use-after-free in ip6_xmit

[Dmitry Vyukov]

Hello,

The following program triggers use-after-free in ip6_xmit:

// autogenerated by syzkaller (http://github.com/google/syzkaller)
#include <syscall.h>
#include <string.h>
#include <stdint.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <linux/socket.h>
#include <linux/in.h>
#include <linux/in6.h>
#include <unistd.h>
#include <stdlib.h>

void *thr0(void *arg)
{
        *(uint32_t*)0x20000000 = 0x5;
        long r5 = syscall(SYS_setsockopt, arg, 0x29ul, 0x6ul,
0x20000000ul, 0x4ul, 0);
        return 0;
}

void *thr1(void *arg)
{
        struct sockaddr_in6 sa = {};
        sa.sin6_family = AF_INET6;
        sa.sin6_port = getpid();
        sa.sin6_addr.s6_addr[15] = 1;
        syscall(SYS_bind, arg, &sa, sizeof(sa), 0, 0, 0);
        return 0;
}

void *thr2(void *arg)
{
        struct sockaddr_in6 sa = {};
        sa.sin6_family = AF_INET6;
        sa.sin6_port = getpid();
        sa.sin6_addr.s6_addr[15] = 1;
        syscall(SYS_connect, arg, &sa, sizeof(sa), 0, 0, 0);
        return 0;
}

void *thr3(void *arg)
{
        syscall(SYS_listen, arg, 0x3ul, 0, 0, 0, 0);
        return 0;
}

void *thr4(void *arg)
{
        syscall(SYS_accept4, arg, 0, 0, 0x800ul, 0, 0);
        return 0;
}

int main()
{
        srand(getpid());
        syscall(SYS_mmap, 0x20000000ul, 0x10000ul, 0x2ul, 0x32ul,
0xfffffffffffffffful, 0x0ul);
        int fd[2];
        fd[0] = syscall(SYS_socket, PF_INET6, SOCK_STREAM, IPPROTO_TCP);
        fd[1] = syscall(SYS_socket, PF_INET6, SOCK_STREAM, IPPROTO_TCP);
        pthread_t th;
        pthread_create(&th, 0, thr0, (void*)(long)fd[0]);
        pthread_create(&th, 0, thr1, (void*)(long)fd[0]);
        pthread_create(&th, 0, thr2, (void*)(long)fd[0]);
        pthread_create(&th, 0, thr3, (void*)(long)fd[0]);
        pthread_create(&th, 0, thr4, (void*)(long)fd[0]);
        pthread_create(&th, 0, thr0, (void*)(long)fd[0]);
        pthread_create(&th, 0, thr1, (void*)(long)fd[0]);
        pthread_create(&th, 0, thr2, (void*)(long)fd[0]);
        pthread_create(&th, 0, thr3, (void*)(long)fd[0]);
        pthread_create(&th, 0, thr4, (void*)(long)fd[0]);
        pthread_create(&th, 0, thr0, (void*)(long)fd[1]);
        pthread_create(&th, 0, thr1, (void*)(long)fd[1]);
        pthread_create(&th, 0, thr2, (void*)(long)fd[1]);
        pthread_create(&th, 0, thr3, (void*)(long)fd[1]);
        pthread_create(&th, 0, thr4, (void*)(long)fd[1]);
        pthread_create(&th, 0, thr0, (void*)(long)fd[1]);
        pthread_create(&th, 0, thr1, (void*)(long)fd[1]);
        pthread_create(&th, 0, thr2, (void*)(long)fd[1]);
        pthread_create(&th, 0, thr3, (void*)(long)fd[1]);
        pthread_create(&th, 0, thr4, (void*)(long)fd[1]);

        usleep(20000);
        return 0;
}



==================================================================
BUG: KASAN: use-after-free in ip6_xmit+0x15e3/0x1f50 at addr ffff88003991c786
Read of size 2 by task a.out/6864
=============================================================================
BUG kmalloc-64 (Not tainted): kasan: bad access detected
-----------------------------------------------------------------------------

Disabling lock debugging due to kernel taint
INFO: Allocated in sock_kmalloc+0x93/0x100 age=40 cpu=1 pid=6850
[<      none      >] ___slab_alloc+0x648/0x8c0 mm/slub.c:2438
[<      none      >] __slab_alloc+0x4c/0x90 mm/slub.c:2467
[<     inline     >] slab_alloc_node mm/slub.c:2530
[<     inline     >] slab_alloc mm/slub.c:2572
[<      none      >] __kmalloc+0x2d9/0x480 mm/slub.c:3532
[<     inline     >] kmalloc include/linux/slab.h:463
[<      none      >] sock_kmalloc+0x93/0x100 net/core/sock.c:1772
[<      none      >] do_ipv6_setsockopt.isra.5+0xf4d/0x2d30
net/ipv6/ipv6_sockglue.c:483
[<      none      >] ipv6_setsockopt+0x4f/0x150 net/ipv6/ipv6_sockglue.c:885
[<      none      >] sctp_setsockopt+0x194/0x4020 net/sctp/socket.c:3702
[<      none      >] sock_common_setsockopt+0xb4/0x140 net/core/sock.c:2643
[<     inline     >] SYSC_setsockopt net/socket.c:1757
[<      none      >] SyS_setsockopt+0x161/0x290 net/socket.c:1736
[<      none      >] entry_SYSCALL_64_fastpath+0x16/0x7a
arch/x86/entry/entry_64.S:185

