Patchwork netlink: fix (theoretical) overrun in message iteration

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Submitter Vegard Nossum
Date Dec. 21, 2008, 1:42 p.m.
Message ID <20081221134218.GA7959@localhost.localdomain>
Download mbox | patch
Permalink /patch/15133/
State Accepted
Delegated to: David Miller
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Comments

Vegard Nossum - Dec. 21, 2008, 1:42 p.m.
From bb805d89e84ddb11c9bb58afcfd9a6b37bbe5a9b Mon Sep 17 00:00:00 2001
From: Vegard Nossum <vegard.nossum@gmail.com>
Date: Sun, 21 Dec 2008 14:20:49 +0100
Subject: [PATCH] netlink: fix (theoretical) overrun in message iteration

See commit 1045b03e07d85f3545118510a587035536030c1c for a detailed
explanation of why this patch is necessary.

In short, nlmsg_next() can make "remaining" go negative, and the
remaining >= sizeof(...) comparison will promote "remaining" to an
unsigned type, which means that the expression will evaluate to
true for negative numbers, even though it was not intended.

I put "theoretical" in the title because I have no evidence that
this can actually happen, but I suspect that a crafted netlink
packet can trigger some badness.

Note that the last test, which seemingly has the exact same
problem (also true for nla_ok()), is perfectly OK, since we
already know that remaining is positive.

Cc: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>
---
 include/net/netlink.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
Vegard Nossum - Dec. 21, 2008, 2:44 p.m.
On Sun, Dec 21, 2008 at 2:42 PM, Vegard Nossum <vegard.nossum@gmail.com> wrote:
> From bb805d89e84ddb11c9bb58afcfd9a6b37bbe5a9b Mon Sep 17 00:00:00 2001
> From: Vegard Nossum <vegard.nossum@gmail.com>
> Date: Sun, 21 Dec 2008 14:20:49 +0100
> Subject: [PATCH] netlink: fix (theoretical) overrun in message iteration
>
> See commit 1045b03e07d85f3545118510a587035536030c1c for a detailed
> explanation of why this patch is necessary.
>
> In short, nlmsg_next() can make "remaining" go negative, and the
> remaining >= sizeof(...) comparison will promote "remaining" to an
> unsigned type, which means that the expression will evaluate to
> true for negative numbers, even though it was not intended.
>
> I put "theoretical" in the title because I have no evidence that
> this can actually happen, but I suspect that a crafted netlink
> packet can trigger some badness.

nlmsg
Vegard Nossum - Dec. 21, 2008, 2:46 p.m.
On Sun, Dec 21, 2008 at 3:44 PM, Vegard Nossum <vegard.nossum@gmail.com> wrote:
> On Sun, Dec 21, 2008 at 2:42 PM, Vegard Nossum <vegard.nossum@gmail.com> wrote:
>> From bb805d89e84ddb11c9bb58afcfd9a6b37bbe5a9b Mon Sep 17 00:00:00 2001
>> From: Vegard Nossum <vegard.nossum@gmail.com>
>> Date: Sun, 21 Dec 2008 14:20:49 +0100
>> Subject: [PATCH] netlink: fix (theoretical) overrun in message iteration
>>
>> See commit 1045b03e07d85f3545118510a587035536030c1c for a detailed
>> explanation of why this patch is necessary.
>>
>> In short, nlmsg_next() can make "remaining" go negative, and the
>> remaining >= sizeof(...) comparison will promote "remaining" to an
>> unsigned type, which means that the expression will evaluate to
>> true for negative numbers, even though it was not intended.
>>
>> I put "theoretical" in the title because I have no evidence that
>> this can actually happen, but I suspect that a crafted netlink
>> packet can trigger some badness.
>
> nlmsg

Oops. I meant to say that nlmsg_for_each_msg() has no users at all,
which means that the change is all the more "theoretical" :-)


Vegard
David Miller - Dec. 26, 2008, 1:20 a.m.
From: Vegard Nossum <vegard.nossum@gmail.com>
Date: Sun, 21 Dec 2008 14:42:18 +0100

> netlink: fix (theoretical) overrun in message iteration

I'll apply this but we should also consider getting rid
of unused interfaces such as nlmsg_for_each_msg().

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Patch

diff --git a/include/net/netlink.h b/include/net/netlink.h
index 3643bbb..13dd525 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -332,7 +332,7 @@  static inline int nlmsg_attrlen(const struct nlmsghdr *nlh, int hdrlen)
  */
 static inline int nlmsg_ok(const struct nlmsghdr *nlh, int remaining)
 {
-	return (remaining >= sizeof(struct nlmsghdr) &&
+	return (remaining >= (int) sizeof(struct nlmsghdr) &&
 		nlh->nlmsg_len >= sizeof(struct nlmsghdr) &&
 		nlh->nlmsg_len <= remaining);
 }