linux-kernel - [syzbot] [ext4?] BUG: unable to handle kernel paging request in do

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Date: Sun, 30 Jun 2024 17:09:42 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+ae688d469e36fb5138d0@...kaller.appspotmail.com
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: [syzbot] [ext4?] BUG: unable to handle kernel paging request in do_split

if split is too small, such as 0, use it to calculate continued will out of bound map

#syz test: upstream 55027e689933

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index a630b27a4cc6..0a111274dc4a 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -2043,7 +2043,7 @@ 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));