efivarfs: guid part of filenames are case-insensitive

It makes no sense to treat the following filenames as unique,

	VarName-abcdefab-abcd-abcd-abcd-abcdefabcdef
	VarName-ABCDEFAB-ABCD-ABCD-ABCD-ABCDEFABCDEF
	VarName-ABcDEfAB-ABcD-ABcD-ABcD-ABcDEfABcDEf
	VarName-aBcDEfAB-aBcD-aBcD-aBcD-aBcDEfaBcDEf
	... etc ...

since the guid will be converted into a binary representation, which
has no case.

Roll our own dentry operations so that we can treat the variable name
part of filenames ("VarName" in the above example) as case-sensitive,
but the guid portion as case-insensitive. That way, efivarfs will
refuse to create the above files if any one already exists.

Reported-by: Lingzhu Xiang <lxiang@redhat.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Jeremy Kerr <jeremy.kerr@canonical.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

1 files changed, 93 insertions, 2 deletions

diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index 868cea5cd4b8..8bcb5958f21a 100644
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -1043,6 +1043,84 @@ static int efivarfs_unlink(struct inode *dir, struct dentry *dentry)
         return -EINVAL;
 };
 
+/*
+ * Compare two efivarfs file names.
+ *
+ * An efivarfs filename is composed of two parts,
+ *
+ *      1. A case-sensitive variable name
+ *      2. A case-insensitive GUID
+ *
+ * So we need to perform a case-sensitive match on part 1 and a
+ * case-insensitive match on part 2.
+ */
+static int efivarfs_d_compare(const struct dentry *parent, const struct inode *pinode,
+                              const struct dentry *dentry, const struct inode *inode,
+                              unsigned int len, const char *str,
+                              const struct qstr *name)
+{
+        int guid = len - GUID_LEN;
+
+        if (name->len != len)
+                return 1;
+
+        /* Case-sensitive compare for the variable name */
+        if (memcmp(str, name->name, guid))
+                return 1;
+
+        /* Case-insensitive compare for the GUID */
+        return strncasecmp(name->name + guid, str + guid, GUID_LEN);
+}
+
+static int efivarfs_d_hash(const struct dentry *dentry,
+                           const struct inode *inode, struct qstr *qstr)
+{
+        unsigned long hash = init_name_hash();
+        const unsigned char *s = qstr->name;
+        unsigned int len = qstr->len;
+
+        if (!efivarfs_valid_name(s, len))
+                return -EINVAL;
+
+        while (len-- > GUID_LEN)
+                hash = partial_name_hash(*s++, hash);
+
+        /* GUID is case-insensitive. */
+        while (len--)
+                hash = partial_name_hash(tolower(*s++), hash);
+
+        qstr->hash = end_name_hash(hash);
+        return 0;
+}
+
+/*
+ * Retaining negative dentries for an in-memory filesystem just wastes
+ * memory and lookup time: arrange for them to be deleted immediately.
+ */
+static int efivarfs_delete_dentry(const struct dentry *dentry)
+{
+        return 1;
+}
+
+static struct dentry_operations efivarfs_d_ops = {
+        .d_compare = efivarfs_d_compare,
+        .d_hash = efivarfs_d_hash,
+        .d_delete = efivarfs_delete_dentry,
+};
+
+static struct dentry *efivarfs_alloc_dentry(struct dentry *parent, char *name)
+{
+        struct qstr q;
+
+        q.name = name;
+        q.len = strlen(name);
+
+        if (efivarfs_d_hash(NULL, NULL, &q))
+                return NULL;
+
+        return d_alloc(parent, &q);
+}
+
 static int efivarfs_fill_super(struct super_block *sb, void *data, int silent)
 {
         struct inode *inode = NULL;
@@ -1058,6 +1136,7 @@ static int efivarfs_fill_super(struct super_block *sb, void *data, int silent)
         sb->s_blocksize_bits    = PAGE_CACHE_SHIFT;
         sb->s_magic             = EFIVARFS_MAGIC;
         sb->s_op                = &efivarfs_ops;
+        sb->s_d_op              = &efivarfs_d_ops;
         sb->s_time_gran         = 1;
 
         inode = efivarfs_get_inode(sb, NULL, S_IFDIR | 0755, 0);
@@ -1098,7 +1177,7 @@ static int efivarfs_fill_super(struct super_block *sb, void *data, int silent)
                 if (!inode)
                         goto fail_name;
 
-                dentry = d_alloc_name(root, name);
+                dentry = efivarfs_alloc_dentry(root, name);
                 if (!dentry)
                         goto fail_inode;
 
@@ -1148,8 +1227,20 @@ static struct file_system_type efivarfs_type = {
         .kill_sb = efivarfs_kill_sb,
 };
 
+/*
+ * Handle negative dentry.
+ */
+static struct dentry *efivarfs_lookup(struct inode *dir, struct dentry *dentry,
+                                      unsigned int flags)
+{
+        if (dentry->d_name.len > NAME_MAX)
+                return ERR_PTR(-ENAMETOOLONG);
+        d_add(dentry, NULL);
+        return NULL;
+}
+
 static const struct inode_operations efivarfs_dir_inode_operations = {
-        .lookup = simple_lookup,
+        .lookup = efivarfs_lookup,
         .unlink = efivarfs_unlink,
         .create = efivarfs_create,
 };