linux-kernel - [PATCH v4] fs/sysv: Null check to prevent null-ptr-deref bug

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Date:   Tue, 30 May 2023 18:31:41 -0700
From:   Prince Kumar Maurya <princekumarmaurya06@...il.com>
To:     skhan@...uxfoundation.org, brauner@...nel.org, dchinner@...hat.com,
        viro@...iv.linux.org.uk, chenzhongjin@...wei.com
Cc:     Prince Kumar Maurya <princekumarmaurya06@...il.com>,
        linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzkaller-bugs@...glegroups.com, linux-fsdevel@...r.kernel.org,
        syzbot+aad58150cbc64ba41bdc@...kaller.appspotmail.com
Subject: [PATCH v4] fs/sysv: Null check to prevent null-ptr-deref bug

sb_getblk(inode->i_sb, parent) return a null ptr and taking lock on
that leads to the null-ptr-deref bug.

Reported-by: syzbot+aad58150cbc64ba41bdc@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=aad58150cbc64ba41bdc 
Signed-off-by: Prince Kumar Maurya <princekumarmaurya06@...il.com>
---
Change since v3: Added cleanup code for the branch[n].key on 
failure code path.

 fs/sysv/itree.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/sysv/itree.c b/fs/sysv/itree.c
index b22764fe669c..58d7f43a1371 100644
--- a/fs/sysv/itree.c
+++ b/fs/sysv/itree.c
@@ -145,6 +145,10 @@ static int alloc_branch(struct inode *inode,
 		 */
 		parent = block_to_cpu(SYSV_SB(inode->i_sb), branch[n-1].key);
 		bh = sb_getblk(inode->i_sb, parent);
+		if (!bh) {
+			sysv_free_block(inode->i_sb, branch[n].key);
+			break;
+		}
 		lock_buffer(bh);
 		memset(bh->b_data, 0, blocksize);
 		branch[n].bh = bh;
-- 
2.40.1