linux-kernel - [PATCH AUTOSEL 6.4 05/16] fs/sysv: Null check to prevent null-ptr-deref bug

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Date:   Sun,  2 Jul 2023 15:38:04 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Prince Kumar Maurya <princekumarmaurya06@...il.com>,
        syzbot+aad58150cbc64ba41bdc@...kaller.appspotmail.com,
        Christian Brauner <brauner@...nel.org>,
        Sasha Levin <sashal@...nel.org>, viro@...iv.linux.org.uk,
        chenzhongjin@...wei.com, dchinner@...hat.com
Subject: [PATCH AUTOSEL 6.4 05/16] fs/sysv: Null check to prevent null-ptr-deref bug

From: Prince Kumar Maurya <princekumarmaurya06@...il.com>

[ Upstream commit ea2b62f305893992156a798f665847e0663c9f41 ]

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>
Message-Id: <20230531013141.19487-1-princekumarmaurya06@...il.com>
Signed-off-by: Christian Brauner <brauner@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/sysv/itree.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/sysv/itree.c b/fs/sysv/itree.c
index b22764fe669c8..58d7f43a13712 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;
-- 
2.39.2