[PATCH v2] ocfs2: Fix shift-out-of-bounds UBSAN bug in ocfs2_verify_volume()

[qasdev <qasdev00@gmail.com>]

On Mon, Aug 19, 2024 at 10:52:29AM +0800, Joseph Qi wrote:
> 
> 
> On 8/18/24 7:43 PM, Heming Zhao wrote:
> > On 8/16/24 21:41, qasdev wrote:
> >>  From ad1ca2fd2ecf4eb7ec2c76fcbbf34639f0ad87ca Mon Sep 17 00:00:00 2001
> >> From: Qasim Ijaz <qasdev00@gmail.com>
> >> Date: Fri, 16 Aug 2024 02:30:25 +0100
> >> Subject: [PATCH] ocfs2: Fix shift-out-of-bounds UBSAN bug in
> >>   ocfs2_verify_volume()
> >>
> 
> The above should be eliminated from patch body. 
> 
> >> This patch addresses a shift-out-of-bounds error in the
> >> ocfs2_verify_volume() function, identified by UBSAN. The bug was triggered
> >> by an invalid s_clustersize_bits value (e.g., 1548), which caused the
> >> expression "1 << le32_to_cpu(di->id2.i_super.s_clustersize_bits)"
> >> to exceed the limits of a 32-bit integer,
> >> leading to an out-of-bounds shift.
> >>
> >> Reported-by: syzbot <syzbot+f3fff775402751ebb471@syzkaller.appspotmail.com>
> >> Closes: https://syzkaller.appspot.com/bug?extid=f3fff775402751ebb471
> >> Tested-by: syzbot <syzbot+f3fff775402751ebb471@syzkaller.appspotmail.com>
> >> Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
> >> ---
> >>   fs/ocfs2/super.c | 8 ++++++--
> >>   1 file changed, 6 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
> >> index afee70125ae3..1e43cdca7f40 100644
> >> --- a/fs/ocfs2/super.c
> >> +++ b/fs/ocfs2/super.c
> >> @@ -2357,8 +2357,12 @@ static int ocfs2_verify_volume(struct ocfs2_dinode *di,
> >>                    (unsigned long long)bh->b_blocknr);
> >>           } else if (le32_to_cpu(di->id2.i_super.s_clustersize_bits) < 12 ||
> >>                   le32_to_cpu(di->id2.i_super.s_clustersize_bits) > 20) {
> >> -            mlog(ML_ERROR, "bad cluster size found: %u\n",
> >> -                 1 << le32_to_cpu(di->id2.i_super.s_clustersize_bits));
> >> +            if (le32_to_cpu(di->id2.i_super.s_clustersize_bits) < 32)
> >> +                mlog(ML_ERROR, "bad cluster size found: %u\n",
> >> +                     1 << le32_to_cpu(di->id2.i_super.s_clustersize_bits));
> >> +            else
> >> +                mlog(ML_ERROR, "invalid cluster size bit value: %u\n",
> >> +                     le32_to_cpu(di->id2.i_super.s_clustersize_bits));
> > 
> > I prefer to use concise code to fix the error.
> > Do you like below code?
> > -        mlog(ML_ERROR, "bad cluster size found: %u\n",
> > -                 1 << le32_to_cpu(di->id2.i_super.s_clustersize_bits));
> > +        mlog(ML_ERROR, "bad cluster size bit found: %u\n",
> > +                 le32_to_cpu(di->id2.i_super.s_clustersize_bits));
> > 
> 
> Agree. qasdev, Could you please update and send v2?
> 
> Thanks,
> Joseph

Thanks for the feedback. After considering the input, I've refined the patch 
to make it more concise. I've updated the patch and included it below:


This patch addresses a shift-out-of-bounds error in the 
ocfs2_verify_volume() function, identified by UBSAN. The bug was triggered 
by an invalid s_clustersize_bits value (e.g., 1548), which caused the 
expression "1 << le32_to_cpu(di->id2.i_super.s_clustersize_bits)" 
to exceed the limits of a 32-bit integer, 
leading to an out-of-bounds shift.

Reported-by: syzbot <syzbot+f3fff775402751ebb471@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=f3fff775402751ebb471
Tested-by: syzbot <syzbot+f3fff775402751ebb471@syzkaller.appspotmail.com>
Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
---
 fs/ocfs2/super.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
index afee70125ae3..b704983b2112 100644
--- a/fs/ocfs2/super.c
+++ b/fs/ocfs2/super.c
@@ -2357,8 +2357,8 @@ static int ocfs2_verify_volume(struct ocfs2_dinode *di,
                     (unsigned long long)bh->b_blocknr);
             } else if (le32_to_cpu(di->id2.i_super.s_clustersize_bits) < 12 ||
                     le32_to_cpu(di->id2.i_super.s_clustersize_bits) > 20) {
-                   mlog(ML_ERROR, "bad cluster size found: %u\n",
-                        1 << le32_to_cpu(di->id2.i_super.s_clustersize_bits));
+                   mlog(ML_ERROR, "bad cluster size bit found: %u\n",
+                        le32_to_cpu(di->id2.i_super.s_clustersize_bits));
             } else if (!le64_to_cpu(di->id2.i_super.s_root_blkno)) {
                     mlog(ML_ERROR, "bad root_blkno: 0\n");
             } else if (!le64_to_cpu(di->id2.i_super.s_system_dir_blkno)) {
-- 
2.30.2