[PATCH] limit minixfs dir_pages on corrupted dir i_size, CVE-2006-6058

[PATCH] limit minixfs dir_pages on corrupted dir i_size, CVE-2006-6058

[Eric Sandeen]

This attempts to address CVE-2006-6058 
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-6058

first reported at http://projects.info-pull.com/mokb/MOKB-17-11-2006.html

Essentially a corrupted minix dir inode reporting a very large
i_size will loop for a very long time in minix_readdir, minix_find_entry,
etc, because on EIO they just move on to try the next page.  This is
under the BKL, printk'ing as well.  This can lock up the machine 
for a very long time.  A simple approach is to at least limit the nr. of 
pages attempted to no more than s_max_size.  (s_max_size is about 256MB for
V1, but 2GB for V2; this could still result in a lot of EIO reads in the V2
case, should the retry loops in minix_readdir & friends be short-circuited
somehow instead?  A simple "break" rather than "continue" on error would 
certainly resolve it, too...)

Signed-off-by: Eric Sandeen <sandeen@redhat.com>

--- linux-2.6.22-rc4.orig/fs/minix/dir.c
+++ linux-2.6.22-rc4/fs/minix/dir.c
@@ -42,7 +42,15 @@ minix_last_byte(struct inode *inode, uns
 
 static inline unsigned long dir_pages(struct inode *inode)
 {
-	return (inode->i_size+PAGE_CACHE_SIZE-1)>>PAGE_CACHE_SHIFT;
+	loff_t size = inode->i_size;
+
+	if (size > minix_sb(inode->i_sb)->s_max_size) {
+		printk("%s: inode %lld i_size > s_max_size\n",
+			__FUNCTION__, inode->i_size);
+		size = minix_sb(inode->i_sb)->s_max_size;
+	}
+
+	return (size+PAGE_CACHE_SIZE-1)>>PAGE_CACHE_SHIFT;
 }
 
 static int dir_commit_chunk(struct page *page, unsigned from, unsigned to)

[PATCH V2] limit minixfs printks on corrupted dir i_size, CVE-2006-6058

[Eric Sandeen]

Perhaps this is simpler, and preferable.  Thanks to adilger for
reminding me about printk_ratelimit.  :)

----

This attempts to address CVE-2006-6058 
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-6058
 
first reported at http://projects.info-pull.com/mokb/MOKB-17-11-2006.html

Essentially a corrupted minix dir inode reporting a very large
i_size will loop for a very long time in minix_readdir, minix_find_entry,
etc, because on EIO they just move on to try the next page.  This is
under the BKL, printk-storming as well.  This can lock up the machine 
for a very long time.  Simply ratelimiting the printks gets things back
under control.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>

Index: linux-2.6.22-rc4/fs/minix/itree_v1.c
===================================================================
--- linux-2.6.22-rc4.orig/fs/minix/itree_v1.c
+++ linux-2.6.22-rc4/fs/minix/itree_v1.c
@@ -27,7 +27,8 @@ static int block_to_path(struct inode * 
 	if (block < 0) {
 		printk("minix_bmap: block<0\n");
 	} else if (block >= (minix_sb(inode->i_sb)->s_max_size/BLOCK_SIZE)) {
-		printk("minix_bmap: block>big\n");
+		if (printk_ratelimit())
+			printk("minix_bmap: block>big\n");
 	} else if (block < 7) {
 		offsets[n++] = block;
 	} else if ((block -= 7) < 512) {
Index: linux-2.6.22-rc4/fs/minix/itree_v2.c
===================================================================
--- linux-2.6.22-rc4.orig/fs/minix/itree_v2.c
+++ linux-2.6.22-rc4/fs/minix/itree_v2.c
@@ -28,7 +28,8 @@ static int block_to_path(struct inode * 
 	if (block < 0) {
 		printk("minix_bmap: block<0\n");
 	} else if (block >= (minix_sb(inode->i_sb)->s_max_size/sb->s_blocksize)) {
-		printk("minix_bmap: block>big\n");
+		if (printk_ratelimit())
+			printk("minix_bmap: block>big\n");
 	} else if (block < 7) {
 		offsets[n++] = block;
 	} else if ((block -= 7) < 256) {

