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

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Date: Wed, 26 Jun 2024 12:30:07 -0500
From: Dave Kleikamp <dave.kleikamp@...cle.com>
To: Edward Adam Davis <eadavis@...com>
Cc: 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: Re: [PATCH V2] jfs: fix null ptr deref in dtInsertEntry

Finally catching up on some neglected patches.

Looks good to me. Applied.

Shaggy

On 4/11/24 7:05AM, Edward Adam Davis wrote:
> [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