Re: [PULL 0/5] 9p queue 2022-02-10

[Greg Kurz]

On Mon, 14 Feb 2022 10:47:43 +0100
Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:

> On Sonntag, 13. Februar 2022 21:33:10 CET Peter Maydell wrote:
> > On Thu, 10 Feb 2022 at 11:33, Christian Schoenebeck
> > 
> > <qemu_oss@crudebyte.com> wrote:
> > > The following changes since commit 
> > > 0a301624c2f4ced3331ffd5bce85b4274fe132af:
> > >   Merge remote-tracking branch
> > >   'remotes/pmaydell/tags/pull-target-arm-20220208' into staging
> > >   (2022-02-08 11:40:08 +0000)> 
> > > are available in the Git repository at:
> > >   https://github.com/cschoenebeck/qemu.git tags/pull-9p-20220210
> > > 
> > > for you to fetch changes up to de19c79dad6a2cad54ae04ce754d47c07bf9bc93:
> > >   9pfs: Fix segfault in do_readdir_many caused by struct dirent overread
> > >   (2022-02-10 11:56:01 +0100)> 
> > > ----------------------------------------------------------------9d82f6a3e68c2
> > > 9pfs: fixes and cleanup
> > > 
> > > * Fifth patch fixes a 9pfs server crash that happened on some systems due
> > > 
> > >   to incorrect (system dependant) handling of struct dirent size.
> > > 
> > > * Tests: Second patch fixes a test error that happened on some systems due
> > > 
> > >   mkdir() being called twice for creating the test directory for the 9p
> > >   'local' tests.
> > > 
> > > * Tests: Third patch fixes a memory leak.
> > > 
> > > * Tests: The remaining two patches are code cleanup.
> > > 
> > > ----------------------------------------------------------------
> > 
> > Hi; this fails CI for the build-oss-fuzz job, which finds
> > a heap-buffer-overflow:
> > https://gitlab.com/qemu-project/qemu/-/jobs/2087610013
> 
> So this is about the 'dirent' patch:
> https://github.com/cschoenebeck/qemu/commit/de19c79dad6a2cad54ae04ce754d47c07bf9bc93
> 
> In conjunction with the 9p fuzzing tests:
> https://wiki.qemu.org/Documentation/9p#Fuzzing
> 
> I first thought it might be a false positive due to the unorthodox handling of
> dirent duplication by that patch, but from the ASan output below I am not
> really sure about that.
> 

No, this is an actual bug. See below.

