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    Subject[PATCH 3.16 068/294] sctp: don't dereference ptr before leaving _sctp_walk_{params, errors}()
    3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Alexander Potapenko <glider@google.com>

    commit b1f5bfc27a19f214006b9b4db7b9126df2dfdf5a upstream.

    If the length field of the iterator (|pos.p| or |err|) is past the end
    of the chunk, we shouldn't access it.

    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@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    [bwh: Backported to 3.16: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    include/net/sctp/sctp.h | 4 ++++
    1 file changed, 4 insertions(+)

    --- a/include/net/sctp/sctp.h
    +++ b/include/net/sctp/sctp.h
    @@ -448,6 +448,8 @@ _sctp_walk_params((pos), (chunk), ntohs(

    #define _sctp_walk_params(pos, chunk, end, member)\
    for (pos.v = chunk->member;\
    + (pos.v + offsetof(struct sctp_paramhdr, length) + sizeof(pos.p->length) <\
    + (void *)chunk + end) &&\
    pos.v <= (void *)chunk + end - ntohs(pos.p->length) &&\
    ntohs(pos.p->length) >= sizeof(sctp_paramhdr_t);\
    pos.v += WORD_ROUND(ntohs(pos.p->length)))
    @@ -458,6 +460,8 @@ _sctp_walk_errors((err), (chunk_hdr), nt
    #define _sctp_walk_errors(err, chunk_hdr, end)\
    for (err = (sctp_errhdr_t *)((void *)chunk_hdr + \
    sizeof(sctp_chunkhdr_t));\
    + ((void *)err + offsetof(sctp_errhdr_t, length) + sizeof(err->length) <\
    + (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 + WORD_ROUND(ntohs(err->length))))
    \
     
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