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Date: Wed, 5 Jun 2019 04:16:24 +0800
From: Xin Long <lucien.xin@...il.com>
To: Neil Horman <nhorman@...driver.com>
Cc: linux-sctp@...r.kernel.org,
syzbot+f7e9153b037eac9b1df8@...kaller.appspotmail.com,
Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
"David S. Miller" <davem@...emloft.net>,
network dev <netdev@...r.kernel.org>
Subject: Re: [PATCH V2] Fix memory leak in sctp_process_init
On Tue, Jun 4, 2019 at 4:34 AM Neil Horman <nhorman@...driver.com> 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:
@@ -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 <nhorman@...driver.com>
> Reported-by: syzbot+f7e9153b037eac9b1df8@...kaller.appspotmail.com
> CC: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
> CC: "David S. Miller" <davem@...emloft.net>
> CC: netdev@...r.kernel.org
>
> ---
> 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
>
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