erofs: fix null-ptr-deref caused by erofs_xattr_prefixes_init

Fragments and dedupe share one feature bit, and thus packed inode may not
exist when fragment feature bit (dedupe feature bit exactly) is set, e.g.
when deduplication feature is in use while fragments feature is not.  In
this case, sbi->packed_inode could be NULL while fragments feature bit
is set.

Fix this by accessing packed inode only when it exists.

Reported-by: syzbot+902d5a9373ae8f748a94@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=902d5a9373ae8f748a94
Reported-and-tested-by: syzbot+bbb353775d51424087f2@syzkaller.appspotmail.com
Fixes: 9e382914617c ("erofs: add helpers to load long xattr name prefixes")
Fixes: 6a318ccd7e08 ("erofs: enable long extended attribute name prefixes")
Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230515103941.129784-1-jefflexu@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

diff --git a/fs/erofs/xattr.c b/fs/erofs/xattr.c
index cd80499351e05c1e3900a71f468b51eaa8d009ad..bbfe7ce170d217f30ec4a838c65df1b6c16fd463 100644 (file)
--- a/fs/erofs/xattr.c
+++ b/fs/erofs/xattr.c
@@ -675,7 +675,7 @@ int erofs_xattr_prefixes_init(struct super_block *sb)
        if (!pfs)
                return -ENOMEM;
 
-       if (erofs_sb_has_fragments(sbi))
+       if (sbi->packed_inode)
                buf.inode = sbi->packed_inode;
        else
                erofs_init_metabuf(&buf, sb);