Re: [PATCH] sctp: don't dereference ptr before leaving _sctp_walk_{params,errors}()

[Alexander Potapenko]

On Thu, Jul 13, 2017 at 8:10 PM, Alexander Potapenko <glider@xxxxxxxxxx> wrote:
> If the iterator (|pos.p| or |err|) has already reached the end of
> chunk, we shouldn't access iterator->length.
>
> This bug has been detected by KMSAN. For the following pair of system
> calls:
>
>   socket(PF_INET6, SOCK_STREAM, 0x84 /* IPPROTO_??? */) = 3
>   sendto(3, "A", 1, MSG_OOB, {sa_family=AF_INET6, sin6_port=htons(0),
>          inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=0,
>          sin6_scope_id=0}, 28) = 1
>
> the tool has reported a use of uninitialized memory:
>
>   ==================================================================
>   BUG: KMSAN: use of uninitialized memory in sctp_rcv+0x17b8/0x43b0
>   CPU: 1 PID: 2940 Comm: probe Not tainted 4.11.0-rc5+ #2926
>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs
>   01/01/2011
>   Call Trace:
>    <IRQ>
>    __dump_stack lib/dump_stack.c:16
>    dump_stack+0x172/0x1c0 lib/dump_stack.c:52
>    kmsan_report+0x12a/0x180 mm/kmsan/kmsan.c:927
>    __msan_warning_32+0x61/0xb0 mm/kmsan/kmsan_instr.c:469
>    __sctp_rcv_init_lookup net/sctp/input.c:1074
>    __sctp_rcv_lookup_harder net/sctp/input.c:1233
>    __sctp_rcv_lookup net/sctp/input.c:1255
>    sctp_rcv+0x17b8/0x43b0 net/sctp/input.c:170
>    sctp6_rcv+0x32/0x70 net/sctp/ipv6.c:984
>    ip6_input_finish+0x82f/0x1ee0 net/ipv6/ip6_input.c:279
>    NF_HOOK ./include/linux/netfilter.h:257
>    ip6_input+0x239/0x290 net/ipv6/ip6_input.c:322
>    dst_input ./include/net/dst.h:492
>    ip6_rcv_finish net/ipv6/ip6_input.c:69
>    NF_HOOK ./include/linux/netfilter.h:257
>    ipv6_rcv+0x1dbd/0x22e0 net/ipv6/ip6_input.c:203
>    __netif_receive_skb_core+0x2f6f/0x3a20 net/core/dev.c:4208
>    __netif_receive_skb net/core/dev.c:4246
>    process_backlog+0x667/0xba0 net/core/dev.c:4866
>    napi_poll net/core/dev.c:5268
>    net_rx_action+0xc95/0x1590 net/core/dev.c:5333
>    __do_softirq+0x485/0x942 kernel/softirq.c:284
>    do_softirq_own_stack+0x1c/0x30 arch/x86/entry/entry_64.S:902
>    </IRQ>
>    do_softirq kernel/softirq.c:328
>    __local_bh_enable_ip+0x25b/0x290 kernel/softirq.c:181
>    local_bh_enable+0x37/0x40 ./include/linux/bottom_half.h:31
>    rcu_read_unlock_bh ./include/linux/rcupdate.h:931
>    ip6_finish_output2+0x19b2/0x1cf0 net/ipv6/ip6_output.c:124
>    ip6_finish_output+0x764/0x970 net/ipv6/ip6_output.c:149
>    NF_HOOK_COND ./include/linux/netfilter.h:246
>    ip6_output+0x456/0x520 net/ipv6/ip6_output.c:163
>    dst_output ./include/net/dst.h:486
>    NF_HOOK ./include/linux/netfilter.h:257
>    ip6_xmit+0x1841/0x1c00 net/ipv6/ip6_output.c:261
>    sctp_v6_xmit+0x3b7/0x470 net/sctp/ipv6.c:225
>    sctp_packet_transmit+0x38cb/0x3a20 net/sctp/output.c:632
>    sctp_outq_flush+0xeb3/0x46e0 net/sctp/outqueue.c:885
>    sctp_outq_uncork+0xb2/0xd0 net/sctp/outqueue.c:750
>    sctp_side_effects net/sctp/sm_sideeffect.c:1773
>    sctp_do_sm+0x6962/0x6ec0 net/sctp/sm_sideeffect.c:1147
>    sctp_primitive_ASSOCIATE+0x12c/0x160 net/sctp/primitive.c:88
>    sctp_sendmsg+0x43e5/0x4f90 net/sctp/socket.c:1954
>    inet_sendmsg+0x498/0x670 net/ipv4/af_inet.c:762
>    sock_sendmsg_nosec net/socket.c:633
>    sock_sendmsg net/socket.c:643
>    SYSC_sendto+0x608/0x710 net/socket.c:1696