> Is there a way to get the content of local variables?
> 
> Would it be possible that the following issue (g_memdup vs. g_memdup2) might
> apply here?
> https://discourse.gnome.org/t/port-your-module-from-g-memdup-to-g-memdup2-now/5538
> 
> Best regards,
> Christian Schoenebeck
> 
> > 
> > 8/152 qemu:qtest+qtest-i386 / qtest-i386/qos-test ERROR 66.74s killed
> > by signal 6 SIGABRT
> > 
> > >>> QTEST_QEMU_BINARY=./qemu-system-i386
> > >>> QTEST_QEMU_STORAGE_DAEMON_BINARY=./storage-daemon/qemu-storage-daemon
> > >>> MALLOC_PERTURB_=120
> > >>> G_TEST_DBUS_DAEMON=/builds/qemu-project/qemu/tests/dbus-vmstate-daemon.
> > >>> sh QTEST_QEMU_IMG=./qemu-img
> > >>> /builds/qemu-project/qemu/build-oss-fuzz/tests/qtest/qos-test --tap -k
> > ――――――――――――――――――――――――――――――――――――― ✀
> > ――――――――――――――――――――――――――――――――――――― Listing only the last 100 lines from
> > a long log.
> > For details see https://github.com/google/sanitizers/issues/189
> > ==7270==WARNING: ASan doesn't fully support makecontext/swapcontext
> > functions and may produce false positives in some cases!
> > ==7270==WARNING: ASan is ignoring requested __asan_handle_no_return:
> > stack type: default top: 0x7ffc79fb0000; bottom 0x7ff908ffd000; size:
> > 0x000370fb3000 (14780411904)
> > False positive error reports may follow
> > For details see https://github.com/google/sanitizers/issues/189
> > ==7276==WARNING: ASan doesn't fully support makecontext/swapcontext
> > functions and may produce false positives in some cases!
> > ==7276==WARNING: ASan is ignoring requested __asan_handle_no_return:
> > stack type: default top: 0x7fff7e4a8000; bottom 0x7fd6363fd000; size:
> > 0x0029480ab000 (177302319104)
> > False positive error reports may follow
> > For details see https://github.com/google/sanitizers/issues/189
> > ==7282==WARNING: ASan doesn't fully support makecontext/swapcontext
> > functions and may produce false positives in some cases!
> > ==7282==WARNING: ASan is ignoring requested __asan_handle_no_return:
> > stack type: default top: 0x7ffee6e7f000; bottom 0x7f32fb5fd000; size:
> > 0x00cbeb882000 (875829927936)
> > False positive error reports may follow
> > For details see https://github.com/google/sanitizers/issues/189
> > ==7288==WARNING: ASan doesn't fully support makecontext/swapcontext
> > functions and may produce false positives in some cases!
> > ==7288==WARNING: ASan is ignoring requested __asan_handle_no_return:
> > stack type: default top: 0x7ffc6118e000; bottom 0x7f6391cfd000; size:
> > 0x0098cf491000 (656312700928)
> > False positive error reports may follow
> > For details see https://github.com/google/sanitizers/issues/189
> > ==7294==WARNING: ASan doesn't fully support makecontext/swapcontext
> > functions and may produce false positives in some cases!
> > ==7294==WARNING: ASan is ignoring requested __asan_handle_no_return:
> > stack type: default top: 0x7ffef665d000; bottom 0x7f69dc8fd000; size:
> > 0x009519d60000 (640383582208)
> > False positive error reports may follow
> > For details see https://github.com/google/sanitizers/issues/189
> > ==7300==WARNING: ASan doesn't fully support makecontext/swapcontext
> > functions and may produce false positives in some cases!
> > ==7300==WARNING: ASan is ignoring requested __asan_handle_no_return:
> > stack type: default top: 0x7ffe33db0000; bottom 0x7f01421fd000; size:
> > 0x00fcf1bb3000 (1086387335168)
> > False positive error reports may follow
> > For details see https://github.com/google/sanitizers/issues/189
> > ==7306==WARNING: ASan doesn't fully support makecontext/swapcontext
> > functions and may produce false positives in some cases!
> > ==7306==WARNING: ASan is ignoring requested __asan_handle_no_return:
> > stack type: default top: 0x7ffebd618000; bottom 0x7ff1179fd000; size:
> > 0x000da5c1b000 (58615508992)
> > False positive error reports may follow
> > For details see https://github.com/google/sanitizers/issues/189
> > =================================================================
> > ==7306==ERROR: AddressSanitizer: heap-buffer-overflow on address
> > 0x612000030768 at pc 0x562351066c74 bp 0x7ff1078c3a90 sp
> > 0x7ff1078c3240
> > READ of size 48830 at 0x612000030768 thread T4

The size looks pretty big to me. Test file paths in virtio-9p-test are
only a couple of bytes long...

> > #0 0x562351066c73 in __interceptor_memcpy.part.0 asan_interceptors.cpp.o
> > #1 0x7ff1290d443f in g_memdup (/lib64/libglib-2.0.so.0+0x6e43f)
> > #2 0x56235134537a in do_readdir_many
> > /builds/qemu-project/qemu/build-oss-fuzz/../hw/9pfs/codir.c:146:19
> > #3 0x56235134537a in v9fs_co_readdir_many
> > /builds/qemu-project/qemu/build-oss-fuzz/../hw/9pfs/codir.c:225:5
> > #4 0x56235132d626 in v9fs_do_readdir
> > /builds/qemu-project/qemu/build-oss-fuzz/../hw/9pfs/9p.c:2430:13
> > #5 0x56235132d626 in v9fs_readdir
> > /builds/qemu-project/qemu/build-oss-fuzz/../hw/9pfs/9p.c:2543:13
> > #6 0x56235257101e in coroutine_trampoline
> > /builds/qemu-project/qemu/build-oss-fuzz/../util/coroutine-ucontext.c:173:9
> > #7 0x7ff126e0e84f (/lib64/libc.so.6+0x5784f)
> > 0x612000030768 is located 0 bytes to the right of 296-byte region
> > [0x612000030640,0x612000030768)
> > allocated by thread T4 here:
> > #0 0x5623510a4e47 in malloc
> > (/builds/qemu-project/qemu/build-oss-fuzz/qemu-system-i386+0x1146e47)
> > #1 0x7ff1290c03d8 in g_malloc (/lib64/libglib-2.0.so.0+0x5a3d8)

i.e.

