Re: [PATCH] RDMA/cma: Distinguish between sockaddr_in and sockaddr_in6 by size

[Nathan Chancellor]

On Wed, Feb 08, 2023 at 03:25:53PM -0800, Kees Cook wrote:
> Clang can do some aggressive inlining, which provides it with greater
> visibility into the sizes of various objects that are passed into
> helpers. Specifically, compare_netdev_and_ip() can see through the type
> given to the "sa" argument, which means it can generate code for "struct
> sockaddr_in" that would have been passed to ipv6_addr_cmp() (that expects
> to operate on the larger "struct sockaddr_in6"), which would result in a
> compile-time buffer overflow condition detected by memcmp(). Logically,
> this state isn't reachable due to the sa_family assignment two callers
> above and the check in compare_netdev_and_ip(). Instead, provide a
> compile-time check on sizes so the size-mismatched code will be elided
> when inlining. Avoids the following warning from Clang:
> 
> ../include/linux/fortify-string.h:652:4: error: call to '__read_overflow' declared with 'error' attribute: detected read beyond size of object (1st parameter)
>                         __read_overflow();
>                         ^
> note: In function 'cma_netevent_callback'
> note:   which inlined function 'node_from_ndev_ip'
> 1 error generated.
> 
> When the underlying object size is not known (e.g. with GCC and older
> Clang), the result of __builtin_object_size() is SIZE_MAX, which
> will also compile away, leaving the code as it was originally.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1687
> Cc: Jason Gunthorpe <jgg@xxxxxxxx>
> Cc: Leon Romanovsky <leon@xxxxxxxxxx>
> Cc: Mark Zhang <markzhang@xxxxxxxxxx>
> Cc: Patrisious Haddad <phaddad@xxxxxxxxxx>
> Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
> Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Cc: linux-rdma@xxxxxxxxxxxxxxx
> Cc: llvm@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx> # build

Should this have a 'Cc: stable@xxxxxxxxxxxxxxx', since we see this in
6.1?

> ---
>  drivers/infiniband/core/cma.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
> index 1d2bff91d78b..308155937713 100644
> --- a/drivers/infiniband/core/cma.c
> +++ b/drivers/infiniband/core/cma.c
> @@ -479,13 +479,20 @@ static int compare_netdev_and_ip(int ifindex_a, struct sockaddr *sa,
>  	if (sa->sa_family != sb->sa_family)
>  		return sa->sa_family - sb->sa_family;
>  
> -	if (sa->sa_family == AF_INET)
> -		return memcmp((char *)&((struct sockaddr_in *)sa)->sin_addr,
> -			      (char *)&((struct sockaddr_in *)sb)->sin_addr,
> +	if (sa->sa_family == AF_INET &&
> +	    __builtin_object_size(sa, 0) >= sizeof(struct sockaddr_in)) {
> +		return memcmp(&((struct sockaddr_in *)sa)->sin_addr,
> +			      &((struct sockaddr_in *)sb)->sin_addr,
>  			      sizeof(((struct sockaddr_in *)sa)->sin_addr));
> +	}
> +
> +	if (sa->sa_family == AF_INET6 &&
> +	    __builtin_object_size(sa, 0) >= sizeof(struct sockaddr_in6)) {
> +		return ipv6_addr_cmp(&((struct sockaddr_in6 *)sa)->sin6_addr,
> +				     &((struct sockaddr_in6 *)sb)->sin6_addr);
> +	}
>  
> -	return ipv6_addr_cmp(&((struct sockaddr_in6 *)sa)->sin6_addr,
> -			     &((struct sockaddr_in6 *)sb)->sin6_addr);
> +	return -1;
>  }
>  
>  static int cma_add_id_to_tree(struct rdma_id_private *node_id_priv)
> -- 
> 2.34.1
>