Re: [PATCH -next v2 4/6] ext4: avoid to re-read mmp check data get from page cache
From: Jan Kara <jack@suse.cz>
Date: 2021-10-07 12:44:29
Also in:
lkml
On Sat 11-09-21 17:00:57, Ye Bin wrote:
As call read_mmp_block pass bh_check which value is NULL, then call sb_getblk to get buffer_head. But mmp_block's buffer_head is already exist which also is uptodate. Lead to compare the same data. Signed-off-by: Ye Bin <redacted>
This looks good, except that read_mmp_block() also releases bh it is passed in case of error. So it can free buffer head which is still referenced from EXT4_SB(sb)->s_mmp_bh and cause use-after-free issues. I guess I would just get rid of sb_getblk() in read_mmp_block() and always expect valid bh passed. The only place that passes NULL bh after this patch is one case in ext4_multi_mount_protect() and that can call sb_getblk() on its own. That way we can also simplify read_mmp_block() prototype to: static int read_mmp_block(struct super_block *sb, struct buffer_head *bh); Honza
quoted hunk ↗ jump to hunk
--- fs/ext4/mmp.c | 17 ++++++----------- 1 file changed, 6 insertions(+), 11 deletions(-)diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c index 4433fe7e9e86..007bde3c12b8 100644 --- a/fs/ext4/mmp.c +++ b/fs/ext4/mmp.c@@ -213,10 +213,7 @@ static int kmmpd(void *data) * we need to check if the MMP block is as we write it. */ if (jiffies - last_check_time > mmp_check_interval * HZ) { - struct buffer_head *bh_check = NULL; - struct mmp_struct *mmp_check; - - retval = read_mmp_block(sb, &bh_check, mmp_block); + retval = read_mmp_block(sb, &bh, mmp_block); if (retval) { ext4_error_err(sb, -retval, "error reading MMP data: %d",@@ -224,20 +221,18 @@ static int kmmpd(void *data) goto wait_to_exit; } - mmp_check = (struct mmp_struct *)(bh_check->b_data); - if (seq != mmp_check->mmp_seq || - memcmp(nodename, mmp_check->mmp_nodename, - sizeof(mmp->mmp_nodename))) { - dump_mmp_msg(sb, mmp_check, + mmp = (struct mmp_struct *)(bh->b_data); + if (seq != le32_to_cpu(mmp->mmp_seq) || + memcmp(nodename, mmp->mmp_nodename, + sizeof(nodename))) { + dump_mmp_msg(sb, mmp, "Error while updating MMP info. " "The filesystem seems to have been" " multiply mounted."); ext4_error_err(sb, EBUSY, "abort"); - put_bh(bh_check); retval = -EBUSY; goto wait_to_exit; } - put_bh(bh_check); last_check_time = jiffies; }-- 2.31.1
-- Jan Kara [off-list ref] SUSE Labs, CR