Re: [PATCH] net: sctp, forbid negative length

[David Miller]

From: Jiri Slaby 
Date: Fri, 21 Oct 2016 14:13:24 +0200

> Most of getsockopt handlers in net/sctp/socket.c check len against
> sizeof some structure like:
> if (len < sizeof(int))
> return -EINVAL;
> 
> On the first look, the check seems to be correct. But since len is int
> and sizeof returns size_t, int gets promoted to unsigned size_t too. So
> the test returns false for negative lengths. Yes, (-1 < sizeof(long)) is
> false.
> 
> Fix this in sctp by explicitly checking len < 0 before any getsockopt
> handler is called.
> 
> Note that sctp_getsockopt_events already handled the negative case.
> Since we added the < 0 check elsewhere, this one can be removed.
> 
> If not checked, this is the result:
...
> Signed-off-by: Jiri Slaby 

Applied and queued up for -stable, thanks.

Re: [PATCH] net: sctp, forbid negative length

[Neil Horman]

On Fri, Oct 21, 2016 at 02:13:24PM +0200, Jiri Slaby wrote:
> Most of getsockopt handlers in net/sctp/socket.c check len against
> sizeof some structure like:
> if (len < sizeof(int))
> return -EINVAL;
> 
> On the first look, the check seems to be correct. But since len is int
> and sizeof returns size_t, int gets promoted to unsigned size_t too. So
> the test returns false for negative lengths. Yes, (-1 < sizeof(long)) is
> false.
> 
> Fix this in sctp by explicitly checking len < 0 before any getsockopt
> handler is called.
> 
> Note that sctp_getsockopt_events already handled the negative case.
> Since we added the < 0 check elsewhere, this one can be removed.
> 
> If not checked, this is the result:
> UBSAN: Undefined behaviour in ../mm/page_alloc.c:2722:19
> shift exponent 52 is too large for 32-bit type 'int'
> CPU: 1 PID: 24535 Comm: syz-executor Not tainted 4.8.1-0-syzkaller #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
> rel-1.9.1-0-gb3ef39f-prebuilt.qemu-project.org 04/01/2014
>   88006d99f2a8 b2f7bdea 41b58ab3
>  b4363c14 b2f7bcde 88006d99f2d0 88006d99f270
>    0034 b5096422
> Call Trace:
>  [] ? __ubsan_handle_shift_out_of_bounds+0x29c/0x300
> ...
>  [] ? kmalloc_order+0x24/0x90
>  [] ? kmalloc_order_trace+0x24/0x220
>  [] ? __kmalloc+0x330/0x540
>  [] ? sctp_getsockopt_local_addrs+0x174/0xca0 [sctp]
>  [] ? sctp_getsockopt+0x10d/0x1b0 [sctp]
>  [] ? sock_common_getsockopt+0xb9/0x150
>  [] ? SyS_getsockopt+0x1a5/0x270
> 
> Signed-off-by: Jiri Slaby 
> Cc: Vlad Yasevich 
> Cc: Neil Horman 
> Cc: "David S. Miller" 
> Cc: linux-s...@vger.kernel.org
> Cc: netdev@vger.kernel.org
> ---
>  net/sctp/socket.c | 5 -
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index fb02c7033307..9fbb6feb8c27 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -4687,7 +4687,7 @@ static int sctp_getsockopt_disable_fragments(struct 
> sock *sk, int len,
>  static int sctp_getsockopt_events(struct sock *sk, int len, char __user 
> *optval,
> int __user *optlen)
>  {
> - if (len <= 0)
> + if (len == 0)
>   return -EINVAL;
>   if (len > sizeof(struct sctp_event_subscribe))
>   len = sizeof(struct sctp_event_subscribe);
> @@ -6430,6 +6430,9 @@ static int sctp_getsockopt(struct sock *sk, int level, 
> int optname,
>   if (get_user(len, optlen))
>   return -EFAULT;
>  
> + if (len < 0)
> + return -EINVAL;
> +
>   lock_sock(sk);
>  
>   switch (optname) {
> -- 
> 2.10.1
> 
> 
Acked-by: Neil Horman 

[PATCH] net: sctp, forbid negative length

[Jiri Slaby]

Most of getsockopt handlers in net/sctp/socket.c check len against
sizeof some structure like:
if (len < sizeof(int))
return -EINVAL;

On the first look, the check seems to be correct. But since len is int
and sizeof returns size_t, int gets promoted to unsigned size_t too. So
the test returns false for negative lengths. Yes, (-1 < sizeof(long)) is
false.

Fix this in sctp by explicitly checking len < 0 before any getsockopt
handler is called.

Note that sctp_getsockopt_events already handled the negative case.
Since we added the < 0 check elsewhere, this one can be removed.

If not checked, this is the result:
UBSAN: Undefined behaviour in ../mm/page_alloc.c:2722:19
shift exponent 52 is too large for 32-bit type 'int'
CPU: 1 PID: 24535 Comm: syz-executor Not tainted 4.8.1-0-syzkaller #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
rel-1.9.1-0-gb3ef39f-prebuilt.qemu-project.org 04/01/2014
  88006d99f2a8 b2f7bdea 41b58ab3
 b4363c14 b2f7bcde 88006d99f2d0 88006d99f270
   0034 b5096422
Call Trace:
 [] ? __ubsan_handle_shift_out_of_bounds+0x29c/0x300
...
 [] ? kmalloc_order+0x24/0x90
 [] ? kmalloc_order_trace+0x24/0x220
 [] ? __kmalloc+0x330/0x540
 [] ? sctp_getsockopt_local_addrs+0x174/0xca0 [sctp]
 [] ? sctp_getsockopt+0x10d/0x1b0 [sctp]
 [] ? sock_common_getsockopt+0xb9/0x150
 [] ? SyS_getsockopt+0x1a5/0x270

Signed-off-by: Jiri Slaby 
Cc: Vlad Yasevich 
Cc: Neil Horman 
Cc: "David S. Miller" 
Cc: linux-s...@vger.kernel.org
Cc: netdev@vger.kernel.org
---
 net/sctp/socket.c | 5 -
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index fb02c7033307..9fbb6feb8c27 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -4687,7 +4687,7 @@ static int sctp_getsockopt_disable_fragments(struct sock 
*sk, int len,
 static int sctp_getsockopt_events(struct sock *sk, int len, char __user 
*optval,
  int __user *optlen)
 {
-   if (len <= 0)
+   if (len == 0)
return -EINVAL;
if (len > sizeof(struct sctp_event_subscribe))
len = sizeof(struct sctp_event_subscribe);
@@ -6430,6 +6430,9 @@ static int sctp_getsockopt(struct sock *sk, int level, 
int optname,
if (get_user(len, optlen))
return -EFAULT;
 
+   if (len < 0)
+   return -EINVAL;
+
lock_sock(sk);
 
switch (optname) {
-- 
2.10.1