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@xxxxxxxxxx]
> Sent: Tuesday, December 1, 2020 11:15 PM
> To: Martin Schiller <ms@xxxxxxxxxx>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>;
> linux-x25@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; Andrew Hendry
> <andrew.hendry@xxxxxxxxx>; kiyin(尹亮) <kiyin@xxxxxxxxxxx>;
> security@xxxxxxxxxx; linux-distros@xxxxxxxxxxxxxxx; huntchen(陈阳)
> <huntchen@xxxxxxxxxxx>; dannywang(王宇) <dannywang@xxxxxxxxxxx>;
> kernel-janitors@xxxxxxxxxxxxxxx
> 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@xxxxxxxxxxx>
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> ---
> 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
