On Tue, Jun 4, 2019 at 4:34 AM Neil Horman <nhorman@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> > Reported-by: syzbot+f7e9153b037eac9b1df8@xxxxxxxxxxxxxxxxxxxxxxxxx > CC: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx> > CC: "David S. Miller" <davem@xxxxxxxxxxxxx> > CC: netdev@xxxxxxxxxxxxxxx > > --- > 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 >
