Re: [PATCH v2] 9pfs: Fix segfault in do_readdir_many caused by struct dirent overread

[Vitaly Chikunov]

Christian,

On Wed, Feb 02, 2022 at 05:55:45PM +0100, Christian Schoenebeck wrote:
> On Freitag, 28. Januar 2022 23:33:26 CET Vitaly Chikunov wrote:
> > `struct dirent' returned from readdir(3) could be shorter than
> > `sizeof(struct dirent)', thus memcpy of sizeof length will overread
> > into unallocated page causing SIGSEGV. Example stack trace:
> > 
> >  #0  0x00005555559ebeed v9fs_co_readdir_many (/usr/bin/qemu-system-x86_64 +
> > 0x497eed) #1  0x00005555559ec2e9 v9fs_readdir (/usr/bin/qemu-system-x86_64
> > + 0x4982e9) #2  0x0000555555eb7983 coroutine_trampoline
> > (/usr/bin/qemu-system-x86_64 + 0x963983) #3  0x00007ffff73e0be0 n/a (n/a +
> > 0x0)
> > 
> > While fixing, provide a helper for any future `struct dirent' cloning.
> > 
> > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841
> > Cc: qemu-stable@nongnu.org
> > Co-authored-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
> > Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
> > ---
> > Tested on x86-64 Linux.
> 
> I was too optimistic. Looks like this needs more work. With this patch applied
> the 9p test cases [1] are crashing now:
> 
> $ gdb --args tests/qtest/qos-test -m slow
> ...
> # Start of flush tests
> ok 50 
> /x86_64/pc/i440FX-pcihost/pci-bus-pc/pci-bus/virtio-9p-pci/virtio-9p/virtio-9p-tests/synth/flush/success
> ok 51 
> /x86_64/pc/i440FX-pcihost/pci-bus-pc/pci-bus/virtio-9p-pci/virtio-9p/virtio-9p-tests/synth/flush/ignored
> # End of flush tests
> # Start of readdir tests

I changed implementation from the one using dent->d_reclen to the one using
strlen(dent->d_name) and it's passed readdir tests, but failed later:

  # Start of readdir tests
  ok 53 
/x86_64/pc/i440FX-pcihost/pci-bus-pc/pci-bus/virtio-9p-pci/virtio-9p/virtio-9p-tests/synth/readdir/basic
  ok 54 
/x86_64/pc/i440FX-pcihost/pci-bus-pc/pci-bus/virtio-9p-pci/virtio-9p/virtio-9p-tests/synth/readdir/split_512
  ok 55 
/x86_64/pc/i440FX-pcihost/pci-bus-pc/pci-bus/virtio-9p-pci/virtio-9p/virtio-9p-tests/synth/readdir/split_256
  ok 56 
/x86_64/pc/i440FX-pcihost/pci-bus-pc/pci-bus/virtio-9p-pci/virtio-9p/virtio-9p-tests/synth/readdir/split_128
  # End of readdir tests
  # End of synth tests
  # Start of local tests
  # starting QEMU: exec x86_64-softmmu/qemu-system-x86_64 -qtest 
unix:/tmp/qtest-2822967.sock -qtest-log /dev/null -chardev 
socket,path=/tmp/qtest-2822967.qmp,id=char0 -mon chardev=char0,mode=control 
-display none -M pc  -fsdev 
local,id=fsdev0,path='/usr/src/RPM/BUILD/qemu-6.2.0/build-dynamic/qtest-9p-local-NpcZCR',security_model=mapped-xattr
 -device virtio-9p-pci,fsdev=fsdev0,addr=04.0,mount_tag=qtest -accel qtest
  # GLib-DEBUG: setenv()/putenv() are not thread-safe and should not be used 
after threads are created
  ok 57 
/x86_64/pc/i440FX-pcihost/pci-bus-pc/pci-bus/virtio-9p-pci/virtio-9p/virtio-9p-tests/local/config
  Received response 7 (RLERROR) instead of 73 (RMKDIR)
  Rlerror has errno 95 (Operation not supported)
  **
  ERROR:../tests/qtest/virtio-9p-test.c:305:v9fs_req_recv: assertion failed 
(hdr.id == id): (7 == 73)
  Bail out! ERROR:../tests/qtest/virtio-9p-test.c:305:v9fs_req_recv: assertion 
failed (hdr.id == id): (7 == 73)
  Aborted

Thanks,

> Broken pipe
> 
> Thread 1 "qos-test" received signal SIGABRT, Aborted.
> __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
> 50      ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
> (gdb) bt
> #0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
> #1  0x00007ffff7b7d537 in __GI_abort () at abort.c:79
> #2  0x00005555555ba495 in qtest_client_socket_recv_line (s=0x5555557663c0) at 
> ../tests/qtest/libqtest.c:503
> #3  0x00005555555ba5b3 in qtest_rsp_args (s=0x5555557663c0, expected_args=2) 
> at ../tests/qtest/libqtest.c:523
> #4  0x00005555555bbdb4 in qtest_clock_rsp (s=0x5555557663c0) at 
> ../tests/qtest/libqtest.c:970
> #5  0x00005555555bbe55 in qtest_clock_step (s=0x5555557663c0, step=100) at 
> ../tests/qtest/libqtest.c:985
> #6  0x00005555555cdc21 in qvirtio_wait_used_elem (qts=0x5555557663c0, 
> d=0x555555779b48, vq=0x5555557b0480, desc_idx=8, len=0x0, timeout_us=10000000)
>     at ../tests/qtest/libqos/virtio.c:220
> #7  0x00005555555ae79f in v9fs_req_wait_for_reply (req=0x5555557899a0, 
> len=0x0) at ../tests/qtest/virtio-9p-test.c:278
> #8  0x00005555555b03bf in fs_readdir (obj=0x555555779bb0, data=0x0, 
> t_alloc=0x5555557448b8) at ../tests/qtest/virtio-9p-test.c:851
> #9  0x00005555555990c4 in run_one_test (arg=0x5555557ac600) at 
> ../tests/qtest/qos-test.c:182
> #10 0x00007ffff7f02b9e in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
> #11 0x00007ffff7f0299b in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
> #12 0x00007ffff7f0299b in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
> #13 0x00007ffff7f0299b in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
> #14 0x00007ffff7f0299b in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
> #15 0x00007ffff7f0299b in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
> #16 0x00007ffff7f0299b in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
> #17 0x00007ffff7f0299b in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
> #18 0x00007ffff7f0299b in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
> #19 0x00007ffff7f0299b in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
> #20 0x00007ffff7f0299b in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
> #21 0x00007ffff7f0308a in g_test_run_suite () from 
> /lib/x86_64-linux-gnu/libglib-2.0.so.0
> #22 0x00007ffff7f030a1 in g_test_run () from 
> /lib/x86_64-linux-gnu/libglib-2.0.so.0
> #23 0x00005555555995a3 in main (argc=1, argv=0x7fffffffe508, 
> envp=0x7fffffffe528) at ../tests/qtest/qos-test.c:338
> (gdb)
> 
> [1] https://wiki.qemu.org/Documentation/9p#Test_Cases
> 
> Best regards,
> Christian Schoenebeck
> 
>