linux-kernel - [PATCH V2] jfs: fix null ptr deref in dtInsertEntry

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Date: Thu, 11 Apr 2024 20:05:28 +0800
From: Edward Adam Davis <eadavis@...com>
To: dave.kleikamp@...cle.com
Cc: eadavis@...com,
	jfs-discussion@...ts.sourceforge.net,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	syzbot+bba84aef3a26fb93deb9@...kaller.appspotmail.com,
	syzkaller-bugs@...glegroups.com
Subject: [PATCH V2] jfs: fix null ptr deref in dtInsertEntry

[syzbot reported]
general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 0 PID: 5061 Comm: syz-executor404 Not tainted 6.8.0-syzkaller-08951-gfe46a7dd189e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
RIP: 0010:dtInsertEntry+0xd0c/0x1780 fs/jfs/jfs_dtree.c:3713
..
[Analyze]
In dtInsertEntry(), when the pointer h has the same value as p, after writing
name in UniStrncpy_to_le(), p->header.flag will be cleared. This will cause the
previously true judgment "p->header.flag & BT-LEAF" to change to no after writing
the name operation, this leads to entering an incorrect branch and accessing the
uninitialized object ih when judging this condition for the second time.

[Fix]
After got the page, check freelist first, if freelist == 0 then exit dtInsert()
and return -EINVAL.

Reported-by: syzbot+bba84aef3a26fb93deb9@...kaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@...com>
---
 fs/jfs/jfs_dtree.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/jfs/jfs_dtree.c b/fs/jfs/jfs_dtree.c
index 031d8f570f58..5d3127ca68a4 100644
--- a/fs/jfs/jfs_dtree.c
+++ b/fs/jfs/jfs_dtree.c
@@ -834,6 +834,8 @@ int dtInsert(tid_t tid, struct inode *ip,
 	 * the full page.
 	 */
 	DT_GETSEARCH(ip, btstack->top, bn, mp, p, index);
+	if (p->header.freelist == 0)
+		return -EINVAL;

 	/*
 	 *	insert entry for new key
-- 
2.43.0