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[PATCH] sctp: use GFP_USER for user-controlled kmalloc

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  [PATCH] sctp: use GFP_USER for user-controlled kmalloc Marcelo Ricardo Leitner <marcelo.leitner@gmail.com> - 2015-11-30 17:40 +0100
    RE: [PATCH] sctp: use GFP_USER for user-controlled kmalloc David Laight <David.Laight@ACULAB.COM> - 2015-12-01 11:50 +0100
      Re: [PATCH] sctp: use GFP_USER for user-controlled kmalloc Daniel Borkmann <daniel@iogearbox.net> - 2015-12-01 12:30 +0100
    Re: [PATCH] sctp: use GFP_USER for user-controlled kmalloc David Miller <davem@davemloft.net> - 2015-12-03 05:50 +0100

#1280092 — [PATCH] sctp: use GFP_USER for user-controlled kmalloc

Dmitry Vyukov reported that the user could trigger a kernel warning by
using a large len value for getsockopt SCTP_GET_LOCAL_ADDRS, as that
value directly affects the value used as a kmalloc() parameter.

This patch thus switches the allocation flags from all user-controllable
kmalloc size to GFP_USER to put some more restrictions on it and also
disables the warn, as they are not necessary.

Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
---
 net/sctp/socket.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 897c01c029cab3d5805cc56b0964c70e06f4143a..676b3bb092e16848fd1c822e1c999af4a2ef198d 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -972,7 +972,7 @@ static int sctp_setsockopt_bindx(struct sock *sk,
 		return -EFAULT;
 
 	/* Alloc space for the address array in kernel memory.  */
-	kaddrs = kmalloc(addrs_size, GFP_KERNEL);
+	kaddrs = kmalloc(addrs_size, GFP_USER | __GFP_NOWARN);
 	if (unlikely(!kaddrs))
 		return -ENOMEM;
 
@@ -4928,7 +4928,7 @@ static int sctp_getsockopt_local_addrs(struct sock *sk, int len,
 	to = optval + offsetof(struct sctp_getaddrs, addrs);
 	space_left = len - offsetof(struct sctp_getaddrs, addrs);
 
-	addrs = kmalloc(space_left, GFP_KERNEL);
+	addrs = kmalloc(space_left, GFP_USER | __GFP_NOWARN);
 	if (!addrs)
 		return -ENOMEM;
 
-- 
2.5.0

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#1280748

From: Marcelo Ricardo Leitner
> Sent: 30 November 2015 16:33
> Dmitry Vyukov reported that the user could trigger a kernel warning by
> using a large len value for getsockopt SCTP_GET_LOCAL_ADDRS, as that
> value directly affects the value used as a kmalloc() parameter.
> 
> This patch thus switches the allocation flags from all user-controllable
> kmalloc size to GFP_USER to put some more restrictions on it and also
> disables the warn, as they are not necessary.

ISTM that the code should put some 'sanity limit' on that
size before allocating the kernel buffer.

	David

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#1280791

On 12/01/2015 11:46 AM, David Laight wrote:
> From: Marcelo Ricardo Leitner
>> Sent: 30 November 2015 16:33
>> Dmitry Vyukov reported that the user could trigger a kernel warning by
>> using a large len value for getsockopt SCTP_GET_LOCAL_ADDRS, as that
>> value directly affects the value used as a kmalloc() parameter.
>>
>> This patch thus switches the allocation flags from all user-controllable
>> kmalloc size to GFP_USER to put some more restrictions on it and also
>> disables the warn, as they are not necessary.
>
> ISTM that the code should put some 'sanity limit' on that
> size before allocating the kernel buffer.

One could do that in addition, but this buffer has just a short lifetime
and by using GFP_USER hardwall restrictions apply already.
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#1282705

From: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Date: Mon, 30 Nov 2015 14:32:54 -0200

> Dmitry Vyukov reported that the user could trigger a kernel warning by
> using a large len value for getsockopt SCTP_GET_LOCAL_ADDRS, as that
> value directly affects the value used as a kmalloc() parameter.
> 
> This patch thus switches the allocation flags from all user-controllable
> kmalloc size to GFP_USER to put some more restrictions on it and also
> disables the warn, as they are not necessary.
> 
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
> Acked-by: Daniel Borkmann <daniel@iogearbox.net>

Applied.
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