Re: [PATCH 2/5] CVE-2025-26724: fs: cramfs: fix malloc(size + constant) buffer overflow issues

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 19.02.25 15:18, Sascha Hauer wrote:
> The pattern malloc(size + constant) is dangerous when size can be
> manipulated by an attacker. In that case 'size' can be manipulated
> in a way that 'size + constant' is 0 due to integer overflow. The
> result is a zero sized buffer to which is then data written to.
> 
> Avoid this by using size_add() instead.

For those unfamiliar with size_add(), it does a saturation addition
and thus xzalloc() will fail as it's impossible to allocate
SIZE_MAX bytes.

> 
> Reported-by: Jonathan Bar Or <jonathanbaror@gmail.com>
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

Thanks,
Ahmad

> ---
>  fs/cramfs/cramfs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/cramfs/cramfs.c b/fs/cramfs/cramfs.c
> index e554ebef6f..641a6d2b05 100644
> --- a/fs/cramfs/cramfs.c
> +++ b/fs/cramfs/cramfs.c
> @@ -423,7 +423,7 @@ static const char *cramfs_get_link(struct dentry *dentry, struct inode *inode)
>  {
>  	int ret;
>  
> -	inode->i_link = xzalloc(inode->i_size + 1);
> +	inode->i_link = xzalloc(size_add(inode->i_size, 1));
>  
>  	ret = cramfs_read_file(inode, 0, inode->i_link, inode->i_size);
>  	if (ret < 0)


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