| Message ID | 20201130100425.GB2789@kadam |
|---|---|
| State | New |
| Headers | show |
| Series | [net] net/x25: prevent a couple of overflows | expand |
On 2020-11-30 11:04, Dan Carpenter wrote: > From: "kiyin(尹亮)" <kiyin@tencent.com> > > 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. > > The x25 protocol only allows 15 character addresses so putting a NUL > terminator as the 16th character is safe and obviously preferable to > reading out of bounds. > OK, I see the potential danger. I'm just wondering what is the better approach here to counteract it: 1. check if the string is terminated or exceeds the maximum allowed length and report an error if necessary. 2. always terminate the string at byte 15 as you suggested. > Signed-off-by: "kiyin(尹亮)" <kiyin@tencent.com> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> > --- > > net/x25/af_x25.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c > index 0bbb283f23c9..3180f15942fe 100644 > --- a/net/x25/af_x25.c > +++ b/net/x25/af_x25.c > @@ -686,6 +686,8 @@ static int x25_bind(struct socket *sock, struct > sockaddr *uaddr, int addr_len) > goto out; > } > > + addr->sx25_addr.x25_addr[X25_ADDR_LEN - 1] = '\0'; > + > /* check for the null_x25_address */ > if (strcmp(addr->sx25_addr.x25_addr, null_x25_address.x25_addr)) { > > @@ -779,6 +781,7 @@ static int x25_connect(struct socket *sock, struct > sockaddr *uaddr, > goto out; > > rc = -ENETUNREACH; > + addr->sx25_addr.x25_addr[X25_ADDR_LEN - 1] = '\0'; > rt = x25_get_route(&addr->sx25_addr); > if (!rt) > goto out;
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
diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c index 0bbb283f23c9..3180f15942fe 100644 --- a/net/x25/af_x25.c +++ b/net/x25/af_x25.c @@ -686,6 +686,8 @@ static int x25_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len) goto out; } + addr->sx25_addr.x25_addr[X25_ADDR_LEN - 1] = '\0'; + /* check for the null_x25_address */ if (strcmp(addr->sx25_addr.x25_addr, null_x25_address.x25_addr)) { @@ -779,6 +781,7 @@ static int x25_connect(struct socket *sock, struct sockaddr *uaddr, goto out; rc = -ENETUNREACH; + addr->sx25_addr.x25_addr[X25_ADDR_LEN - 1] = '\0'; rt = x25_get_route(&addr->sx25_addr); if (!rt) goto out;