RE: [PATCH net v2] net/x25: prevent a couple of overflows(Internet mail)

["kiyin(尹亮)" <kiyin@tencent.com>]

Hi Dan,
    I think the strnlen is better. the kernel doesn't need to adjust user land mistake by putting a NULL terminator. just return an error to let the user land program fix the wrong address.

Regards,
kiyin

> -----Original Message-----
> From: Dan Carpenter [mailto:dan.carpenter@oracle.com]
> Sent: Tuesday, December 1, 2020 11:15 PM
> To: Martin Schiller <ms@dev.tdt.de>
> Cc: David S. Miller <davem@davemloft.net>; Jakub Kicinski <kuba@kernel.org>;
> linux-x25@vger.kernel.org; netdev@vger.kernel.org; Andrew Hendry
> <andrew.hendry@gmail.com>; kiyin(尹亮) <kiyin@tencent.com>;
> security@kernel.org; linux-distros@vs.openwall.org; huntchen(陈阳)
> <huntchen@tencent.com>; dannywang(王宇) <dannywang@tencent.com>;
> kernel-janitors@vger.kernel.org
> Subject: [PATCH net v2] net/x25: prevent a couple of overflows(Internet mail)
> 
> The .x25_addr[] address comes from the user and is not necessarily NUL
> terminated.  This leads to a couple problems.  The first problem is that the
> strlen() in x25_bind() can read beyond the end of the buffer.
> 
> The second problem is more subtle and could result in memory corruption.
> The call tree is:
>   x25_connect()
>   --> x25_write_internal()
>       --> x25_addr_aton()
> 
> The .x25_addr[] buffers are copied to the "addresses" buffer from
> x25_write_internal() so it will lead to stack corruption.
> 
> Verify that the strings are NUL terminated and return -EINVAL if they are not.
> 
> Reported-by: "kiyin(尹亮)" <kiyin@tencent.com>
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> The first patch put a NUL terminator on the end of the string and this patch
> returns an error instead.  I don't have a strong preference, which patch to go
> with.
> 
>  net/x25/af_x25.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c index
> 9232cdb42ad9..d41fffb2507b 100644
> --- a/net/x25/af_x25.c
> +++ b/net/x25/af_x25.c
> @@ -675,7 +675,8 @@ static int x25_bind(struct socket *sock, struct
> sockaddr *uaddr, int addr_len)
>  	int len, i, rc = 0;
> 
>  	if (addr_len != sizeof(struct sockaddr_x25) ||
> -	    addr->sx25_family != AF_X25) {
> +	    addr->sx25_family != AF_X25 ||
> +	    strnlen(addr->sx25_addr.x25_addr, X25_ADDR_LEN) ==
> X25_ADDR_LEN) {
>  		rc = -EINVAL;
>  		goto out;
>  	}
> @@ -769,7 +770,8 @@ static int x25_connect(struct socket *sock, struct
> sockaddr *uaddr,
> 
>  	rc = -EINVAL;
>  	if (addr_len != sizeof(struct sockaddr_x25) ||
> -	    addr->sx25_family != AF_X25)
> +	    addr->sx25_family != AF_X25 ||
> +	    strnlen(addr->sx25_addr.x25_addr, X25_ADDR_LEN) ==
> X25_ADDR_LEN)
>  		goto out;
> 
>  	rc = -ENETUNREACH;
> --
> 2.29.2