Re: [nfs-utils PATCH] mountd: fix is_subdirectory to understand '/'

["J. Bruce Fields" <bfields@fieldses.org>]

On Thu, Dec 13, 2012 at 11:23:42AM +1100, NeilBrown wrote:
> 
> The is_subdirectory() function checks if a given 'child' is a subdirectory
> of the given 'parent'.
> However it always fails if 'parent' == "/"  (because 'child' doesn't begin
> with 'parent' followed by "/").
> 
> So change is_subdirectory() to special-case "/".

Might be slightly more elegant to deal with this as a case of a parent
directory with a terminating "/" rather than as a special case, and that
might make this a little more robust.  E.g.:

	size_t l = strlen(parent);

	while (l && parent[l-1] == '/')
		l--;
	return (l <= strlen(child))
		&& strncmp(parent, child, l) == 0
		&& (child[l] == '/' || child[l] == '\0');

?

--b.

> 
> subexport() also tests if one directory is a subdirectory of the
> other, and contains the same bug.  So change it to use is_subdirectory().
> 
> Finally, move is_subdirectory() and related path_matches() and
> export_matches() earlier in the file to avoid a forward-reference.
> 
> This patch fixes a bug wherein if you export "/" with 'crossmnt', the
> crossmnt flag is ineffective and you can only access the root
> filesystem, not any descendants.
> 
> Signed-off-by: NeilBrown <neilb@suse.de>
> 
> diff --git a/utils/mountd/cache.c b/utils/mountd/cache.c
> index 3853bb6..45012be 100644
> --- a/utils/mountd/cache.c
> +++ b/utils/mountd/cache.c
> @@ -343,6 +343,30 @@ static char *next_mnt(void **v, char *p)
>  	return me->mnt_dir;
>  }
>  
> +static int is_subdirectory(char *child, char *parent)
> +{
> +	size_t l = strlen(parent);
> +
> +	if (strcmp(parent, "/") == 0)
> +		return 1;
> +
> +	return strcmp(child, parent) == 0
> +		|| (strncmp(child, parent, l) == 0 && child[l] == '/');
> +}
> +
> +static int path_matches(nfs_export *exp, char *path)
> +{
> +	if (exp->m_export.e_flags & NFSEXP_CROSSMOUNT)
> +		return is_subdirectory(path, exp->m_export.e_path);
> +	return strcmp(path, exp->m_export.e_path) == 0;
> +}
> +
> +static int
> +export_matches(nfs_export *exp, char *dom, char *path, struct addrinfo *ai)
> +{
> +	return path_matches(exp, path) && client_matches(exp, dom, ai);
> +}
> +
>  /* True iff e1 is a child of e2 and e2 has crossmnt set: */
>  static bool subexport(struct exportent *e1, struct exportent *e2)
>  {
> @@ -350,8 +374,7 @@ static bool subexport(struct exportent *e1, struct exportent *e2)
>  	size_t l2 = strlen(p2);
>  
>  	return e2->e_flags & NFSEXP_CROSSMOUNT
> -	       && strncmp(p1, p2, l2) == 0
> -	       && p1[l2] == '/';
> +		&& is_subdirectory(p1, p2);
>  }
>  
>  struct parsed_fsid {
> @@ -752,27 +775,6 @@ static int dump_to_cache(FILE *f, char *domain, char *path, struct exportent *ex
>  	return qword_eol(f);
>  }
>  
> -static int is_subdirectory(char *child, char *parent)
> -{
> -	size_t l = strlen(parent);
> -
> -	return strcmp(child, parent) == 0
> -		|| (strncmp(child, parent, l) == 0 && child[l] == '/');
> -}
> -
> -static int path_matches(nfs_export *exp, char *path)
> -{
> -	if (exp->m_export.e_flags & NFSEXP_CROSSMOUNT)
> -		return is_subdirectory(path, exp->m_export.e_path);
> -	return strcmp(path, exp->m_export.e_path) == 0;
> -}
> -
> -static int
> -export_matches(nfs_export *exp, char *dom, char *path, struct addrinfo *ai)
> -{
> -	return path_matches(exp, path) && client_matches(exp, dom, ai);
> -}
> -
>  static nfs_export *
>  lookup_export(char *dom, char *path, struct addrinfo *ai)
>  {