow goes to failed_mount3,
where an error occurs when ext4_stop_mmpd is called, causing
a read I/O failure. This triggers the ext4_handle_error function
that ultimately re-arms the timer,
leaving the s_err_report timer active before kfree(sbi) is called.

Fix the issue by canceling the s_err_report timer after calling ext4_stop_mmpd.

Signed-off-by: default avatarXiaxi Shen <shenxiaxi26@gmail.com>
Reported-and-tested-by: default avatar <syzbot+59e0101c430934bc9a36@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=59e0101c430934bc9a36
Link: https://patch.msgid.link/20240715043336.98097-1-shenxiaxi26@gmail.com


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
parent bd8daa77

fs/ext4/super.c

+1 −1
Original line number Diff line number Diff line
@@ -5621,8 +5621,8 @@ failed_mount8: __maybe_unused 
failed_mount3:

	/* flush s_sb_upd_work before sbi destroy */

	flush_work(&sbi->s_sb_upd_work);

	del_timer_sync(&sbi->s_err_report);

	ext4_stop_mmpd(sbi);

	del_timer_sync(&sbi->s_err_report);

	ext4_group_desc_free(sbi);

failed_mount:

	if (sbi->s_chksum_driver)