[PATCH net] sctp: Avoid out-of-bounds reads from address storage

From: Stefano Brivio
Date: Wed Aug 23 2017 - 07:29:21 EST

inet_diag_msg_sctp{,l}addr_fill() and sctp_get_sctp_info() copy
sizeof(sockaddr_storage) bytes to fill in sockaddr structs used
to export diagnostic information to userspace.

However, the memory allocated to store sockaddr information is
smaller than that and depends on the address family, so we leak
up to 100 uninitialized bytes to userspace. Just use the size of
the source structs instead, in all the three cases this is what
userspace expects. Zero out the remaining memory.

Unused bytes (i.e. when IPv4 addresses are used) in source
structs sctp_sockaddr_entry and sctp_transport are already
cleared by sctp_add_bind_addr() and sctp_transport_new(),
respectively.

Noticed while testing KASAN-enabled kernel with 'ss':

[ 2326.885243] BUG: KASAN: slab-out-of-bounds in inet_sctp_diag_fill+0x42c/0x6c0 [sctp_diag] at addr ffff881be8779800
[ 2326.896800] Read of size 128 by task ss/9527
[ 2326.901564] CPU: 0 PID: 9527 Comm: ss Not tainted 4.11.0-22.el7a.x86_64 #1
[ 2326.909236] Hardware name: Dell Inc. PowerEdge R730/072T6D, BIOS 2.4.3 01/17/2017
[ 2326.917585] Call Trace:
[ 2326.920312] dump_stack+0x63/0x8d
[ 2326.924014] kasan_object_err+0x21/0x70
[ 2326.928295] kasan_report+0x288/0x540
[ 2326.932380] ? inet_sctp_diag_fill+0x42c/0x6c0 [sctp_diag]
[ 2326.938500] ? skb_put+0x8b/0xd0
[ 2326.942098] ? memset+0x31/0x40
[ 2326.945599] check_memory_region+0x13c/0x1a0
[ 2326.950362] memcpy+0x23/0x50
[ 2326.953669] inet_sctp_diag_fill+0x42c/0x6c0 [sctp_diag]
[ 2326.959596] ? inet_diag_msg_sctpasoc_fill+0x460/0x460 [sctp_diag]
[ 2326.966495] ? __lock_sock+0x102/0x150
[ 2326.970671] ? sock_def_wakeup+0x60/0x60
[ 2326.975048] ? remove_wait_queue+0xc0/0xc0
[ 2326.979619] sctp_diag_dump+0x44a/0x760 [sctp_diag]
[ 2326.985063] ? sctp_ep_dump+0x280/0x280 [sctp_diag]
[ 2326.990504] ? memset+0x31/0x40
[ 2326.994007] ? mutex_lock+0x12/0x40
[ 2326.997900] __inet_diag_dump+0x57/0xb0 [inet_diag]
[ 2327.003340] ? __sys_sendmsg+0x150/0x150
[ 2327.007715] inet_diag_dump+0x4d/0x80 [inet_diag]
[ 2327.012979] netlink_dump+0x1e6/0x490
[ 2327.017064] __netlink_dump_start+0x28e/0x2c0
[ 2327.021924] inet_diag_handler_cmd+0x189/0x1a0 [inet_diag]
[ 2327.028045] ? inet_diag_rcv_msg_compat+0x1b0/0x1b0 [inet_diag]
[ 2327.034651] ? inet_diag_dump_compat+0x190/0x190 [inet_diag]
[ 2327.040965] ? __netlink_lookup+0x1b9/0x260
[ 2327.045631] sock_diag_rcv_msg+0x18b/0x1e0
[ 2327.050199] netlink_rcv_skb+0x14b/0x180
[ 2327.054574] ? sock_diag_bind+0x60/0x60
[ 2327.058850] sock_diag_rcv+0x28/0x40
[ 2327.062837] netlink_unicast+0x2e7/0x3b0
[ 2327.067212] ? netlink_attachskb+0x330/0x330
[ 2327.071975] ? kasan_check_write+0x14/0x20
[ 2327.076544] netlink_sendmsg+0x5be/0x730
[ 2327.080918] ? netlink_unicast+0x3b0/0x3b0
[ 2327.085486] ? kasan_check_write+0x14/0x20
[ 2327.090057] ? selinux_socket_sendmsg+0x24/0x30
[ 2327.095109] ? netlink_unicast+0x3b0/0x3b0
[ 2327.099678] sock_sendmsg+0x74/0x80
[ 2327.103567] ___sys_sendmsg+0x520/0x530
[ 2327.107844] ? __get_locked_pte+0x178/0x200
