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

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Tue, 4 Jun 2019 17:59:04 -0300

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().
> 
> 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.
> 
> I tracked the code, this memleak was triggered by case 2, so I think
> you also need to add something like:

Interesting, because as part of writing some scripts here to more
easily work with syzkaller reports, I actually had the patch Neil
posted being tested on Friday and with it applied the reproducer
didn't catch any leaks anymore, while with it, it takes a while but
the leaks were happening.

(Will read the details you posted later, I'm just sharing this for
now, sorry for the rushiness)

> 
> @@ -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
> >
>