    synth_open = g_malloc(sizeof(*synth_open));

and we have:

typedef struct V9fsSynthOpenState {
    off_t offset;
    V9fsSynthNode *node;
    struct dirent dent;
} V9fsSynthOpenState;

It looks like that qemu_dirent_dup() ends up using an
uninitialized dent->d_reclen.

The synth backend should be fixed to honor d_reclen, or
at least to allocate with g_new0().

Cheers,

--
Greg

> > #2 0x56235131e659 in synth_opendir
> > /builds/qemu-project/qemu/build-oss-fuzz/../hw/9pfs/9p-synth.c:185:18
> > #3 0x5623513462f5 in v9fs_co_opendir
> > /builds/qemu-project/qemu/build-oss-fuzz/../hw/9pfs/codir.c:321:5
> > #4 0x5623513257d7 in v9fs_open
> > /builds/qemu-project/qemu/build-oss-fuzz/../hw/9pfs/9p.c:1959:15
> > #5 0x56235257101e in coroutine_trampoline
> > /builds/qemu-project/qemu/build-oss-fuzz/../util/coroutine-ucontext.c:173:9
> > #6 0x7ff126e0e84f (/lib64/libc.so.6+0x5784f)
> > Thread T4 created by T0 here:
> > #0 0x562351015926 in pthread_create
> > (/builds/qemu-project/qemu/build-oss-fuzz/qemu-system-i386+0x10b7926)
> > #1 0x5623525351ea in qemu_thread_create
> > /builds/qemu-project/qemu/build-oss-fuzz/../util/qemu-thread-posix.c:596:11
> > #2 0x5623525a4588 in do_spawn_thread
> > /builds/qemu-project/qemu/build-oss-fuzz/../util/thread-pool.c:134:5
> > #3 0x5623525a4588 in spawn_thread_bh_fn
> > /builds/qemu-project/qemu/build-oss-fuzz/../util/thread-pool.c:142:5
> > #4 0x562352569814 in aio_bh_call
> > /builds/qemu-project/qemu/build-oss-fuzz/../util/async.c:141:5
> > #5 0x562352569814 in aio_bh_poll
> > /builds/qemu-project/qemu/build-oss-fuzz/../util/async.c:169:13
> > #6 0x5623525248cc in aio_dispatch
> > /builds/qemu-project/qemu/build-oss-fuzz/../util/aio-posix.c:415:5
> > #7 0x56235256c34c in aio_ctx_dispatch
> > /builds/qemu-project/qemu/build-oss-fuzz/../util/async.c:311:5
> > #8 0x7ff1290bb05e in g_main_context_dispatch
> > (/lib64/libglib-2.0.so.0+0x5505e) SUMMARY: AddressSanitizer:
> > heap-buffer-overflow
> > asan_interceptors.cpp.o in __interceptor_memcpy.part.0
> > Shadow bytes around the buggy address:
> > 0x0c247fffe090: fa fa fa fa fa fa fa fa fd fd fd fd fd fd fd fd
> > 0x0c247fffe0a0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
> > 0x0c247fffe0b0: fd fd fd fd fd fd fd fd fd fd fd fd fd fa fa fa
> > 0x0c247fffe0c0: fa fa fa fa fa fa fa fa 00 00 00 00 00 00 00 00
> > 0x0c247fffe0d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > =>0x0c247fffe0e0: 00 00 00 00 00 00 00 00 00 00 00 00 00[fa]fa fa
> > 0x0c247fffe0f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
> > 0x0c247fffe100: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
> > 0x0c247fffe110: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
> > 0x0c247fffe120: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
> > 0x0c247fffe130: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 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
> > ==7306==ABORTING
> > 
> > 
> > thanks
> > -- PMM
> 
>