[PATCH] bcachefs: return err ptr instead of null in read sb clean

[PATCH] bcachefs: return err ptr instead of null in read sb clean

[Diogo Jahchan Koike]

syzbot reported a null-ptr-deref in bch2_fs_start. [0]

When a sb is marked clear but doesn't have a clean section
bch2_read_superblock_clean returns NULL which PTR_ERR_OR_ZERO
lets through, eventually leading to a null ptr dereference down
the line. Adjust read sb clean to return an ERR_PTR indicating the
invalid clean section.

[0] https://syzkaller.appspot.com/bug?extid=1cecc37d87c4286e5543

Reported-by: syzbot+1cecc37d87c4286e5543@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=1cecc37d87c4286e5543
Signed-off-by: Diogo Jahchan Koike <djahchankoike@gmail.com>
---
 fs/bcachefs/sb-clean.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/bcachefs/sb-clean.c b/fs/bcachefs/sb-clean.c
index c57d42bb8d1b..025848a9c4c0 100644
--- a/fs/bcachefs/sb-clean.c
+++ b/fs/bcachefs/sb-clean.c
@@ -155,7 +155,7 @@ struct bch_sb_field_clean *bch2_read_superblock_clean(struct bch_fs *c)
 		SET_BCH_SB_CLEAN(c->disk_sb.sb, false);
 		c->sb.clean = false;
 		mutex_unlock(&c->sb_lock);
-		return NULL;
+		return ERR_PTR(-BCH_ERR_invalid_sb_clean);
 	}
 
 	clean = kmemdup(sb_clean, vstruct_bytes(&sb_clean->field),
-- 
2.43.0

Re: [PATCH] bcachefs: return err ptr instead of null in read sb clean

[Kent Overstreet]

On Tue, Sep 10, 2024 at 06:18:34PM GMT, Diogo Jahchan Koike wrote:
> syzbot reported a null-ptr-deref in bch2_fs_start. [0]
> 
> When a sb is marked clear but doesn't have a clean section
> bch2_read_superblock_clean returns NULL which PTR_ERR_OR_ZERO
> lets through, eventually leading to a null ptr dereference down
> the line. Adjust read sb clean to return an ERR_PTR indicating the
> invalid clean section.
> 
> [0] https://syzkaller.appspot.com/bug?extid=1cecc37d87c4286e5543
> 
> Reported-by: syzbot+1cecc37d87c4286e5543@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=1cecc37d87c4286e5543
> Signed-off-by: Diogo Jahchan Koike <djahchankoike@gmail.com>

Thanks, applied