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

[Sasha Levin]

From: Prince Kumar Maurya <princekumarmaurya06@xxxxxxxxx>

[ 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@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=aad58150cbc64ba41bdc
Signed-off-by: Prince Kumar Maurya <princekumarmaurya06@xxxxxxxxx>
Message-Id: <20230531013141.19487-1-princekumarmaurya06@xxxxxxxxx>
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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