>    SyS_sendto+0x8a/0xb0 net/socket.c:1664
>    do_syscall_64+0xe6/0x130 arch/x86/entry/common.c:285
>    entry_SYSCALL64_slow_path+0x25/0x25 arch/x86/entry/entry_64.S:246
>   RIP: 0033:0x401133
>   RSP: 002b:00007fff6d99cd38 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
>   RAX: ffffffffffffffda RBX: 00000000004002b0 RCX: 0000000000401133
>   RDX: 0000000000000001 RSI: 0000000000494088 RDI: 0000000000000003
>   RBP: 00007fff6d99cd90 R08: 00007fff6d99cd50 R09: 000000000000001c
>   R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
>   R13: 00000000004063d0 R14: 0000000000406460 R15: 0000000000000000
>   origin:
>    save_stack_trace+0x37/0x40 arch/x86/kernel/stacktrace.c:59
>    kmsan_save_stack_with_flags mm/kmsan/kmsan.c:302
>    kmsan_internal_poison_shadow+0xb1/0x1a0 mm/kmsan/kmsan.c:198
>    kmsan_poison_shadow+0x6d/0xc0 mm/kmsan/kmsan.c:211
>    slab_alloc_node mm/slub.c:2743
>    __kmalloc_node_track_caller+0x200/0x360 mm/slub.c:4351
>    __kmalloc_reserve net/core/skbuff.c:138
>    __alloc_skb+0x26b/0x840 net/core/skbuff.c:231
>    alloc_skb ./include/linux/skbuff.h:933
>    sctp_packet_transmit+0x31e/0x3a20 net/sctp/output.c:570
>    sctp_outq_flush+0xeb3/0x46e0 net/sctp/outqueue.c:885
>    sctp_outq_uncork+0xb2/0xd0 net/sctp/outqueue.c:750
>    sctp_side_effects net/sctp/sm_sideeffect.c:1773
>    sctp_do_sm+0x6962/0x6ec0 net/sctp/sm_sideeffect.c:1147
>    sctp_primitive_ASSOCIATE+0x12c/0x160 net/sctp/primitive.c:88
>    sctp_sendmsg+0x43e5/0x4f90 net/sctp/socket.c:1954
>    inet_sendmsg+0x498/0x670 net/ipv4/af_inet.c:762
>    sock_sendmsg_nosec net/socket.c:633
>    sock_sendmsg net/socket.c:643
>    SYSC_sendto+0x608/0x710 net/socket.c:1696
>    SyS_sendto+0x8a/0xb0 net/socket.c:1664
>    do_syscall_64+0xe6/0x130 arch/x86/entry/common.c:285
>    return_from_SYSCALL_64+0x0/0x6a arch/x86/entry/entry_64.S:246
>   ==================================================================
>
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> ---
>  include/net/sctp/sctp.h | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
> index a9519a06a23b..f13632ee33f0 100644
> --- a/include/net/sctp/sctp.h
> +++ b/include/net/sctp/sctp.h
> @@ -469,6 +469,7 @@ _sctp_walk_params((pos), (chunk), ntohs((chunk)->chunk_hdr.length), member)
>
>  #define _sctp_walk_params(pos, chunk, end, member)\
>  for (pos.v = chunk->member;\
> +     pos.v < (void *)chunk + end &&\
checkpatch.pl warns about spaces here, but I wanted to be consistent
with the rest of the file.
>       pos.v <= (void *)chunk + end - ntohs(pos.p->length) &&\
>       ntohs(pos.p->length) >= sizeof(struct sctp_paramhdr);\
>       pos.v += SCTP_PAD4(ntohs(pos.p->length)))
> @@ -479,6 +480,7 @@ _sctp_walk_errors((err), (chunk_hdr), ntohs((chunk_hdr)->length))
>  #define _sctp_walk_errors(err, chunk_hdr, end)\
>  for (err = (sctp_errhdr_t *)((void *)chunk_hdr + \
>             sizeof(struct sctp_chunkhdr));\
> +     (void *)err <= (void *)chunk_hdr + end &&\
>       (void *)err <= (void *)chunk_hdr + end - ntohs(err->length) &&\
>       ntohs(err->length) >= sizeof(sctp_errhdr_t); \
>       err = (sctp_errhdr_t *)((void *)err + SCTP_PAD4(ntohs(err->length))))
> --
> 2.13.2.932.g7449e964c-goog
>



-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
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