Re: [PATCH v4] 9pfs: Fix segfault in do_readdir_many caused by struct dirent overread

[Christian Schoenebeck <qemu_oss@crudebyte.com>]

On Sonntag, 6. Februar 2022 02:34:19 CET Vitaly Chikunov wrote:
> `struct dirent' returned from readdir(3) could be shorter (or longer)
> 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>
> Reviewed-by: Dmitry V. Levin <ldv@altlinux.org>
> Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
> ---
> Tested on x68-64 Linux with btrfs-progs tests and slow qos-test.
> Changes since v3:
> - Update commentary on qemu_dirent_dup logic.
> - Use g_memdup as suggested by Greg Kurz.
> 
>  hw/9pfs/codir.c      |  3 +--
>  include/qemu/osdep.h | 13 +++++++++++++
>  util/osdep.c         | 21 +++++++++++++++++++++
>  3 files changed, 35 insertions(+), 2 deletions(-)

Queued on 9p.next:
https://github.com/cschoenebeck/qemu/commits/9p.next

Thanks!

I plan to send a PR with my current queue to Peter tomorrow.

Best regards,
Christian Schoenebeck