git: DragonFly_RELEASE_4_4 sys/vfs/hammer: Fix bug on erasing volume header

[Tomohiro Kusumi]

commit c34b9df50c3d8107955d628046b82e924e54bac8
Author: Tomohiro Kusumi <kusumi.tomohiro at gmail.com>
Date:   Sun Mar 20 18:09:28 2016 +0900

    sys/vfs/hammer: Fix bug on erasing volume header
    
    deabdbfb in 2015 had a bug in hammer volume-del ioctl which didn't
    completely erase the volume header. hammer_ioc_volume_del() needed
    to declare an ondisk volume variable instead of a pointer.
    
    Having a pointer here caused bzero against the pointer itself
    (within kernel stack of hammer volume-del), and then clear ondisk
    volume header using kernel stack image.
    
    The following [A] shows the volume deleted by hammer volume-del
    has kernel stack itself for sizeof(struct hammer_volume_ondisk) bytes
    which is 1928 bytes. It should be like [B] where 0-1928 bytes are
    zero filled. [A] actually happens to erase the filesystem signature
    (HAMMER_FSBUF_VOLUME) located at the first 8 bytes of the header
    since it equals pointer size in x86_64, but it needs to properly
    zero clear the whole header (1928 bytes) for security reason.
    
      [A] Before this commit
      # newfs_hammer -L TEST /dev/da2 > /dev/null
      # mount_hammer /dev/da2 /HAMMER
      # hammer volume-add /dev/da3 /HAMMER
      # hammer volume-del /dev/da3 /HAMMER
      # od -tx1 -N 1928 /dev/da3
      0000000    00  00  00  00  00  00  00  00  40  4d  31  23  e1  ff  ff  ff
      0000020    00  00  00  00  00  00  00  00  00  44  2a  52  e0  ff  ff  ff
      0000040    40  4d  31  23  e1  ff  ff  ff  18  68  30  c4  00  00  00  00
      0000060    30  66  29  1a  e1  ff  ff  ff  18  b6  5b  22  e1  ff  ff  ff
      ...
    
      [B] This commit
      # newfs_hammer -L TEST /dev/da2 > /dev/null
      # mount_hammer /dev/da2 /HAMMER
      # hammer volume-add /dev/da3 /HAMMER
      # hammer volume-del /dev/da3 /HAMMER
      # od -tx1 -N 1928 /dev/da3
      0000000    00  00  00  00  00  00  00  00  00  00  00  00  00  00  00  00
      *
      0003600
    
      [C] sizeof ondisk volume header
      # cat ./sizeof.c
      #include <stdio.h>
      #include <vfs/hammer/hammer_disk.h>
      int main(void) {
              printf("%d\n", (int)sizeof(struct hammer_volume_ondisk));
              return 0;
      }
      # gcc -Wall -g ./sizeof.c
      # ./a.out
      1928
    
    (cherry picked from commit bcc535d1f1de62c4c603593151aba54361a6a77c)

Summary of changes:
 sys/vfs/hammer/hammer_volume.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/c34b9df50c3d8107955d628046b82e924e54bac8


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