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

[Greg Kurz]

On Mon, 12 Nov 2018 16:28:28 +0800
zhibin hu <address@hidden> wrote:

> 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

Ah, so we have a similar issue when creating files with the older
9p2000 and 9p2000.u protocols... I'll try to come up with a fix.

Cheers,

--
Greg

>     #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,
> >
> >