mountd: add support for case-insensitive file names

Case insensitive filesystems support textually distinct names for the
same directory. i.e. you can access it with a name other than the
canonical name.
For example if you
  mkdir /mnt/export

then add /mnt/EXPORT to /etc/exports, and on a client
  mount server:/mnt/EXPORT /import

then the mount will work, but if the kernel on the server needs to
refresh the export information, it will ask about "/mnt/export", which
is not listed in /etc/exports and so will fail.

To fix this we need mountd to perform case-insensitive name
comparisons, but only when the filesystem would, and in exactly the
same way that the filesystem would.

So, when comparing paths for equality first try some simple heuristics
which will not be fooled by case and then ask the kernel if they are
the same.

By preference we use name_to_handle_at() as it reports the mntid which
can distinguish between bind mounts.  If that is not available, use
lstat() and compare rdev and ino.

Acked-by: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Steve Dickson <steved@redhat.com>

2 files changed, 83 insertions, 3 deletions

diff --git a/configure.ac b/configure.ac
index 7b93de6..408f4c8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -411,7 +411,7 @@ AC_CHECK_FUNCS([alarm atexit dup2 fdatasync ftruncate getcwd \
                getnameinfo getrpcbyname getifaddrs \
                gettimeofday hasmntopt inet_ntoa innetgr memset mkdir pathconf \
                ppoll realpath rmdir select socket strcasecmp strchr strdup \
-               strerror strrchr strtol strtoul sigprocmask])
+               strerror strrchr strtol strtoul sigprocmask name_to_handle_at])
 
 
 dnl *************************************************************
diff --git a/utils/mountd/cache.c b/utils/mountd/cache.c
index 9a1bb27..b0cc6a8 100644
--- a/utils/mountd/cache.c
+++ b/utils/mountd/cache.c
@@ -377,6 +377,86 @@ static char *next_mnt(void **v, char *p)
 	return me->mnt_dir;
 }
 
+/* same_path() check is two paths refer to the same directory.
+ * We don't rely on 'strcmp()' as some filesystems support case-insensitive
+ * names and we might have two different names for the one directory.
+ * Theoretically the lengths of the names could be different, but the
+ * number of components must be the same.
+ * So if the paths have the same number of components (but aren't identical)
+ * we ask the kernel if they are the same thing.
+ * By preference we use name_to_handle_at(), as the mntid it returns
+ * will distinguish between bind-mount points.  If that isn't available
+ * we fall back on lstat, which is usually good enough.
+ */
+static inline int count_slashes(char *p)
+{
+	int cnt = 0;
+	while (*p)
+		if (*p++ == '/')
+			cnt++;
+	return cnt;
+}
+
+static int same_path(char *child, char *parent, int len)
+{
+	static char p[PATH_MAX];
+	struct stat sc, sp;
+
+	if (len <= 0)
+		len = strlen(child);
+	strncpy(p, child, len);
+	p[len] = 0;
+	if (strcmp(p, parent) == 0)
+		return 1;
+
+	/* If number of '/' are different, they must be different */
+	if (count_slashes(p) != count_slashes(parent))
+		return 0;
+
+#if HAVE_NAME_TO_HANDLE_AT
+	struct {
+		struct file_handle fh;
+		unsigned char handle[128];
+	} fchild, fparent;
+	int mnt_child, mnt_parent;
+
+	fchild.fh.handle_bytes = 128;
+	fparent.fh.handle_bytes = 128;
+	if (name_to_handle_at(AT_FDCWD, p, &fchild.fh, &mnt_child, 0) != 0) {
+		if (errno == ENOSYS)
+			goto fallback;
+		return 0;
+	}
+	if (name_to_handle_at(AT_FDCWD, parent, &fparent.fh, &mnt_parent, 0) != 0)
+		return 0;
+
+	if (mnt_child != mnt_parent ||
+	    fchild.fh.handle_bytes != fparent.fh.handle_bytes ||
+	    fchild.fh.handle_type != fparent.fh.handle_type ||
+	    memcmp(fchild.handle, fparent.handle,
+		   fchild.fh.handle_bytes) != 0)
+		return 0;
+
+	return 1;
+fallback:
+#endif
+
+	/* This is nearly good enough.  However if a directory is
+	 * bind-mounted in two places and both are exported, it
+	 * could give a false positive
+	 */
+	if (lstat(p, &sc) != 0)
+		return 0;
+	if (lstat(parent, &sp) != 0)
+		return 0;
+	if (sc.st_dev != sp.st_dev)
+		return 0;
+	if (sc.st_ino != sp.st_ino)
+		return 0;
+
+	return 1;
+}
+
 static int is_subdirectory(char *child, char *parent)
 {
 	/* Check is child is strictly a subdirectory of
@@ -387,7 +467,7 @@ static int is_subdirectory(char *child, char *parent)
 	if (strcmp(parent, "/") == 0 && child[1] != 0)
 		return 1;
 
-	return (strncmp(child, parent, l) == 0 && child[l] == '/');
+	return (same_path(child, parent, l) && child[l] == '/');
 }
 
 static int path_matches(nfs_export *exp, char *path)
@@ -396,7 +476,7 @@ static int path_matches(nfs_export *exp, char *path)
 	 * exact match, or does the export have CROSSMOUNT, and path
 	 * is a descendant?
 	 */
-	return strcmp(path, exp->m_export.e_path) == 0
+	return same_path(path, exp->m_export.e_path, 0)
 		|| ((exp->m_export.e_flags & NFSEXP_CROSSMOUNT)
 		    && is_subdirectory(path, exp->m_export.e_path));
 }