Re: use-after-free in sock_wake_async

[Eric Dumazet]

On Tue, Nov 24, 2015 at 6:18 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> Hello,
>
> The following program triggers use-after-free in sock_wake_async:
>
> // autogenerated by syzkaller (http://github.com/google/syzkaller)
> #include <syscall.h>
> #include <string.h>
> #include <stdint.h>
> #include <pthread.h>
>
> long r2 = -1;
> long r3 = -1;
> long r7 = -1;
>
> void *thr0(void *arg)
> {
>         syscall(SYS_splice, r2, 0x0ul, r7, 0x0ul, 0x4ul, 0x8ul);
>         return 0;
> }
>
> void *thr1(void *arg)
> {
>         syscall(SYS_close, r2, 0, 0, 0, 0, 0);
>         return 0;
> }
>
> void *thr2(void *arg)
> {
>         syscall(SYS_write, r3, 0x20003000ul, 0xe7ul, 0, 0, 0);
>         return 0;
> }
>
> int main()
> {
>         long r0 = syscall(SYS_mmap, 0x20000000ul, 0x10000ul, 0x3ul,
> 0x32ul, 0xfffffffffffffffful, 0x0ul);
>         long r1 = syscall(SYS_socketpair, 0x1ul, 0x1ul, 0x0ul,
> 0x20000000ul, 0, 0);
>         r2 = *(uint32_t*)0x20000000;
>         r3 = *(uint32_t*)0x20000004;
>
>         *(uint64_t*)0x20001000 = 0x4;
>         long r5 = syscall(SYS_ioctl, r2, 0x5452ul, 0x20001000ul, 0, 0, 0);
>
>         long r6 = syscall(SYS_pipe2, 0x20002000ul, 0x80800ul, 0, 0, 0, 0);
>         r7 = *(uint32_t*)0x20002004;
>
>         pthread_t th[3];
>         pthread_create(&th[0], 0, thr0, 0);
>         pthread_create(&th[1], 0, thr1, 0);
>         pthread_create(&th[2], 0, thr2, 0);
>         pthread_join(th[0], 0);
>         pthread_join(th[1], 0);
>         pthread_join(th[2], 0);
>         return 0;
> }
>
>
> The use-after-free fires after a minute of running it in a tight
> parallel loop. I use the stress utility for this:
>
> $ go get golang.org/x/tools/cmd/stress
> $ stress -p 128 -failure "ignore" ./a.out
>
>
> ==================================================================
> BUG: KASAN: use-after-free in sock_wake_async+0x325/0x340 at addr
> ffff880061d1ad10
> Read of size 8 by task a.out/23178
> =============================================================================
> BUG sock_inode_cache (Not tainted): kasan: bad access detected
> -----------------------------------------------------------------------------
>
> Disabling lock debugging due to kernel taint
> INFO: Allocated in sock_alloc_inode+0x1d/0x220 age=0 cpu=2 pid=23183
> [<      none      >] kmem_cache_alloc+0x1a6/0x1f0 mm/slub.c:2514
> [<      none      >] sock_alloc_inode+0x1d/0x220 net/socket.c:250
> [<      none      >] alloc_inode+0x61/0x180 fs/inode.c:198
> [<      none      >] new_inode_pseudo+0x17/0xe0 fs/inode.c:878
> [<      none      >] sock_alloc+0x3d/0x260 net/socket.c:540
> [<      none      >] __sock_create+0xa7/0x620 net/socket.c:1133
> [<     inline     >] sock_create net/socket.c:1209
> [<     inline     >] SYSC_socketpair net/socket.c:1281
> [<      none      >] SyS_socketpair+0x112/0x4e0 net/socket.c:1260
> [<      none      >] entry_SYSCALL_64_fastpath+0x16/0x7a
> arch/x86/entry/entry_64.S:185
>
> INFO: Freed in sock_destroy_inode+0x56/0x70 age=0 cpu=2 pid=23185
> [<      none      >] kmem_cache_free+0x24e/0x260 mm/slub.c:2742
> [<      none      >] sock_destroy_inode+0x56/0x70 net/socket.c:279
> [<      none      >] destroy_inode+0xc4/0x120 fs/inode.c:255
> [<      none      >] evict+0x36b/0x580 fs/inode.c:559
> [<     inline     >] iput_final fs/inode.c:1477
> [<      none      >] iput+0x4a0/0x790 fs/inode.c:1504
> [<     inline     >] dentry_iput fs/dcache.c:358
> [<      none      >] __dentry_kill+0x4fe/0x700 fs/dcache.c:543
