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Date: Wed, 24 Apr 2024 18:41:48 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Jeongjun Park <aha310510@gmail.com>
Cc: shaggy@kernel.org,
	syzbot+241c815bda521982cb49@syzkaller.appspotmail.com,
	brauner@kernel.org, jlayton@kernel.org, eadavis@qq.com,
	jfs-discussion@lists.sourceforge.net, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: [PATCH] jfs: Fix array-index-out-of-bounds in diFree
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 <20240424172240.148883-1-aha310510@gmail.com>
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On Thu, Apr 25, 2024 at 02:22:40AM +0900, Jeongjun Park wrote:
> Due to overflow, a value that is too large is entered into the agno 
> value. Therefore, we need to add code to check the agno value.

This is clearly wrong.

#define BLKTOAG(b,sbi)  ((b) >> ((sbi)->bmap->db_agl2size))

I'd suggest that something has either corrupted the sbi->bmap
pointer or the sbi->bmap->db_agl2size value.

All your patch does is cover up the problem, not fix it.

> Reported-by: syzbot+241c815bda521982cb49@syzkaller.appspotmail.com
> Signed-off-by: Jeongjun Park <aha310510@gmail.com>
> ---
>  fs/jfs/jfs_imap.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/fs/jfs/jfs_imap.c b/fs/jfs/jfs_imap.c
> index 2ec35889ad24..0aac083bc0db 100644
> --- a/fs/jfs/jfs_imap.c
> +++ b/fs/jfs/jfs_imap.c
> @@ -881,6 +881,11 @@ int diFree(struct inode *ip)
>  	 */
>  	agno = BLKTOAG(JFS_IP(ip)->agstart, JFS_SBI(ip->i_sb));
>  
> +	if(agno >= MAXAG || agno < 0){
> +		jfs_error(ip->i_sb, "invalid array index (0 <= agno < MAXAG), agno = %d\n", agno);
> +		return -ENOMEM;
> +	}
> +
>  	/* Lock the AG specific inode map information
>  	 */
>  	AG_LOCK(imap, agno);
> -- 
> 2.34.1
>