linux-kernel - [PATCH v2] erofs: fix null-ptr-deref caused by erofs_xattr_prefixes

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Message-Id: <20230515103941.129784-1-jefflexu@linux.alibaba.com>
Date:   Mon, 15 May 2023 18:39:41 +0800
From:   Jingbo Xu <jefflexu@...ux.alibaba.com>
To:     xiang@...nel.org, chao@...nel.org, huyue2@...lpad.com,
        linux-erofs@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH v2] 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@...kaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=902d5a9373ae8f748a94
Fixes: 9e382914617c ("erofs: add helpers to load long xattr name prefixes")
Signed-off-by: Jingbo Xu <jefflexu@...ux.alibaba.com>
---
v2: polish the commit message (Gao Xiang)
---
 fs/erofs/xattr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/erofs/xattr.c b/fs/erofs/xattr.c
index cd80499351e0..bbfe7ce170d2 100644
--- 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);
-- 
2.19.1.6.gb485710b