linux-kernel - Re: [PATCH] sctp: fix a potential missing-check bug

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Message-ID: <CAAa=b7eebr23Pjs2LE0Ri0=gki8ZDAbLmfPWOqzWHO0i6E2aNA@mail.gmail.com>
Date:   Thu, 3 May 2018 07:01:51 -0500
From:   Wenwen Wang <wang6495@....edu>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     Kangjie Lu <kjlu@....edu>, Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        "David S. Miller" <davem@...emloft.net>,
        "open list:SCTP PROTOCOL" <linux-sctp@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Wenwen Wang <wang6495@....edu>
Subject: Re: [PATCH] sctp: fix a potential missing-check bug

On Wed, May 2, 2018 at 8:48 PM, Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
> On Wed, May 02, 2018 at 08:27:05PM -0500, Wenwen Wang wrote:
>> On Wed, May 2, 2018 at 8:24 PM, Marcelo Ricardo Leitner
>> <marcelo.leitner@...il.com> wrote:
>> > On Wed, May 02, 2018 at 08:15:45PM -0500, Wenwen Wang wrote:
>> >> In sctp_setsockopt_maxseg(), the integer 'val' is compared against min_len
>> >> and max_len to check whether it is in the appropriate range. If it is not,
>> >> an error code -EINVAL will be returned. This is enforced by a security
>> >> check. But, this check is only executed when 'val' is not 0. In fact, if
>> >> 'val' is 0, it will be assigned with a new value (if the return value of
>> >> the function sctp_id2assoc() is not 0) in the following execution. However,
>> >> this new value of 'val' is not checked before it is used to assigned to
>> >> asoc->user_frag. That means it is possible that the new value of 'val'
>> >> could be out of the expected range. This can cause security issues
>> >> such as buffer overflows, e.g., the new value of 'val' is used as an index
>> >> to access a buffer.
>> >>
>> >> This patch inserts a check for the new value of 'val' to see if it is in
>> >> the expected range. If it is not, an error code -EINVAL will be returned.
>> >>
>> >> Signed-off-by: Wenwen Wang <wang6495@....edu>
>> >> ---
>> >>  net/sctp/socket.c | 22 +++++++++++-----------
>> >>  1 file changed, 11 insertions(+), 11 deletions(-)
>> >
>> > ?
>> > This patch is the same as previous one. git send-email <old file>
>> > maybe?
>> >
>> >   Marcelo
>>
>> Thanks for your suggestion, Marcelo. I can send the old file. But, I
>> have added a line of comment in this patch.
>
> I meant if you had sent the old patch again by accident, because you
> said you worked on an old version of the tree, but then posted a patch
> that also doesn't use the new MTU function I mentioned.
>
>   Marcelo

I worked on the latest kernel. But, I didn't find the MTU function
sctp_mtu_payload().

The problematic function that I found is sctp_setsockopt_maxseg()
located in the file net/sctp/socket.c.

Thanks,

Wenwen