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Date: Tue, 29 Jun 2021 22:36:03 +0800 From: Ye Bin <yebin10@...wei.com> To: <tytso@....edu>, <adilger.kernel@...ger.ca>, <linux-ext4@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <jack@...e.cz> CC: Ye Bin <yebin10@...wei.com> Subject: [PATCH 2/2] ext4: Fix potential uas-after-free about sbi->s_mmp_tsk when kmmpd kthread exit before set sbi->s_mmp_tsk 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 <yebin10@...wei.com> --- 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
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