[ 2327.112510] ? copy_msghdr_from_user+0x270/0x270
[ 2327.117660] ? vm_insert_page+0x360/0x360
[ 2327.122133] ? vm_insert_pfn_prot+0xb4/0x150
[ 2327.126895] ? vm_insert_pfn+0x32/0x40
[ 2327.131077] ? vvar_fault+0x71/0xd0
[ 2327.134968] ? special_mapping_fault+0x69/0x110
[ 2327.140022] ? __do_fault+0x42/0x120
[ 2327.144008] ? __handle_mm_fault+0x1062/0x17a0
[ 2327.148965] ? __fget_light+0xa7/0xc0
[ 2327.153049] __sys_sendmsg+0xcb/0x150
[ 2327.157133] ? __sys_sendmsg+0xcb/0x150
[ 2327.161409] ? SyS_shutdown+0x140/0x140
[ 2327.165688] ? exit_to_usermode_loop+0xd0/0xd0
[ 2327.170646] ? __do_page_fault+0x55d/0x620
[ 2327.175216] ? __sys_sendmsg+0x150/0x150
[ 2327.179591] SyS_sendmsg+0x12/0x20
[ 2327.183384] do_syscall_64+0xe3/0x230
[ 2327.187471] entry_SYSCALL64_slow_path+0x25/0x25
[ 2327.192622] RIP: 0033:0x7f41d18fa3b0
[ 2327.196608] RSP: 002b:00007ffc3b731218 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
[ 2327.205055] RAX: ffffffffffffffda RBX: 00007ffc3b731380 RCX: 00007f41d18fa3b0
[ 2327.213017] RDX: 0000000000000000 RSI: 00007ffc3b731340 RDI: 0000000000000003
[ 2327.220978] RBP: 0000000000000002 R08: 0000000000000004 R09: 0000000000000040
[ 2327.228939] R10: 00007ffc3b730f30 R11: 0000000000000246 R12: 0000000000000003
[ 2327.236901] R13: 00007ffc3b731340 R14: 00007ffc3b7313d0 R15: 0000000000000084
[ 2327.244865] Object at ffff881be87797e0, in cache kmalloc-64 size: 64
[ 2327.251953] Allocated:
[ 2327.254581] PID = 9484
[ 2327.257215] save_stack_trace+0x1b/0x20
[ 2327.261485] save_stack+0x46/0xd0
[ 2327.265179] kasan_kmalloc+0xad/0xe0
[ 2327.269165] kmem_cache_alloc_trace+0xe6/0x1d0
[ 2327.274138] sctp_add_bind_addr+0x58/0x180 [sctp]
[ 2327.279400] sctp_do_bind+0x208/0x310 [sctp]
[ 2327.284176] sctp_bind+0x61/0xa0 [sctp]
[ 2327.288455] inet_bind+0x5f/0x3a0
[ 2327.292151] SYSC_bind+0x1a4/0x1e0
[ 2327.295944] SyS_bind+0xe/0x10
[ 2327.299349] do_syscall_64+0xe3/0x230
[ 2327.303433] return_from_SYSCALL_64+0x0/0x6a
[ 2327.308194] Freed:
[ 2327.310434] PID = 4131
[ 2327.313065] save_stack_trace+0x1b/0x20
[ 2327.317344] save_stack+0x46/0xd0
[ 2327.321040] kasan_slab_free+0x73/0xc0
[ 2327.325220] kfree+0x96/0x1a0
[ 2327.328530] dynamic_kobj_release+0x15/0x40
[ 2327.333195] kobject_release+0x99/0x1e0
[ 2327.337472] kobject_put+0x38/0x70
[ 2327.341266] free_notes_attrs+0x66/0x80
[ 2327.345545] mod_sysfs_teardown+0x1a5/0x270
[ 2327.350211] free_module+0x20/0x2a0
[ 2327.354099] SyS_delete_module+0x2cb/0x2f0
[ 2327.358667] do_syscall_64+0xe3/0x230
[ 2327.362750] return_from_SYSCALL_64+0x0/0x6a
[ 2327.367510] Memory state around the buggy address:
[ 2327.372855] ffff881be8779700: fc fc fc fc 00 00 00 00 00 00 00 00 fc fc fc fc
[ 2327.380914] ffff881be8779780: fb fb fb fb fb fb fb fb fc fc fc fc 00 00 00 00
[ 2327.388972] >ffff881be8779800: 00 00 00 00 fc fc fc fc fb fb fb fb fb fb fb fb
[ 2327.397031] ^
[ 2327.401792] ffff881be8779880: fc fc fc fc fb fb fb fb fb fb fb fb fc fc fc fc
[ 2327.409850] ffff881be8779900: 00 00 00 00 00 04 fc fc fc fc fc fc 00 00 00 00
[ 2327.417907] ==================================================================

