Re: [Qemu-devel] [PATCH] 9p: write lock path in v9fs_co_open2()

[zhibin hu]

hi,

i use this patch with qemu 3.0.0 and it seems not fix completely.

address@hidden ~]# ./qemu-system-x86_64 -snapshot -m 1024 -smp 2
-enable-kvm -net nic,model=e1000 -net
tap,helper=/usr/libexec/qemu-bridge-helper -hda
/var/lib/libvirt/images/test.qcow2 -fsdev
local,id=test_dev,path=/tmp,security_model=none -device
virtio-9p-pci,fsdev=test_dev,mount_tag=test_mount -vnc 0.0.0.0:1
==5014==WARNING: ASan doesn't fully support makecontext/swapcontext
functions and may produce false positives in some cases!
=================================================================
==5014==ERROR: AddressSanitizer: heap-use-after-free on address
0x60200014fc50 at pc 0x7f90c908697d bp 0x7f9053444970 sp 0x7f9053444118
READ of size 2 at 0x60200014fc50 thread T17
    #0 0x7f90c908697c  (/lib64/libasan.so.5+0x9997c)
    #1 0x7f90c8452693 in g_path_get_basename
(/lib64/libglib-2.0.so.0+0x39693)
    #2 0x559c1b78eb56 in local_lstat hw/9pfs/9p-local.c:182
    #3 0x559c1b799628 in v9fs_co_lstat hw/9pfs/cofile.c:53
    #4 0x559c1b777ee1 in fid_to_qid hw/9pfs/9p.c:598
    #5 0x559c1b77aeae in v9fs_attach hw/9pfs/9p.c:1017
    #6 0x559c1c145976 in coroutine_trampoline util/coroutine-ucontext.c:116
    #7 0x7f90bd6855ff in __correctly_grouped_prefixwc
(/lib64/libc.so.6+0x4c5ff)

0x60200014fc50 is located 0 bytes inside of 2-byte region
[0x60200014fc50,0x60200014fc52)
freed by thread T0 here:
    #0 0x7f90c90db880 in __interceptor_free (/lib64/libasan.so.5+0xee880)
    #1 0x7f90c846b4d1 in g_free (/lib64/libglib-2.0.so.0+0x524d1)
    #2 0x559c1b775ce4 in v9fs_path_copy hw/9pfs/9p.c:195
    #3 0x559c1b78425d in v9fs_create hw/9pfs/9p.c:2297
    #4 0x559c1c145976 in coroutine_trampoline util/coroutine-ucontext.c:116
    #5 0x7f90bd6855ff in __correctly_grouped_prefixwc
(/lib64/libc.so.6+0x4c5ff)

previously allocated by thread T4 here:
    #0 0x7f90c90dbc48 in malloc (/lib64/libasan.so.5+0xeec48)
    #1 0x7f90bd743c37 in __GI___vasprintf_chk (/lib64/libc.so.6+0x10ac37)

Thread T17 created by T16 here:
    #0 0x7f90c9038443 in pthread_create (/lib64/libasan.so.5+0x4b443)
    #1 0x559c1c10461e in qemu_thread_create util/qemu-thread-posix.c:534
    #2 0x559c1c0f2be4 in do_spawn_thread util/thread-pool.c:135
    #3 0x559c1c0f2498 in worker_thread util/thread-pool.c:83
    #4 0x559c1c1043e0 in qemu_thread_start util/qemu-thread-posix.c:504
    #5 0x7f90bd9ff593 in start_thread (/lib64/libpthread.so.0+0x7593)

Thread T16 created by T0 here:
    #0 0x7f90c9038443 in pthread_create (/lib64/libasan.so.5+0x4b443)
    #1 0x559c1c10461e in qemu_thread_create util/qemu-thread-posix.c:534
    #2 0x559c1c0f2be4 in do_spawn_thread util/thread-pool.c:135
    #3 0x559c1c0f2c73 in spawn_thread_bh_fn util/thread-pool.c:143
    #4 0x559c1c0ef4d0 in aio_bh_call util/async.c:90
    #5 0x559c1c0ef787 in aio_bh_poll util/async.c:118
    #6 0x559c1c0fb5bd in aio_dispatch util/aio-posix.c:436
    #7 0x559c1c0f026f in aio_ctx_dispatch util/async.c:261
    #8 0x7f90c84658ac in g_main_context_dispatch
(/lib64/libglib-2.0.so.0+0x4c8ac)

