Should exportfs/mountd cope with case-insensitive directory names.

[NeilBrown <neilb@suse.de>]

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Hi,
 I came across an interesting issue recently.

Suppose you have a filesystem which supports case-insensitive file names
(like VFAT, but in this particular case 'NSS' - Novell Storage Services).

And support you export some subdirectory (or sub-volume) using a
non-canonical name.
i.e. you "mkdir /path/export", the put "/path/EXPORT" in /etc/exports and
mount  server:/path/EXPORT from some client.

This all works until the export cache times out and the kernel asks mountd
if "/path/export" is exported.  mountd says "no" and suddenly all accesses
fail.

I don't think much of case-insensitive file names, but I suspect we should
either make this work, it issue a warning as to why it is failing.
A simple work around is to export the canonical name and use it when
mounting.  But if the sysadmin doesn't know they need to, they are unlikely
to guess.

I don't think there is any API to test if a name is canonical, or to get the
canonical name, so I cannot see any way in advance to see if this problem
situation has arisen.  So the only option I can think of is to fix it.

The following patch (or something much like it for an older nfs-utils) seems
to do the trick.

What do people think?  Is this a reasonable thing to do?  Is it likely to
have negative consequences that I haven't thought of?

Thanks,
NeilBrown



diff --git a/utils/mountd/cache.c b/utils/mountd/cache.c
index 9a1bb2767ac2..2d91db76b867 100644
--- a/utils/mountd/cache.c
+++ b/utils/mountd/cache.c
@@ -377,6 +377,28 @@ static char *next_mnt(void **v, char *p)
 	return me->mnt_dir;
 }
 
+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 (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 +409,7 @@ 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 +418,7 @@ 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));
 }

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