Re: [PATCH] isofs: mounting to regular file may succeed

[Kirill Kuvaldin]

On Sat, Jul 14, 2007 at 09:16:51PM +0200, Jan Engelhardt wrote:
 
 On Jul 14 2007 03:47, Kirill Kuvaldin wrote:
 
 We then can mount it to a regular file:
 
 Wow, this is news to me. Since when is it possible to mount files to files?
 

It is possible to mount a regular file to another one with --bind.
The problem in question is that mounting a malformed ISO 9660 image to a
directory fails, but to a regular file - succeeds.

Kirill
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Re: [PATCH] isofs: mounting to regular file may succeed

[Kirill Kuvaldin]

On Sat, Jul 14, 2007 at 03:47:21AM +0400, Kirill Kuvaldin wrote:
 $ dd if=correct.iso of=bad.iso bs=4k count=8

Oops, sorry, the right command should be:

dd if=correct.iso of=bad.iso bs=4k seek=8
   
 

Kirill
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[PATCH] isofs: mounting to regular file may succeed

[Kirill Kuvaldin]

It turned out that mounting a corrupted ISO image to a regular file may
succeed, e.g. if an image was prepared as follows:

$ dd if=correct.iso of=bad.iso bs=4k count=8

We then can mount it to a regular file:

# mount -o loop -t iso9660 bad.iso /tmp/file

But mounting it to a directory fails with -ENOTDIR, simply because 
the root directory inode doesn't have S_IFDIR set and the condition
in graft_tree() is met:

if (S_ISDIR(nd-dentry-d_inode-i_mode) !=
  S_ISDIR(mnt-mnt_root-d_inode-i_mode))
return -ENOTDIR

This is because the root directory inode was read from an incorrect
block. It's supposed to be read from sbi-s_firstdatazone, which is
an absolute value and gets messed up in the case of an incorrect image.

In order to somehow circumvent this we have to check that the root
directory inode is actually a directory after all.


Signed-off-by: Kirill Kuvaldin [EMAIL PROTECTED]

diff --git a/fs/isofs/inode.c b/fs/isofs/inode.c
index 5c3eecf..ce5062a 100644
--- a/fs/isofs/inode.c
+++ b/fs/isofs/inode.c
@@ -840,6 +840,15 @@ root_found:
goto out_no_root;
if (!inode-i_op)
goto out_bad_root;
+
+   /* Make sure the root inode is a directory */
+   if (!S_ISDIR(inode-i_mode)) {
+   printk(KERN_WARNING
+   isofs_fill_super: root inode is not a directory. 
+   Corrupted media?\n);
+   goto out_iput;
+   }
+
/* get the root dentry */
s-s_root = d_alloc_root(inode);
if (!(s-s_root))
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