This fixes CVE-2017-7558.

References: https://bugzilla.redhat.com/show_bug.cgi?id=1480266
Fixes: 8f840e47f190 ("sctp: add the sctp_diag.c file")
Cc: <stable@xxxxxxxxxxxxxxx> # 4.7+
Cc: Xin Long <lucien.xin@xxxxxxxxx>
Cc: Vlad Yasevich <vyasevich@xxxxxxxxx>
Cc: Neil Horman <nhorman@xxxxxxxxxxxxx>
Signed-off-by: Stefano Brivio <sbrivio@xxxxxxxxxx>
---
net/sctp/sctp_diag.c | 7 +++++--
net/sctp/socket.c | 3 +--
2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/sctp/sctp_diag.c b/net/sctp/sctp_diag.c
index 9a647214a91e..e99518e79b52 100644
--- a/net/sctp/sctp_diag.c
+++ b/net/sctp/sctp_diag.c
@@ -70,7 +70,8 @@ static int inet_diag_msg_sctpladdrs_fill(struct sk_buff *skb,

info = nla_data(attr);
list_for_each_entry_rcu(laddr, address_list, list) {
- memcpy(info, &laddr->a, addrlen);
+ memcpy(info, &laddr->a, sizeof(laddr->a));
+ memset(info + sizeof(laddr->a), 0, addrlen - sizeof(laddr->a));
info += addrlen;
}

@@ -93,7 +94,9 @@ static int inet_diag_msg_sctpaddrs_fill(struct sk_buff *skb,
info = nla_data(attr);
list_for_each_entry(from, &asoc->peer.transport_addr_list,
transports) {
- memcpy(info, &from->ipaddr, addrlen);
+ memcpy(info, &from->ipaddr, sizeof(from->ipaddr));
+ memset(info + sizeof(from->ipaddr), 0,
+ addrlen - sizeof(from->ipaddr));
info += addrlen;
}

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 1db478e34520..8d760863bc41 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -4538,8 +4538,7 @@ int sctp_get_sctp_info(struct sock *sk, struct sctp_association *asoc,
info->sctpi_ictrlchunks = asoc->stats.ictrlchunks;

prim = asoc->peer.primary_path;
- memcpy(&info->sctpi_p_address, &prim->ipaddr,
- sizeof(struct sockaddr_storage));
+ memcpy(&info->sctpi_p_address, &prim->ipaddr, sizeof(prim->ipaddr));
info->sctpi_p_state = prim->state;
info->sctpi_p_cwnd = prim->cwnd;
info->sctpi_p_srtt = prim->srtt;
--
2.9.4