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Date:   Wed, 02 Dec 2020 10:27:18 +0100
From:   Martin Schiller <ms@....tdt.de>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-x25@...r.kernel.org,
        netdev@...r.kernel.org, Andrew Hendry <andrew.hendry@...il.com>,
        kiyin(尹亮) 
        <kiyin@...cent.com>, security@...nel.org,
        linux-distros@...openwall.org,
        huntchen(陈阳) 
        <huntchen@...cent.com>,
        dannywang(王宇) 
        <dannywang@...cent.com>, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net v2] net/x25: prevent a couple of overflows

On 2020-12-01 16:15, Dan Carpenter wrote:
> 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@...cent.com>
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.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;

Acked-by: Martin Schiller <ms@....tdt.de>

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