[PATCH] e2fsprogs : Add stricter checks for blocksize in ext2fs_open

[PATCH] e2fsprogs : Add stricter checks for blocksize in ext2fs_open

[Manish Katiyar]

Below patch adds stricter checks in ext2fs_open() so that we catch bad
block sizes earlier than later.

============================================================================

Signed-off-by: "Manish Katiyar" <mkatiyar@gmail.com>

---
 lib/ext2fs/openfs.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
index fc54afe..670cc7c 100644
--- a/lib/ext2fs/openfs.c
+++ b/lib/ext2fs/openfs.c
@@ -233,7 +233,9 @@ errcode_t ext2fs_open2(const char *name, const
char *io_options,
 	}
 	
 	fs->blocksize = EXT2_BLOCK_SIZE(fs->super);
-	if (fs->blocksize == 0) {
+	if ((fs->blocksize < EXT2_MIN_BLOCK_SIZE) ||
+	    (fs->blocksize > EXT2_MAX_BLOCK_SIZE) ||
+	    (fs->blocksize % EXT2_MIN_BLOCK_SIZE != 0)) {
 		retval = EXT2_ET_CORRUPT_SUPERBLOCK;
 		goto cleanup;
 	}
-- 
1.5.4.3


============================================================================

-- 
Thanks & Regards,
********************************************
Manish Katiyar ( http://mkatiyar.googlepages.com )
3rd Floor, Fair Winds Block
EGL Software Park
Off Intermediate Ring Road
Bangalore 560071, India
***********************************************

Re: [PATCH] e2fsprogs : Add stricter checks for blocksize in ext2fs_open

[Peter Staubach]

Manish Katiyar wrote:
> Below patch adds stricter checks in ext2fs_open() so that we catch bad
> block sizes earlier than later.
>
> ============================================================================
>
> Signed-off-by: "Manish Katiyar" <mkatiyar@gmail.com>
>
> ---
>  lib/ext2fs/openfs.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
>
> diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
> index fc54afe..670cc7c 100644
> --- a/lib/ext2fs/openfs.c
> +++ b/lib/ext2fs/openfs.c
> @@ -233,7 +233,9 @@ errcode_t ext2fs_open2(const char *name, const
> char *io_options,
>  	}
>  	
>  	fs->blocksize = EXT2_BLOCK_SIZE(fs->super);
> -	if (fs->blocksize == 0) {
> +	if ((fs->blocksize < EXT2_MIN_BLOCK_SIZE) ||
> +	    (fs->blocksize > EXT2_MAX_BLOCK_SIZE) ||
> +	    (fs->blocksize % EXT2_MIN_BLOCK_SIZE != 0)) {
>   

It seems to me that this would read more clearly as:

               ((fs->blocksize % EXT2_MIN_BLOCK_SIZE) != 0)) {

    Thanx!

       ps

>  		retval = EXT2_ET_CORRUPT_SUPERBLOCK;
>  		goto cleanup;
>  	}
>   

Re: [PATCH] e2fsprogs : Add stricter checks for blocksize in ext2fs_open

[Theodore Tso]

On Fri, Jul 11, 2008 at 02:19:06PM +0530, Manish Katiyar wrote:
> Below patch adds stricter checks in ext2fs_open() so that we catch bad
> block sizes earlier than later.

That concept seems fine; I'm curious why you found this necessary?
Did you have a corrupted filesystem where this caused major problems?
If so, can I have more details?

>  	fs->blocksize = EXT2_BLOCK_SIZE(fs->super);
> -	if (fs->blocksize == 0) {
> +	if ((fs->blocksize < EXT2_MIN_BLOCK_SIZE) ||
> +	    (fs->blocksize > EXT2_MAX_BLOCK_SIZE) ||
> +	    (fs->blocksize % EXT2_MIN_BLOCK_SIZE != 0)) {

The first and last check is not necessary, given that EXT2_bLOCK_SIZE
is defined as:

#define EXT2_BLOCK_SIZE(s)	 (EXT2_MIN_BLOCK_SIZE << (s)->s_log_block_size)

So by definition, the blocksize will *always* be greater than or equal
to MIN_BLOCK_SIZE, and it always will be a multiple of EXT2_MIN_BLOCK_SIZE.

The more direct check which we could do would be something like this:

	if ((fs->super->s_log_block_size < EXT2_MIN_BLOCK_LOG_SIZE) ||
	    (fs->super->s_log_block_size > EXT2_MAX_BLOCK_LOG_SIZE))
  		retval = EXT2_ET_CORRUPT_SUPERBLOCK;
  		goto cleanup;
  	}

... before setting fs->blocksize.

I'm curious what problem you were worried about that might happen if
fs->blocksize were greater than 64k, though.

							- Ted

Re: [PATCH] e2fsprogs : Add stricter checks for blocksize in ext2fs_open

[Theodore Tso]

This is what I ended up checking into my tree:

From: Manish Katiyar <mkatiyar@gmail.com>
Date: Fri, 11 Jul 2008 17:45:07 -0400
Subject: [PATCH] libext2fs: Add stricter/earlier tests for blocksize in ext2fs_open()

Signed-off-by: "Manish Katiyar" <mkatiyar@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---
 lib/ext2fs/openfs.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
index fc54afe..525693e 100644
--- a/lib/ext2fs/openfs.c
+++ b/lib/ext2fs/openfs.c
@@ -232,11 +232,12 @@ errcode_t ext2fs_open2(const char *name, const char *io_options,
 		}
 	}
 	
-	fs->blocksize = EXT2_BLOCK_SIZE(fs->super);
-	if (fs->blocksize == 0) {
+	if ((fs->super->s_log_block_size + EXT2_MIN_BLOCK_LOG_SIZE) >
+	    EXT2_MAX_BLOCK_LOG_SIZE) {
 		retval = EXT2_ET_CORRUPT_SUPERBLOCK;
 		goto cleanup;
 	}
+	fs->blocksize = EXT2_BLOCK_SIZE(fs->super);
 	if (EXT2_INODE_SIZE(fs->super) < EXT2_GOOD_OLD_INODE_SIZE) {
 		retval = EXT2_ET_CORRUPT_SUPERBLOCK;
 		goto cleanup;
-- 
1.5.6.1.205.ge2c7.dirty