Re: [PATCH] ntfs3: harden against integer overflows

[Konstantin Komarov <almaz.alexandrovich@paragon-software.com>]

On 9/12/22 18:08, Dan Carpenter wrote:
> Smatch complains that the "add_bytes" is not to be trusted.  Use
> size_add() to prevent an integer overflow.
> 
> Fixes: be71b5cba2e6 ("fs/ntfs3: Add attrib operations")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> The add_bytes variable comes from:
> 
> 	add = ALIGN(struct_size(ea_all, name, 1 + name_len + val_size), 4);
> 
> This is problematic and has inspired a new static checker warning:
> 
> fs/ntfs3/xattr.c:26 unpacked_ea_size() warn: using integer overflow function 'size_add()' for math
> fs/ntfs3/xattr.c:290 ntfs_set_ea() warn: using integer overflow function 'size_add()' for math
> 
> The issue is that the struct_size() has an integer overflow and we call
> ALIGN() on it, then "add" becomes zero.  Is there a bounds check that
> we could use here?
> 
> 	add = struct_size(ea_all, name, 1 + name_len + val_size);
> 	if (add > SOMETHING_MAX)
> 		return -EINVAL;
> 
> Otherwise the limit would have to be if (add > ULONG_MAX - 3) { which
> is ugly.
> 
>   fs/ntfs3/xattr.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ntfs3/xattr.c b/fs/ntfs3/xattr.c
> index 7de8718c68a9..ea582b4fe1d9 100644
> --- a/fs/ntfs3/xattr.c
> +++ b/fs/ntfs3/xattr.c
> @@ -107,7 +107,7 @@ static int ntfs_read_ea(struct ntfs_inode *ni, struct EA_FULL **ea,
>   		return -EFBIG;
>   
>   	/* Allocate memory for packed Ea. */
> -	ea_p = kmalloc(size + add_bytes, GFP_NOFS);
> +	ea_p = kmalloc(size_add(size, add_bytes), GFP_NOFS);
>   	if (!ea_p)
>   		return -ENOMEM;
>   

Applied, thanks!