Re: [PATCH 2/2] ext4: Fix potential uas-after-free about sbi->s_mmp_tsk when kmmpd kthread exit before set sbi->s_mmp_tsk
From: Andreas Dilger <hidden>
Date: 2021-07-06 00:44:32
Also in:
lkml
On Jun 29, 2021, at 8:36 AM, Ye Bin [off-list ref] wrote:
Now sbi->s_mmp_tsk is created with kthread_run, then kmmpd maybe
already running and even exit as exception. Even though we set
sbi->s_mmp_tsk with NULL before kmmpd kthread exit, but
"sbi->s_mmp_tsk=kthread_run(XX)" may set after set with NULL.
mount kmmpd
| |
|-call kthread_run |
| |-kmmpd runing
| |-kmmpd exit sbi->s_mmp_tsk=NULL
| |
|-kthread_run return |
| and set sbi->s_mmp_tsk |
| |
|-then we get wild ptr"sbi->s_mmp_tsk" and later trigger UAF
This patch is base on previous "ext4: Fix use-after-free about sbi->s_mmp_tsk".
Previous patch ensure kmmpd kthread exit by itself will set sbi->s_mmp_tsk with
NULL. We can create kthread first, and then wakeup kmmpd kthread later.
Signed-off-by: Ye Bin <redacted>Please note minor typo in the patch subject, should be "use-after-free". Reviewed-by: Andreas Dilger <redacted>
quoted hunk ↗ jump to hunk
--- fs/ext4/mmp.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c index fc18a8c205c7..6ec1ea182cc0 100644 --- a/fs/ext4/mmp.c +++ b/fs/ext4/mmp.c@@ -394,16 +394,18 @@ int ext4_multi_mount_protect(struct super_block *sb,/* * Start a kernel thread to update the MMP block periodically. */ - EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, sb, "kmmpd-%.*s", - (int)sizeof(mmp->mmp_bdevname), - bdevname(bh->b_bdev, - mmp->mmp_bdevname)); + EXT4_SB(sb)->s_mmp_tsk = kthread_create(kmmpd, sb, "kmmpd-%.*s", + (int)sizeof(mmp->mmp_bdevname), + bdevname(bh->b_bdev, + mmp->mmp_bdevname)); + if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) { EXT4_SB(sb)->s_mmp_tsk = NULL; ext4_warning(sb, "Unable to create kmmpd thread for %s.", sb->s_id); goto failed; } + wake_up_process(EXT4_SB(sb)->s_mmp_tsk); return 0; -- 2.31.1
Cheers, Andreas
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