Thread T4 created by T0 here:
    #0 0x7f90c9038443 in pthread_create (/lib64/libasan.so.5+0x4b443)
    #1 0x559c1c10461e in qemu_thread_create util/qemu-thread-posix.c:534
    #2 0x559c1b2e7258 in qemu_kvm_start_vcpu /root/qemu-3.0.0/cpus.c:1935
    #3 0x559c1b2e7a0b in qemu_init_vcpu /root/qemu-3.0.0/cpus.c:2001
    #4 0x559c1b583f0c in x86_cpu_realizefn
/root/qemu-3.0.0/target/i386/cpu.c:4996
    #5 0x559c1b87f1e8 in device_set_realized hw/core/qdev.c:826
    #6 0x559c1bde6e62 in property_set_bool qom/object.c:1984
    #7 0x559c1bde2b0e in object_property_set qom/object.c:1176
    #8 0x559c1bde9b00 in object_property_set_qobject qom/qom-qobject.c:27
    #9 0x559c1bde2e2b in object_property_set_bool qom/object.c:1242
    #10 0x559c1b4f2452 in pc_new_cpu /root/qemu-3.0.0/hw/i386/pc.c:1107
    #11 0x559c1b4f2993 in pc_cpus_init /root/qemu-3.0.0/hw/i386/pc.c:1155
    #12 0x559c1b4fc9cb in pc_init1 /root/qemu-3.0.0/hw/i386/pc_piix.c:153
    #13 0x559c1b4fe81d in pc_init_v3_0
/root/qemu-3.0.0/hw/i386/pc_piix.c:438
    #14 0x559c1b890f29 in machine_run_board_init hw/core/machine.c:830
    #15 0x559c1b6d246e in main /root/qemu-3.0.0/vl.c:4516
    #16 0x7f90bd65c11a in __libc_start_main (/lib64/libc.so.6+0x2311a)

SUMMARY: AddressSanitizer: heap-use-after-free
(/lib64/libasan.so.5+0x9997c)
Shadow bytes around the buggy address:
  0x0c0480021f30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c0480021f40: fa fa fd fa fa fa fd fd fa fa fa fa fa fa fa fa
  0x0c0480021f50: fa fa fa fa fa fa fa fa fa fa fd fa fa fa fd fd
  0x0c0480021f60: fa fa fd fa fa fa fa fa fa fa fd fa fa fa fa fa
  0x0c0480021f70: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fd fa
=>0x0c0480021f80: fa fa fa fa fa fa fd fa fa fa[fd]fa fa fa fd fa
  0x0c0480021f90: fa fa fd fd fa fa fd fa fa fa fa fa fa fa fd fa
  0x0c0480021fa0: fa fa fd fa fa fa fd fa fa fa fd fa fa fa fa fa
  0x0c0480021fb0: fa fa fd fa fa fa fa fa fa fa fa fa fa fa fd fd
  0x0c0480021fc0: fa fa fd fa fa fa fa fa fa fa fa fa fa fa fd fa
  0x0c0480021fd0: fa fa fd fa fa fa fd fa fa fa fa fa fa fa fd fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==5014==ABORTING

thanks.

On Wed, Nov 7, 2018 at 8:21 AM Greg Kurz <address@hidden> wrote:

> The assumption that the fid cannot be used by any other operation is
> wrong. At least, nothing prevents a misbehaving client to create a
> file with a given fid, and to pass this fid to some other operation
> at the same time (ie, without waiting for the response to the creation
> request). The call to v9fs_path_copy() performed by the worker thread
> after the file was created can race with any access to the fid path
> performed by some other thread. This causes use-after-free issues that
> can be detected by ASAN with a custom 9p client.
>
> Unlike other operations that only read the fid path, v9fs_co_open2()
> does modify it. It should hence take the write lock.
>
> Cc: P J P <address@hidden>
> Reported-by: zhibin hu <address@hidden>
> Signed-off-by: Greg Kurz <address@hidden>
> ---
>  hw/9pfs/cofile.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/hw/9pfs/cofile.c b/hw/9pfs/cofile.c
> index 88791bc327ac..9c22837cda32 100644
> --- a/hw/9pfs/cofile.c
> +++ b/hw/9pfs/cofile.c
> @@ -140,10 +140,10 @@ int coroutine_fn v9fs_co_open2(V9fsPDU *pdu,
> V9fsFidState *fidp,
>      cred.fc_gid = gid;
>      /*
>       * Hold the directory fid lock so that directory path name
> -     * don't change. Read lock is fine because this fid cannot
> -     * be used by any other operation.
> +     * don't change. Take the write lock to be sure this fid
> +     * cannot be used by another operation.
>       */
> -    v9fs_path_read_lock(s);
> +    v9fs_path_write_lock(s);
>      v9fs_co_run_in_worker(
>          {
>              err = s->ops->open2(&s->ctx, &fidp->path,
>
>