Re: [PATCH] apparmor: check address length before reading AF_UNSPEC bind address

[John Johansen <john.johansen@canonical.com>]

On 10/20/26 07:00, Michail Andreas Michalopoulos wrote:
> bind_map_addr() handles AF_UNSPEC on an IPv4 socket by reading
> addr4->sin_addr.s_addr to check for INADDR_ANY. At that point the only
> length check done is addrlen >= offsetofend(struct sockaddr, sa_family),
> i.e. 2 bytes, while sin_addr sits at offset 4. move_addr_to_kernel()
> copies only addrlen bytes into the on-stack sockaddr_storage, so a
> bind() with a short AF_UNSPEC address makes AppArmor branch on bytes the
> caller never supplied.
> 
> Depending on those bytes, a confined task gets -EAFNOSUPPORT instead of
> the -EINVAL that inet_bind_sk() returns for the same request. Kernels
> built with CONFIG_INIT_STACK_ALL_ZERO read zeroes and happen to behave
> correctly.
> 
> Check the length first, as inet_bind_sk() does, and as the AF_INET6
> case above already does for inet6_bind_sk().
> 
> Fixes: 89ac6aa752ec ("apparmor: push inet mediation into profile callbacks, and improve auditing")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Michail Andreas Michalopoulos <mike.michalo@gmail.com>

sorry for the lateness of the reply,

Acked-by: John Johansen <john.johansen@canonical.com>

> ---
> Tested on v7.3 built with CONFIG_INIT_STACK_NONE in QEMU, with a task
> confined by a profile allowing all network access, calling bind() on an
> AF_INET UDP socket with {.sa_family = AF_UNSPEC} and addrlen 2 and 4
> (200 times each, after leaving a non-zero address in the kernel buffer):
> unpatched returns -EAFNOSUPPORT every time, patched returns -EINVAL
> every time, matching unconfined tasks. Other AF_UNSPEC, AF_INET and
> AF_INET6 bind cases behave identically with and without the patch.
> ---
>   security/apparmor/af_inet.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/security/apparmor/af_inet.c b/security/apparmor/af_inet.c
> index 516c9016537c..a617f8058634 100644
> --- a/security/apparmor/af_inet.c
> +++ b/security/apparmor/af_inet.c
> @@ -196,6 +196,9 @@ static int bind_map_addr(const struct sock *sk, struct sockaddr *addr,
>   		 * AF_UNSPEC if the address is INADDR_ANY
>   		 */
>   		addr4 = (struct sockaddr_in *)addr;
> +		/* Length check from inet_bind_sk() */
> +		if (addrlen < sizeof(struct sockaddr_in))
> +			return -EINVAL;
>   		if (addr4->sin_addr.s_addr != htonl(INADDR_ANY))
>   			return -EAFNOSUPPORT;
>   		family = AF_INET;