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Message-ID: <20190529190709.GE31099@hmswarspite.think-freely.org>
Date: Wed, 29 May 2019 15:07:09 -0400
From: Neil Horman <nhorman@...driver.com>
To: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc: syzbot <syzbot+f7e9153b037eac9b1df8@...kaller.appspotmail.com>,
davem@...emloft.net, linux-kernel@...r.kernel.org,
linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
syzkaller-bugs@...glegroups.com, vyasevich@...il.com
Subject: Re: memory leak in sctp_process_init
On Tue, May 28, 2019 at 07:15:50AM -0400, Neil Horman wrote:
> On Mon, May 27, 2019 at 10:36:00PM -0300, Marcelo Ricardo Leitner wrote:
> > On Mon, May 27, 2019 at 05:48:06PM -0700, syzbot wrote:
> > > Hello,
> > >
> > > syzbot found the following crash on:
> > >
> > > HEAD commit: 9c7db500 Merge tag 'selinux-pr-20190521' of git://git.kern..
> > > git tree: upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=10388530a00000
> > > kernel config: https://syzkaller.appspot.com/x/.config?x=61dd9e15a761691d
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=f7e9153b037eac9b1df8
> > > compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10e32f8ca00000
> > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=177fa530a00000
> > >
> > > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > > Reported-by: syzbot+f7e9153b037eac9b1df8@...kaller.appspotmail.com
> > >
> > > 0 to HW filter on device batadv0
> > > executing program
> > > executing program
> > > executing program
> > > BUG: memory leak
> > > unreferenced object 0xffff88810ef68400 (size 1024):
> > > comm "syz-executor273", pid 7046, jiffies 4294945598 (age 28.770s)
> > > hex dump (first 32 bytes):
> > > 1d de 28 8d de 0b 1b e3 b5 c2 f9 68 fd 1a 97 25 ..(........h...%
> > > 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> > > backtrace:
> > > [<00000000a02cebbd>] kmemleak_alloc_recursive
> > > include/linux/kmemleak.h:55 [inline]
> > > [<00000000a02cebbd>] slab_post_alloc_hook mm/slab.h:439 [inline]
> > > [<00000000a02cebbd>] slab_alloc mm/slab.c:3326 [inline]
> > > [<00000000a02cebbd>] __do_kmalloc mm/slab.c:3658 [inline]
> > > [<00000000a02cebbd>] __kmalloc_track_caller+0x15d/0x2c0 mm/slab.c:3675
> > > [<000000009e6245e6>] kmemdup+0x27/0x60 mm/util.c:119
> > > [<00000000dfdc5d2d>] kmemdup include/linux/string.h:432 [inline]
> > > [<00000000dfdc5d2d>] sctp_process_init+0xa7e/0xc20
> > > net/sctp/sm_make_chunk.c:2437
> > > [<00000000b58b62f8>] sctp_cmd_process_init net/sctp/sm_sideeffect.c:682
> > > [inline]
> > > [<00000000b58b62f8>] sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1384
> > > [inline]
> > > [<00000000b58b62f8>] sctp_side_effects net/sctp/sm_sideeffect.c:1194
> > > [inline]
> > > [<00000000b58b62f8>] sctp_do_sm+0xbdc/0x1d60
> > > net/sctp/sm_sideeffect.c:1165
> >
> > Note that this is on the client side. It was handling the INIT_ACK
> > chunk, from sctp_sf_do_5_1C_ack().
> >
> > I'm not seeing anything else other than sctp_association_free()
> > releasing this memory. This means 2 things:
> > - Every time the cookie is retransmitted, it leaks. As shown by the
> > repetitive leaks here.
> > - The cookie remains allocated throughout the association, which is
> > also not good as that's a 1k that we could have released back to the
> > system right after the handshake.
> >
> > Marcelo
> >
> If we have an INIT chunk bundled with a COOKIE_ECHO chunk in the same packet,
> this might occur. Processing for each chunk (via sctp_cmd_process_init and
> sctp_sf_do_5_1D_ce both call sctp_process_init, which would cause a second write
> to asoc->peer.cookie, leaving the first write (set via kmemdup), to be orphaned
> and leak. Seems like we should set a flag to determine if we've already cloned
> the cookie, and free the old one if its set. If we wanted to do that on the
> cheap, we might be able to get away with checking asoc->stream->[in|out]cnt for
> being non-zero as an indicator if we've already cloned the cookie
>
> Neil
>
>
Completely untested, but can you give this patch a shot?
diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 0767701ef362..a5772d72eb87 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -1701,6 +1701,7 @@ struct sctp_association {
__u8 sack_needed:1, /* Do we need to sack the peer? */
sack_generation:1,
zero_window_announced:1;
+ cookie_allocated:1
__u32 sack_cnt;
__u32 adaptation_ind; /* Adaptation Code point. */
diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index 1999237ce481..b6e8fd7081b7 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -213,6 +213,7 @@ static struct sctp_association *sctp_association_init(
*/
asoc->peer.sack_needed = 1;
asoc->peer.sack_generation = 1;
+ asoc->cookie_allocated=0;
/* Assume that the peer will tell us if he recognizes ASCONF
* as part of INIT exchange.
diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
index 92331e1195c1..e966a3cc78bf 100644
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -2419,9 +2419,12 @@ int sctp_process_init(struct sctp_association *asoc, struct sctp_chunk *chunk,
/* Copy cookie in case we need to resend COOKIE-ECHO. */
cookie = asoc->peer.cookie;
if (cookie) {
+ if (asoc->peer.cookie_allocated)
+ kfree(cookie);
asoc->peer.cookie = kmemdup(cookie, asoc->peer.cookie_len, gfp);
if (!asoc->peer.cookie)
goto clean_up;
+ asoc->peer.cookie_allocated=1;
}
/* RFC 2960 7.2.1 The initial value of ssthresh MAY be arbitrarily
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