tree c9d7063cbf17832a3b6a901042438eedceedb5c7
parent feef1866d1366d651e6a3cb8c9cf1a9aabb81395
author Christian Schoenebeck <qemu_oss@crudebyte.com> 1730802326 +0100
committer Christian Schoenebeck <qemu_oss@crudebyte.com> 1731058692 +0100

9pfs: fix crash on 'Treaddir' request

A bad (broken or malicious) 9p client (guest) could cause QEMU host to
crash by sending a 9p 'Treaddir' request with a numeric file ID (FID) that
was previously opened for a file instead of an expected directory:

  #0  0x0000762aff8f4919 in __GI___rewinddir (dirp=0xf) at
    ../sysdeps/unix/sysv/linux/rewinddir.c:29
  #1  0x0000557b7625fb40 in do_readdir_many (pdu=0x557bb67d2eb0,
    fidp=0x557bb67955b0, entries=0x762afe9fff58, offset=0, maxsize=131072,
    dostat=<optimized out>) at ../hw/9pfs/codir.c:101
  #2  v9fs_co_readdir_many (pdu=pdu@entry=0x557bb67d2eb0,
    fidp=fidp@entry=0x557bb67955b0, entries=entries@entry=0x762afe9fff58,
    offset=0, maxsize=131072, dostat=false) at ../hw/9pfs/codir.c:226
  #3  0x0000557b7625c1f9 in v9fs_do_readdir (pdu=0x557bb67d2eb0,
    fidp=0x557bb67955b0, offset=<optimized out>,
    max_count=<optimized out>) at ../hw/9pfs/9p.c:2488
  #4  v9fs_readdir (opaque=0x557bb67d2eb0) at ../hw/9pfs/9p.c:2602

That's because V9fsFidOpenState was declared as union type. So the
same memory region is used for either an open POSIX file handle (int),
or a POSIX DIR* pointer, etc., so 9p server incorrectly used the
previously opened (valid) POSIX file handle (0xf) as DIR* pointer,
eventually causing a crash in glibc's rewinddir() function.

Root cause was therefore a missing check in 9p server's 'Treaddir'
request handler, which must ensure that the client supplied FID was
really opened as directory stream before trying to access the
aforementioned union and its DIR* member.

Cc: qemu-stable@nongnu.org
Fixes: d62dbb51f7 ("virtio-9p: Add fidtype so that we can do type ...")
Reported-by: Akihiro Suda <suda.kyoto@gmail.com>
Tested-by: Akihiro Suda <suda.kyoto@gmail.com>
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <E1t8GnN-002RS8-E2@kylie.crudebyte.com>