> [<     inline     >] dentry_kill fs/dcache.c:587
> [<      none      >] dput+0x6ab/0x7a0 fs/dcache.c:796
> [<      none      >] __fput+0x3fb/0x6e0 fs/file_table.c:226
> [<      none      >] ____fput+0x15/0x20 fs/file_table.c:244
> [<      none      >] task_work_run+0x163/0x1f0 kernel/task_work.c:115
> (discriminator 1)
> [<     inline     >] tracehook_notify_resume include/linux/tracehook.h:191
> [<      none      >] exit_to_usermode_loop+0x180/0x1a0
> arch/x86/entry/common.c:251
> [<     inline     >] prepare_exit_to_usermode arch/x86/entry/common.c:282
> [<      none      >] syscall_return_slowpath+0x19f/0x210
> arch/x86/entry/common.c:344
> [<      none      >] int_ret_from_sys_call+0x25/0x9f
> arch/x86/entry/entry_64.S:281
>
> INFO: Slab 0xffffea0001874600 objects=25 used=2 fp=0xffff880061d1c100
> flags=0x500000000004080
> INFO: Object 0xffff880061d1ad00 @offset=11520 fp=0xffff880061d1a300
> CPU: 3 PID: 23178 Comm: a.out Tainted: G    B           4.4.0-rc1+ #84
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>  00000000ffffffff ffff880061baf8f0 ffffffff825d3336 ffff88003e0dc280
>  ffff880061d1ad00 ffff880061d18000 ffff880061baf920 ffffffff81618784
>  ffff88003e0dc280 ffffea0001874600 ffff880061d1ad00 00000000000000e7
>
> Call Trace:
>  [<ffffffff8162135e>] __asan_report_load8_noabort+0x3e/0x40
> mm/kasan/report.c:280
>  [<     inline     >] __read_once_size include/linux/compiler.h:218
>  [<ffffffff83dcda05>] sock_wake_async+0x325/0x340 net/socket.c:1068
>  [<     inline     >] sk_wake_async include/net/sock.h:2011
>  [<ffffffff83ddb414>] sock_def_readable+0x1e4/0x290 net/core/sock.c:2312
>  [<ffffffff84188bdb>] unix_stream_sendmsg+0x4db/0x930 net/unix/af_unix.c:1864
>  [<     inline     >] sock_sendmsg_nosec net/socket.c:610
>  [<ffffffff83dcb1fa>] sock_sendmsg+0xca/0x110 net/socket.c:620
>  [<ffffffff83dcb456>] sock_write_iter+0x216/0x3a0 net/socket.c:819
>  [<     inline     >] new_sync_write fs/read_write.c:478
>  [<ffffffff8165d310>] __vfs_write+0x300/0x470 fs/read_write.c:491
>  [<ffffffff8165e4fe>] vfs_write+0x16e/0x490 fs/read_write.c:538
>  [<     inline     >] SYSC_write fs/read_write.c:585
>  [<ffffffff81661141>] SyS_write+0x111/0x220 fs/read_write.c:577
>  [<ffffffff84bf0c36>] entry_SYSCALL_64_fastpath+0x16/0x7a
> arch/x86/entry/entry_64.S:185
> ==================================================================
>
>
> I am on commit 8005c49d9aea74d382f474ce11afbbc7d7130bec (Nov 15) but
> also merged in 7d267278a9ece963d77eefec61630223fce08c6c (unix: avoid
> use-after-free in ep_remove_wait_queue) from net repo.
>
> Thanks

Looks like commit 830a1e5c212fb3fdc83b66359c780c3b3a294897 should be reverted ?

commit 830a1e5c212fb3fdc83b66359c780c3b3a294897
Author: Benjamin LaHaise <benjamin.c.lahaise@xxxxxxxxx>
Date:   Tue Dec 13 23:22:32 2005 -0800

    [AF_UNIX]: Remove superfluous reference counting in unix_stream_sendmsg

    AF_UNIX stream socket performance on P4 CPUs tends to suffer due to a
    lot of pipeline flushes from atomic operations.  The patch below
    removes the sock_hold() and sock_put() in unix_stream_sendmsg().  This
    should be safe as the socket still holds a reference to its peer which
    is only released after the file descriptor's final user invokes
    unix_release_sock().  The only consideration is that we must add a
    memory barrier before setting the peer initially.

    Signed-off-by: Benjamin LaHaise <benjamin.c.lahaise@xxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
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