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@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=aad58150cbc64ba41bdc
Signed-off-by: Prince Kumar Maurya <princekumarmaurya06@gmail.com>
Message-Id: <20230531013141.19487-1-princekumarmaurya06@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/sysv/itree.c b/fs/sysv/itree.c
index b22764f..58d7f43 100644 (file)
--- 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;