linux-kernel - Re: [PATCH] ocfs2: remove unreasonable unlock

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Message-ID: <20240820055928.580684-1-lizhi.xu@windriver.com>
Date: Tue, 20 Aug 2024 13:59:28 +0800
From: Lizhi Xu <lizhi.xu@...driver.com>
To: <heming.zhao@...e.com>
CC: <jlbec@...lplan.org>, <joseph.qi@...ux.alibaba.com>,
        <linux-kernel@...r.kernel.org>, <lizhi.xu@...driver.com>,
        <mark@...heh.com>, <ocfs2-devel@...ts.linux.dev>,
        <syzbot+ab134185af9ef88dfed5@...kaller.appspotmail.com>,
        <syzkaller-bugs@...glegroups.com>
Subject: Re: [PATCH] ocfs2: remove unreasonable unlock

On Tue, 20 Aug 2024 12:04:39 +0800, Heming wrote:
> > There was a lock release before exiting, so remove the unreasonable unlock.
> >
> > Reported-and-tested-by: syzbot+ab134185af9ef88dfed5@...kaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=ab134185af9ef88dfed5
> > Signed-off-by: Lizhi Xu <lizhi.xu@...driver.com>
> > ---
> >   fs/ocfs2/buffer_head_io.c | 1 -
> >   1 file changed, 1 deletion(-)
> >
> > diff --git a/fs/ocfs2/buffer_head_io.c b/fs/ocfs2/buffer_head_io.c
> > index cdb9b9bdea1f..e62c7e1de4eb 100644
> > --- a/fs/ocfs2/buffer_head_io.c
> > +++ b/fs/ocfs2/buffer_head_io.c
> > @@ -235,7 +235,6 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
> >   		if (bhs[i] == NULL) {
> >   			bhs[i] = sb_getblk(sb, block++);
> >   			if (bhs[i] == NULL) {
> > -				ocfs2_metadata_cache_io_unlock(ci);
> >   				status = -ENOMEM;
> >   				mlog_errno(status);
> >   				/* Don't forget to put previous bh! */
> 
> The fix looks good to me. However, I found another issue in this function.
> 
> In the for-loop after the 'read_failure' label, the condition
> '(bh == NULL) && flags includes OCFS2_BH_READAHEAD' is missing.
> When this contidion is true, this for-loop will call ocfs2_set_buffer_uptodate(ci, bh),
> which then triggers a NULL pointer access error.
> 
> If you agree with my analysis, please add the new fix and send a v2 patch.
I agree with your analysis conclusion, but this is not the same issue
as the current one, so I will split it into two patches. 
The first patch fixes the unbalanced lock issue, and the second patch will
be used to fix the UAF problem of BH.

BR,
Lizhi