ext4: no need to continue when the number of entries is 1

JIRA: https://issues.redhat.com/browse/RHEL-64524
CVE: CVE-2024-49967

commit 1a00a39
Author: Edward Adam Davis <eadavis@qq.com>
Date:   Mon Jul 1 22:25:03 2024 +0800

    ext4: no need to continue when the number of entries is 1

    Fixes: ac27a0e ("[PATCH] ext4: initial copy of files from ext3")
    Reported-by: syzbot+ae688d469e36fb5138d0@syzkaller.appspotmail.com
    Closes: https://syzkaller.appspot.com/bug?extid=ae688d469e36fb5138d0
    Signed-off-by: Edward Adam Davis <eadavis@qq.com>
    Reported-and-tested-by: syzbot+ae688d469e36fb5138d0@syzkaller.appspotmail.com
    Link: https://patch.msgid.link/tencent_BE7AEE6C7C2D216CB8949CE8E6EE7ECC2C0A@qq.com
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Cc: stable@kernel.org

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

fs/ext4/namei.c

@@ -2046,7 +2046,7 @@ static struct ext4_dir_entry_2 *do_split(handle_t *handle, struct inode *dir,
 		split = count/2;
 
 	hash2 = map[split].hash;
-	continued = hash2 == map[split - 1].hash;
+	continued = split > 0 ? hash2 == map[split - 1].hash : 0;
 	dxtrace(printk(KERN_INFO "Split block %lu at %x, %i/%i\n",
 			(unsigned long)dx_get_block(frame->at),
 					hash2, split, count-split));