Re: [PATCH V2] limit minixfs printks on corrupted dir i_size, CVE-2006-6058

[Bodo Eggert]

Eric Sandeen <sandeen@sandeen.net> wrote:

> This attempts to address CVE-2006-6058
> http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-6058
>  
> first reported at http://projects.info-pull.com/mokb/MOKB-17-11-2006.html
> 
> Essentially a corrupted minix dir inode reporting a very large
> i_size will loop for a very long time in minix_readdir, minix_find_entry,
> etc, because on EIO they just move on to try the next page.  This is
> under the BKL, printk-storming as well.  This can lock up the machine
> for a very long time.  Simply ratelimiting the printks gets things back
> under control.

> Index: linux-2.6.22-rc4/fs/minix/itree_v1.c
> ===================================================================
> --- linux-2.6.22-rc4.orig/fs/minix/itree_v1.c
> +++ linux-2.6.22-rc4/fs/minix/itree_v1.c
> @@ -27,7 +27,8 @@ static int block_to_path(struct inode *
>  if (block < 0) {
>  printk("minix_bmap: block<0\n");
>  } else if (block >= (minix_sb(inode->i_sb)->s_max_size/BLOCK_SIZE)) {
> -             printk("minix_bmap: block>big\n");
> +             if (printk_ratelimit())
> +                     printk("minix_bmap: block>big\n");

Warning: I'm only looking at the patch.

You are supposed to print an error message for a user, not to write in a
chat window to a 1337 script kiddie. OK, you just matched the current style,
and your patch is IMHO OK for a quick security fix, but:

- Security fixes should be CCed to the security mailing list, shouldn't they?
  (It might be security@ or stable@, I'll remember tomorrow, but then I'd
   forget to comment)
- Imagine you have three mounts containing a minix fs, how can you tell which
  one is the the defective one?
- The message says "minix_bmap", while the patch suggests it's in
  block_to_path. Therefore I asume "minix_bmap" to have only random
  informational value.
- Does block < 0 or block > $size make a difference?
- the printk lacks the loglevel.
- Asuming minix supports error handling, shouldn't it do something?

I'd suggest a message saying something like "minix: Bad block address on
device 08:15, needs fsck".
-- 
Oops. My brain just hit a bad sector. 

Friß, Spammer: ei@lyUAkvOE.7eggert.dyndns.org wod@2lvjUzk.7eggert.dyndns.org
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Re: [PATCH V2] limit minixfs printks on corrupted dir i_size, CVE-2006-6058

[Eric Sandeen]

Bodo Eggert wrote:

> Warning: I'm only looking at the patch.
> 
> You are supposed to print an error message for a user, not to write in a
> chat window to a 1337 script kiddie. OK, you just matched the current style,
> and your patch is IMHO OK for a quick security fix, but:
> 
> - Security fixes should be CCed to the security mailing list, shouldn't they?
>   (It might be security@ or stable@, I'll remember tomorrow, but then I'd
>    forget to comment)

ok.

> - Imagine you have three mounts containing a minix fs, how can you tell which
>   one is the the defective one?

good point.

> - The message says "minix_bmap", while the patch suggests it's in
>   block_to_path. Therefore I asume "minix_bmap" to have only random
>   informational value.

Yup, you're right.

> - Does block < 0 or block > $size make a difference?

well, block > size is likely to arrive from a corrupt i_size, and the
insistence upon going ahead and checking the next page after
encountering an error on the last one... I don't have any scenario in
mind where we'd be repeatedly trying to check blocks < 0.

> - the printk lacks the loglevel.

As do all other printk's in minixfs... (hm and 11,619 other printk's in
the kernel :) )

> - Asuming minix supports error handling, shouldn't it do something?
> 
> I'd suggest a message saying something like "minix: Bad block address on
> device 08:15, needs fsck".

Fair enough, as you said I was just fixing up the issue, not rewriting
the code around it.  But yes, I should probably have considered at least
a better message here.  I can fix this up & resend.  But I'm not
promising to audit all other printk's in minixfs this time around.  ;-)

-Eric