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Date: Fri, 8 Oct 2021 11:52:46 +0800 From: yebin <yebin10@...wei.com> To: Jan Kara <jack@...e.cz> CC: <tytso@....edu>, <adilger.kernel@...ger.ca>, <linux-ext4@...r.kernel.org>, <linux-kernel@...r.kernel.org> Subject: Re: [PATCH -next v2 4/6] ext4: avoid to re-read mmp check data get from page cache On 2021/10/7 20:44, Jan Kara wrote: > 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 <yebin10@...wei.com> > 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 > Yeah, I will refactor 'read_mmp_block'. >> --- >> 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 >>
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