Message-ID: <CAG_fn=VYn-QNoyfvQKOynAR0cyJx+Sczvyh8Gk0SukEgYMmAVw@mail.gmail.com>
Date:   Mon, 14 Jan 2019 10:34:11 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        syzbot+ad5d327e6936a2e284be@...kaller.appspotmail.com,
        davem <davem@...emloft.net>, LKML <linux-kernel@...r.kernel.org>,
        linux-sctp@...r.kernel.org, network dev <netdev@...r.kernel.org>,
        Neil Horman <nhorman@...driver.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Vlad Yasevich <vyasevich@...il.com>
Subject: Re: KMSAN: kernel-infoleak in sctp_getsockopt

On Mon, Dec 10, 2018 at 9:56 AM Xin Long <lucien.xin@...il.com> wrote:
>
> On Thu, Dec 6, 2018 at 8:08 PM Marcelo Ricardo Leitner
> <marcelo.leitner@...il.com> wrote:
> >
> > On Thu, Dec 06, 2018 at 11:36:08AM +0100, Alexander Potapenko wrote:
> > > On Wed, Dec 5, 2018 at 8:31 PM syzbot
> > > <syzbot+ad5d327e6936a2e284be@...kaller.appspotmail.com> wrote:
> > > >
> > > > 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+ad5d327e6936a2e284be@...kaller.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
> > > > ==================================================================
> > > 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.
> >
> > Agree. Thanks Alexander.
> > Looks like this is the last/only place left with this issue.
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;


> 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;
>
> >
> > > >
> > > > ---
> > > > 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 syzkaller@...glegroups.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-bugs+unsubscribe@...glegroups.com.
> > > > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/000000000000311344057c4b6cc3%40google.com.
> > > > 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
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

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