[PATCH v2] sctp: don't dereference ptr before leaving _sctp_walk_{params,errors}()
From: Alexander Potapenko
Date: Fri Jul 14 2017 - 06:05:10 EST
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@xxxxxxxxxx>
---
v2: per comment from David Miller, make sure the whole iterator->length
fits into the remaining buffer.
---
include/net/sctp/sctp.h | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
index a9519a06a23b..9f6164a15715 100644
--- a/include/net/sctp/sctp.h
+++ b/include/net/sctp/sctp.h
@@ -469,6 +469,8 @@ _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 + offsetof(sctp_paramhdr_t, length) + sizeof(pos.p->length) <\
+ (void *)chunk + end) &&\
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 +481,8 @@ _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 + 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 + SCTP_PAD4(ntohs(err->length))))
--
2.13.2.932.g7449e964c-goog