[PATCH 5.15.y] jfs: fix null ptr deref in dtInsertEntry

[Aditya Dutt]

From: Edward Adam Davis <eadavis@xxxxxx>

[ Upstream commit ce6dede912f064a855acf6f04a04cbb2c25b8c8c ]

[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.

Closes: https://syzkaller.appspot.com/bug?extid=30b3e48dc48dd2ad45b6
Reported-by: syzbot+30b3e48dc48dd2ad45b6@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+bba84aef3a26fb93deb9@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
Signed-off-by: Dave Kleikamp <dave.kleikamp@xxxxxxxxxx>
Signed-off-by: Aditya Dutt <duttaditya18@xxxxxxxxx>
---

I tested the patch manually using the C reproducer:
https://syzkaller.appspot.com/text?tag=ReproC&x=135c9b70580000
given in the syzkaller dashboard above.

 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 27ca98614b0b..cb57d4f1161f 100644
--- a/fs/jfs/jfs_dtree.c
+++ b/fs/jfs/jfs_dtree.c
@@ -835,6 +835,8 @@ 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
-- 
2.34.1