Re: [PATCH 03/11] security: commoncap: fix -Wstringop-overread warning

[Christian Brauner]

On Mon, Mar 22, 2021 at 05:02:41PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> gcc-11 introdces a harmless warning for cap_inode_getsecurity:
> 
> security/commoncap.c: In function ‘cap_inode_getsecurity’:
> security/commoncap.c:440:33: error: ‘memcpy’ reading 16 bytes from a region of size 0 [-Werror=stringop-overread]
>   440 |                                 memcpy(&nscap->data, &cap->data, sizeof(__le32) * 2 * VFS_CAP_U32);
>       |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> The problem here is that tmpbuf is initialized to NULL, so gcc assumes
> it is not accessible unless it gets set by vfs_getxattr_alloc().  This is
> a legitimate warning as far as I can tell, but the code is correct since
> it correctly handles the error when that function fails.
> 
> Add a separate NULL check to tell gcc about it as well.
> 
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---

Seems reasonable,
Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>