INFO: Freed in sock_kfree_s+0x29/0x90 age=34 cpu=0 pid=6855
[<      none      >] __slab_free+0x21e/0x3e0 mm/slub.c:2648
[<     inline     >] slab_free mm/slub.c:2803
[<      none      >] kfree+0x26f/0x3e0 mm/slub.c:3632
[<     inline     >] __sock_kfree_s net/core/sock.c:1793
[<      none      >] sock_kfree_s+0x29/0x90 net/core/sock.c:1799
[<      none      >] do_ipv6_setsockopt.isra.5+0x100f/0x2d30
net/ipv6/ipv6_sockglue.c:506
[<      none      >] ipv6_setsockopt+0x4f/0x150 net/ipv6/ipv6_sockglue.c:885
[<      none      >] sctp_setsockopt+0x194/0x4020 net/sctp/socket.c:3702
[<      none      >] sock_common_setsockopt+0xb4/0x140 net/core/sock.c:2643
[<     inline     >] SYSC_setsockopt net/socket.c:1757
[<      none      >] SyS_setsockopt+0x161/0x290 net/socket.c:1736
[<      none      >] entry_SYSCALL_64_fastpath+0x16/0x7a
arch/x86/entry/entry_64.S:185

INFO: Slab 0xffffea0000e64700 objects=21 used=19 fp=0xffff88003991cc00
flags=0x1fffc0000004080
INFO: Object 0xffff88003991c780 @offset=1920 fp=0x          (null)
CPU: 2 PID: 6864 Comm: a.out Tainted: G    B           4.4.0-rc3+ #150
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
 0000000000000002 ffff88005f3f6e18 ffffffff82c6f2a8 0000000041b58ab3
 ffffffff8788bf8d ffffffff82c6f1f6 ffff880062045a00 ffffffff878ac723
 ffff88003e807700 0000000000000008 ffff88003991c780 ffff88005f3f6e18

Call Trace:
 [<     inline     >] __dump_stack lib/dump_stack.c:15
 [<ffffffff82c6f2a8>] dump_stack+0xb2/0xfa lib/dump_stack.c:50
 [<ffffffff81788e3c>] print_trailer+0x12c/0x210 mm/slub.c:652
 [<ffffffff81793c5f>] object_err+0x2f/0x40 mm/slub.c:659
 [<     inline     >] print_address_description mm/kasan/report.c:138
 [<ffffffff817979c9>] kasan_report_error+0x5d9/0x860 mm/kasan/report.c:251
 [<     inline     >] kasan_report mm/kasan/report.c:274
 [<ffffffff81797d14>] __asan_report_load2_noabort+0x54/0x70
mm/kasan/report.c:293
 [<ffffffff85bc06e3>] ip6_xmit+0x15e3/0x1f50 net/ipv6/ip6_output.c:176
 [<ffffffff8635a0b9>] sctp_v6_xmit+0x319/0x530 net/sctp/ipv6.c:223
 [<ffffffff8634595d>] sctp_packet_transmit+0x113d/0x2680 net/sctp/output.c:595
 [<ffffffff8630e897>] sctp_outq_flush+0x717/0x2840 net/sctp/outqueue.c:1090
 [<ffffffff86315d67>] sctp_outq_uncork+0x57/0x80 net/sctp/outqueue.c:692
 [<     inline     >] sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1750
 [<     inline     >] sctp_side_effects net/sctp/sm_sideeffect.c:1153
 [<ffffffff862d9e83>] sctp_do_sm+0x38a3/0x5be0 net/sctp/sm_sideeffect.c:1125
 [<ffffffff863423c9>] sctp_primitive_SHUTDOWN+0xa9/0xd0 net/sctp/primitive.c:104
 [<ffffffff8632e94d>] sctp_close+0x6fd/0x9b0 net/sctp/socket.c:1519
 [<ffffffff85a4b2a1>] inet_release+0x111/0x270 net/ipv4/af_inet.c:413
 [<ffffffff85bac8c5>] inet6_release+0x55/0x90 net/ipv6/af_inet6.c:406
 [<ffffffff85501586>] sock_release+0x96/0x260 net/socket.c:571
 [<ffffffff85501766>] sock_close+0x16/0x20 net/socket.c:1022
 [<ffffffff817f0014>] __fput+0x244/0x860 fs/file_table.c:208
 [<ffffffff817f06c5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8133a5e0>] task_work_run+0x130/0x240 kernel/task_work.c:115
 [<     inline     >] exit_task_work include/linux/task_work.h:21
 [<ffffffff812d4a05>] do_exit+0x885/0x3050 kernel/exit.c:750
 [<ffffffff812d732c>] do_group_exit+0xec/0x390 kernel/exit.c:880
 [<ffffffff81302177>] get_signal+0x677/0x1bf0 kernel/signal.c:2307
 [<ffffffff8118645e>] do_signal+0x7e/0x2170 arch/x86/kernel/signal.c:709
 [<ffffffff81003a1e>] exit_to_usermode_loop+0xfe/0x1e0
arch/x86/entry/common.c:247
 [<     inline     >] prepare_exit_to_usermode arch/x86/entry/common.c:282
 [<ffffffff8100733b>] syscall_return_slowpath+0x16b/0x240
arch/x86/entry/common.c:344
 [<ffffffff868dafe2>] int_ret_from_sys_call+0x25/0x9f
arch/x86/entry/entry_64.S:281
==================================================================

On commit 31ade3b83e1821da5fbb2f11b5b3d4ab2ec39db8.

The allocation/free stacks look similar to the ones I reported in
"memory leak in do_ipv6_setsockopt". However, the fix for that leak
suggests that it could lead only to leaks, not to use-after-frees.
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