[Bug 1883083] [NEW] QEMU: block/vvfat driver issues

[P J P]

Public bug reported:

Nathan Huckleberry <nhuck15@gmail.com> has reported following issues in
the block/vvfat driver for the virtual VFAT file system image, used to
share a host system directory with a guest VM.

Please note:
  -> https://www.qemu.org/docs/master/system/images.html#virtual-fat-disk-images

Virtual VFAT read/write support is available only for (beta) testing
purposes.

Following issues are reproducible with:

   host)$ ./bin/qemu-system-x86_64 -nographic -enable-kvm \
              -drive file=fat:rw:/tmp/var/run/,index=2  -m 2048 
/var/lib/libvirt/images/f27vm.qcow2

  guest)# mount -t vfat /dev/sdb1 /mnt/

The attached reproducers (run inside a guest) include:

1. dir.sh: - directory traversal on the host
   - It creates a file under /mnt/yyyy
   - Then edits the VFAT directory entry to make it -> /mnt/../y
   - The handle_renames_and_mkdirs() routine does not check this new file name
     and creates a file outside of the shared directory on the host

2. dos.sh: hits an assertion failure in vvfat driver
   - Creates a deep directory tree like - /mnt/0/1/2/3/4/5/6/../29/30/
   - While updating vvfat commits, driver hits an assertion in
     handle_renames_and_mkdirs
       ...
       } else if (commit->action == ACTION_MKDIR) {
           ...
           assert(j < s->mapping.next);    <== it fails

3. read.sh: reads past vvfat directory entries
   - Creates a file with: echo "x" > /mnt/a
   - Reads past VVFAT directory entry structure with

       # head -c 1000000 $MNTDEV | xxd | grep x -A 512

   - It may disclose some heap addresses.

4. write.sh: heap buffer overflow
   - Creates large number of files as /mnt/file[1..35]
   - while syncing directory tree with the host, driver hits an overflow
     while doing memmove(3) in array_roll() routine

** Affects: qemu
     Importance: Undecided
         Status: New


** Tags: qemu

** Attachment added: "vvfat-reproducers-shared-by-Nathan"
   
https://bugs.launchpad.net/bugs/1883083/+attachment/5382870/+files/vvfat-issues.tar.xz

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https://bugs.launchpad.net/bugs/1883083

Title:
  QEMU: block/vvfat driver issues

Status in QEMU:
  New

Bug description:
  Nathan Huckleberry <nhuck15@gmail.com> has reported following issues
  in the block/vvfat driver for the virtual VFAT file system image, used
  to share a host system directory with a guest VM.

  Please note:
    -> 
https://www.qemu.org/docs/master/system/images.html#virtual-fat-disk-images

  Virtual VFAT read/write support is available only for (beta) testing
  purposes.

  Following issues are reproducible with:

     host)$ ./bin/qemu-system-x86_64 -nographic -enable-kvm \
                -drive file=fat:rw:/tmp/var/run/,index=2  -m 2048 
/var/lib/libvirt/images/f27vm.qcow2

    guest)# mount -t vfat /dev/sdb1 /mnt/

  The attached reproducers (run inside a guest) include:

  1. dir.sh: - directory traversal on the host
     - It creates a file under /mnt/yyyy
     - Then edits the VFAT directory entry to make it -> /mnt/../y
     - The handle_renames_and_mkdirs() routine does not check this new file name
       and creates a file outside of the shared directory on the host

  2. dos.sh: hits an assertion failure in vvfat driver
     - Creates a deep directory tree like - /mnt/0/1/2/3/4/5/6/../29/30/
     - While updating vvfat commits, driver hits an assertion in
       handle_renames_and_mkdirs
         ...
         } else if (commit->action == ACTION_MKDIR) {
             ...
             assert(j < s->mapping.next);    <== it fails

  3. read.sh: reads past vvfat directory entries
     - Creates a file with: echo "x" > /mnt/a
     - Reads past VVFAT directory entry structure with

         # head -c 1000000 $MNTDEV | xxd | grep x -A 512

     - It may disclose some heap addresses.

  4. write.sh: heap buffer overflow
     - Creates large number of files as /mnt/file[1..35]
     - while syncing directory tree with the host, driver hits an overflow
       while doing memmove(3) in array_roll() routine

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