linux-kernel - Re: [PATCH V4] squashfs: Add i_size check in squash_read

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Message-ID: <20240802093310.twbwdi5hpgpth63z@quack3>
Date: Fri, 2 Aug 2024 11:33:10 +0200
From: Jan Kara <jack@...e.cz>
To: Lizhi Xu <lizhi.xu@...driver.com>
Cc: brauner@...nel.org, jack@...e.cz, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, phillip@...ashfs.org.uk,
	squashfs-devel@...ts.sourceforge.net,
	syzbot+24ac24ff58dc5b0d26b9@...kaller.appspotmail.com,
	syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: [PATCH V4] squashfs: Add i_size check in squash_read_inode

On Fri 02-08-24 11:01:14, Lizhi Xu wrote:
> syzbot report KMSAN: uninit-value in pick_link, the root cause is that
> squashfs_symlink_read_folio did not check the length, resulting in folio
> not being initialized and did not return the corresponding error code.
> 
> The length is calculated from i_size, so it is necessary to add a check
> when i_size is initialized to confirm that its value is correct, otherwise
> an error -EINVAL will be returned. Strictly, the check only applies to the
> symlink type.
> 
> Reported-and-tested-by: syzbot+24ac24ff58dc5b0d26b9@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=24ac24ff58dc5b0d26b9
> Signed-off-by: Lizhi Xu <lizhi.xu@...driver.com>
> ---
>  fs/squashfs/inode.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/fs/squashfs/inode.c b/fs/squashfs/inode.c
> index 16bd693d0b3a..6c5dd225482f 100644
> --- a/fs/squashfs/inode.c
> +++ b/fs/squashfs/inode.c
> @@ -287,6 +287,11 @@ int squashfs_read_inode(struct inode *inode, long long ino)
>  		inode->i_mode |= S_IFLNK;
>  		squashfs_i(inode)->start = block;
>  		squashfs_i(inode)->offset = offset;
> +		if ((int)inode->i_size < 0) {

Looks good. I think you could actually add even more agressive check like:

		if (inode->i_size > PAGE_SIZE) {

because larger symlink isn't supported by squashfs code anyway.

									Honza

> +			ERROR("Wrong i_size %d!\n", inode->i_size);
> +			return -EINVAL;
> +		}
> +
>  
>  		if (type == SQUASHFS_LSYMLINK_TYPE) {
>  			__le32 xattr;
> -- 
> 2.43.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR