Subject: Re: [PATCH V2] Fix memory leak in sctp_process_init

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Thu, 6 Jun 2019 12:47:55 -0300

On Wed, Jun 05, 2019 at 07:20:10AM -0400, Neil Horman wrote:
> On Wed, Jun 05, 2019 at 04:16:24AM +0800, Xin Long wrote:
> > On Tue, Jun 4, 2019 at 4:34 AM Neil Horman <[email-masked]> wrote:
> > >
> > > syzbot found the following leak in sctp_process_init
> > > 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
> > >     [<0000000044e11f96>] sctp_assoc_bh_rcv+0x13c/0x200
> > > net/sctp/associola.c:1074
> > >     [<00000000ec43804d>] sctp_inq_push+0x7f/0xb0 net/sctp/inqueue.c:95
> > >     [<00000000726aa954>] sctp_backlog_rcv+0x5e/0x2a0 net/sctp/input.c:354
> > >     [<00000000d9e249a8>] sk_backlog_rcv include/net/sock.h:950 [inline]
> > >     [<00000000d9e249a8>] __release_sock+0xab/0x110 net/core/sock.c:2418
> > >     [<00000000acae44fa>] release_sock+0x37/0xd0 net/core/sock.c:2934
> > >     [<00000000963cc9ae>] sctp_sendmsg+0x2c0/0x990 net/sctp/socket.c:2122
> > >     [<00000000a7fc7565>] inet_sendmsg+0x64/0x120 net/ipv4/af_inet.c:802
> > >     [<00000000b732cbd3>] sock_sendmsg_nosec net/socket.c:652 [inline]
> > >     [<00000000b732cbd3>] sock_sendmsg+0x54/0x70 net/socket.c:671
> > >     [<00000000274c57ab>] ___sys_sendmsg+0x393/0x3c0 net/socket.c:2292
> > >     [<000000008252aedb>] __sys_sendmsg+0x80/0xf0 net/socket.c:2330
> > >     [<00000000f7bf23d1>] __do_sys_sendmsg net/socket.c:2339 [inline]
> > >     [<00000000f7bf23d1>] __se_sys_sendmsg net/socket.c:2337 [inline]
> > >     [<00000000f7bf23d1>] __x64_sys_sendmsg+0x23/0x30 net/socket.c:2337
> > >     [<00000000a8b4131f>] do_syscall_64+0x76/0x1a0 arch/x86/entry/common.c:3
> > >
> > > The problem was that the peer.cookie value points to an skb allocated
> > > area on the first pass through this function, at which point it is
> > > overwritten with a heap allocated value, but in certain cases, where a
> > > COOKIE_ECHO chunk is included in the packet, a second pass through
> > > sctp_process_init is made, where the cookie value is re-allocated,
> > > leaking the first allocation.
> > This's not gonna happen, as after processing INIT, the temp asoc will be
> > deleted on the server side. Besides, from the reproducer:
> > 
> >   https://syzkaller.appspot.com/x/repro.syz?x=10e32f8ca00000
> > 
> > Packet(INIT|COOKIE_ECHO) can't be made in here.
> > 
> > The call trace says the leak happened when processing INIT_ACK on the
> > client side, as Marcelo noticed.  Then it can be triggered by:
> > 
> > 1. sctp_sf_do_5_1C_ack() -> SCTP_CMD_PEER_INIT -> sctp_process_init():
> >    where it "goto clean_up" after sctp_process_param(), but in 'cleanup'
> >    path, it doesn't do any freeup for the memdups of sctp_process_param().
> >    then the client T1 retrans INIT, and later get INIT_ACK again from the
> >    peer, and go to sctp_process_init() to memdup().
> > 
> > 2. sctp_sf_cookie_echoed_err() -> sctp_sf_do_5_2_6_stale():
> >    where the asoc state will go from COOKIE_ECHOED back to COOKIE_WAIT,
> >    and T1 starts to retrans INIT, and later it will get INIT_ACK again
> >    to sctp_process_init() and memdup().
> > 
> ok, you may well be right as to the path that we take to get here, but the root
> cause is the same, multiple passes through sctp_process_init without freeing the
> previously memduped memory.  Thats why I would think my patch is fixing the
> issue, because now we're always duping the cookie memory and always freeing it
> when we transition to the ESTABLISHED state.
> 
> As for the other variables (peer_[random|chunks|hmacs]), I'm not sure why we're
> not seeing leak reports of those variables.

This actually also works for peer.cookie as well, as now they are
allocated and freed in the same places.

I talked with Xin and I agree that this patch didn't really fix the
leak. It moved the allocation from sctp_process_init() to
sctp_process_param() which is called by sctp_process_init and there is
nothing avoiding multiple allocations on these vars once INIT_ACK is
retransmited.

The reproducer works by having the client to re-request cookies by
setting a short lifetime. So
Client sends INIT
                       Server replies INIT_ACK with cookie
Client echoes the cookie
                       Server rejects because the cookie expired
Client sends INIT again, to ask for another cookie
  (sctp_sf_do_5_2_6_stale)
                       Server sends INIT_ACK again with a new cookie
Client calls sctp_process_init again, from
  -> sctp_sf_do_5_1C_ack()
   -> sctp_cmd_process_init()
    -> sctp_process_init()
     -> sctp_process_param()
        ^-- leak happens
	               Server may or may not accept the new cookie,
		       leading to further leaks if not
(this is his 2nd case above)

Yet somehow the patch changed the dynamics and made the test pass (4x
10mins each run) here. Uff.

  Marcelo

> 
> Neil
> 
> > As on either above, asoc's never been to ESTABLISHED state,
> > asoc->peer.cookie can be not freed, and this patch won't work.
> > But yes, it's nice to have this patch, just not to fix this memleak.

+1 (read: won't hurt -stable and no need to revert)

> > 
> > I tracked the code, this memleak was triggered by case 2, so I think
> > you also need to add something like:
> > 
> > @@ -881,6 +893,18 @@ static void sctp_cmd_new_state(struct sctp_cmd_seq *cmds,
> >                                                 asoc->rto_initial;
> >                 asoc->timeouts[SCTP_EVENT_TIMEOUT_T1_COOKIE] =
> >                                                 asoc->rto_initial;
> > +
> > +               if (asoc->peer.cookie) {
> > +                       kfree(asoc->peer.cookie);
> > +                       kfree(asoc->peer.peer_random);
> > +                       kfree(asoc->peer.peer_chunks);
> > +                       kfree(asoc->peer.peer_hmacs);
> > +
> > +                       asoc->peer.cookie = NULL;
> > +                       asoc->peer.peer_random = NULL;
> > +                       asoc->peer.peer_random = NULL;
> > +                       asoc->peer.peer_hmacs = NULL;
> > +               }
> >         }
> > 
> > and the same thing may also be needed in sctp_cmd_process_init() on the
> > err path for case 1.
> > 
> > >
> > > Fix is to always allocate the cookie value, and free it when we are done
> > > using it.
> > >
> > > Signed-off-by: Neil Horman <[email-masked]>
> > > Reported-by: [email-masked]
> > > CC: Marcelo Ricardo Leitner <[email-masked]>
> > > CC: "David S. Miller" <[email-masked]>
> > > CC: [email-masked]
> > >
> > > ---
> > > Change notes
> > >
> > > V1->V2:
> > >   * Removed an accidental double free I let slip in in
> > > sctp_association_free
> > >   * Removed now unused cookie variable
> > > ---
> > >  net/sctp/sm_make_chunk.c | 13 +++----------
> > >  net/sctp/sm_sideeffect.c |  5 +++++
> > >  2 files changed, 8 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
> > > index 72e74503f9fc..8e12e19fe42d 100644
> > > --- a/net/sctp/sm_make_chunk.c
> > > +++ b/net/sctp/sm_make_chunk.c
> > > @@ -2327,7 +2327,6 @@ int sctp_process_init(struct sctp_association *asoc, struct sctp_chunk *chunk,
> > >         union sctp_addr addr;
> > >         struct sctp_af *af;
> > >         int src_match = 0;
> > > -       char *cookie;
> > >
> > >         /* We must include the address that the INIT packet came from.
> > >          * This is the only address that matters for an INIT packet.
> > > @@ -2431,14 +2430,6 @@ int sctp_process_init(struct sctp_association *asoc, struct sctp_chunk *chunk,
> > >         /* Peer Rwnd   : Current calculated value of the peer's rwnd.  */
> > >         asoc->peer.rwnd = asoc->peer.i.a_rwnd;
> > >
> > > -       /* Copy cookie in case we need to resend COOKIE-ECHO. */
> > > -       cookie = asoc->peer.cookie;
> > > -       if (cookie) {
> > > -               asoc->peer.cookie = kmemdup(cookie, asoc->peer.cookie_len, gfp);
> > > -               if (!asoc->peer.cookie)
> > > -                       goto clean_up;
> > > -       }
> > > -
> > >         /* RFC 2960 7.2.1 The initial value of ssthresh MAY be arbitrarily
> > >          * high (for example, implementations MAY use the size of the receiver
> > >          * advertised window).
> > > @@ -2607,7 +2598,9 @@ static int sctp_process_param(struct sctp_association *asoc,
> > >         case SCTP_PARAM_STATE_COOKIE:
> > >                 asoc->peer.cookie_len =
> > >                         ntohs(param.p->length) - sizeof(struct sctp_paramhdr);
> > > -               asoc->peer.cookie = param.cookie->body;
> > > +               asoc->peer.cookie = kmemdup(param.cookie->body, asoc->peer.cookie_len, gfp);
> > > +               if (!asoc->peer.cookie)
> > > +                       retval = 0;
> > >                 break;
> > >
> > >         case SCTP_PARAM_HEARTBEAT_INFO:
> > > diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
> > > index 4aa03588f87b..27ddf2d8f001 100644
> > > --- a/net/sctp/sm_sideeffect.c
> > > +++ b/net/sctp/sm_sideeffect.c
> > > @@ -898,6 +898,11 @@ static void sctp_cmd_new_state(struct sctp_cmd_seq *cmds,
> > >                                                 asoc->rto_initial;
> > >         }
> > >
> > > +       if (sctp_state(asoc, ESTABLISHED)) {
> > > +               kfree(asoc->peer.cookie);
> > > +               asoc->peer.cookie = NULL;
> > > +       }
> > > +
> > >         if (sctp_state(asoc, ESTABLISHED) ||
> > >             sctp_state(asoc, CLOSED) ||
> > >             sctp_state(asoc, SHUTDOWN_RECEIVED)) {
> > > --
> > > 2.20.1
> > >
> > 
>