[PATCH] xfs_repair: do not check symlink component lengths

[PATCH] xfs_repair: do not check symlink component lengths

[Eric Sandeen]

As reported by Andy Grimm,

# ln -s $( python -c 'print "a" * 260' ) /mnt/foo

will succeed on xfs, but then xfs_repair will complain:

component of symlink in inode 131 too long
problem with symbolic link in inode 131
would have cleared inode 131

The kernel checks the total length of the symlink on both read
and write, but does not look at component paths.

Looking around the kernel, no other filesystem checks component
lengths, nor does the vfs.  And as Andy points out, the target
could even be on a different filesystem, with different limitations.

And having a "too-long" component doesn't even seem like something
likely to stem from disk corruption anyway, so I'm not sure why repair
should care.

Therefore I propose removing the component length checks from xfs_repair.

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

diff --git a/repair/dinode.c b/repair/dinode.c
index 38a6562..73e4b9e 100644
--- a/repair/dinode.c
+++ b/repair/dinode.c
@@ -1333,7 +1333,7 @@ process_symlink(
 	xfs_dinode_t	*dino,
 	blkmap_t 	*blkmap)
 {
-	char			*symlink, *cptr;
+	char			*symlink;
 	char			data[MAXPATHLEN];
 
 	/*
@@ -1380,31 +1380,6 @@ _("found illegal null character in symlink inode %" PRIu64 "\n"),
 		return(1);
 	}
 
-	/*
-	 * check for any component being too long
-	 */
-	if (be64_to_cpu(dino->di_size) >= MAXNAMELEN)  {
-		cptr = strchr(symlink, '/');
-
-		while (cptr != NULL)  {
-			if (cptr - symlink >= MAXNAMELEN)  {
-				do_warn(
-_("component of symlink in inode %" PRIu64 " too long\n"),
-					lino);
-				return(1);
-			}
-			symlink = cptr + 1;
-			cptr = strchr(symlink, '/');
-		}
-
-		if (strlen(symlink) >= MAXNAMELEN)  {
-			do_warn(
-_("component of symlink in inode %" PRIu64 " too long\n"),
-				lino);
-			return(1);
-		}
-	}
-
 	return(0);
 }
 

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Re: [PATCH] xfs_repair: do not check symlink component lengths

[Brian Foster]

On Fri, Dec 05, 2014 at 02:30:14PM -0600, Eric Sandeen wrote:
> As reported by Andy Grimm,
> 
> # ln -s $( python -c 'print "a" * 260' ) /mnt/foo
> 
> will succeed on xfs, but then xfs_repair will complain:
> 
> component of symlink in inode 131 too long
> problem with symbolic link in inode 131
> would have cleared inode 131
> 
> The kernel checks the total length of the symlink on both read
> and write, but does not look at component paths.
> 
> Looking around the kernel, no other filesystem checks component
> lengths, nor does the vfs.  And as Andy points out, the target
> could even be on a different filesystem, with different limitations.
> 

Interesting, but we do enforce dentry name limits, yes? At least, I
can't create such a component on an XFS fs (haven't dug into where that
is enforced).

> And having a "too-long" component doesn't even seem like something
> likely to stem from disk corruption anyway, so I'm not sure why repair
> should care.
> 

My guess would be the intent is based on the above, where we can't
create such a long component name and thus a component that exceeds the
limits must be "invalid."

That said, a broken symlink is generally valid and not the same as
corruption, so I think I agree that this is somewhat misplaced
functionality...

> Therefore I propose removing the component length checks from xfs_repair.
> 
> Andy Grimm <agrimm@redhat.com>
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

> 
> diff --git a/repair/dinode.c b/repair/dinode.c
> index 38a6562..73e4b9e 100644
> --- a/repair/dinode.c
> +++ b/repair/dinode.c
> @@ -1333,7 +1333,7 @@ process_symlink(
>  	xfs_dinode_t	*dino,
>  	blkmap_t 	*blkmap)
>  {
> -	char			*symlink, *cptr;
> +	char			*symlink;
>  	char			data[MAXPATHLEN];
>  
>  	/*
> @@ -1380,31 +1380,6 @@ _("found illegal null character in symlink inode %" PRIu64 "\n"),
>  		return(1);
>  	}
>  
> -	/*
> -	 * check for any component being too long
> -	 */
> -	if (be64_to_cpu(dino->di_size) >= MAXNAMELEN)  {
> -		cptr = strchr(symlink, '/');
> -
> -		while (cptr != NULL)  {
> -			if (cptr - symlink >= MAXNAMELEN)  {
> -				do_warn(
> -_("component of symlink in inode %" PRIu64 " too long\n"),
> -					lino);
> -				return(1);
> -			}
> -			symlink = cptr + 1;
> -			cptr = strchr(symlink, '/');
> -		}
> -
> -		if (strlen(symlink) >= MAXNAMELEN)  {
> -			do_warn(
> -_("component of symlink in inode %" PRIu64 " too long\n"),
> -				lino);
> -			return(1);
> -		}
> -	}
> -
>  	return(0);
>  }
>  
> 
> _______________________________________________
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