ecryptfs: check for existing key_tfm at mount time

Jeff Moyer pointed out that a mount; umount loop of ecryptfs, with the same
cipher & other mount options, created a new ecryptfs_key_tfm_cache item
each time, and the cache could grow quite large this way.

Looking at this with mhalcrow, we saw that ecryptfs_parse_options()
unconditionally called ecryptfs_add_new_key_tfm(), which is what was adding
these items.

Refactor ecryptfs_get_tfm_and_mutex_for_cipher_name() to create a new
helper function, ecryptfs_tfm_exists(), which checks for the cipher on the
cached key_tfm_list, and sets a pointer to it if it exists.  This can then
be called from ecryptfs_parse_options(), and new key_tfm's can be added
only when a cached one is not found.

With list locking changes suggested by akpm.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Cc: Michael Halcrow <mhalcrow@us.ibm.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
index dc620fc16595..778c420e4cac 100644
--- a/fs/ecryptfs/main.c
+++ b/fs/ecryptfs/main.c
@@ -410,9 +410,13 @@ static int ecryptfs_parse_options(struct super_block *sb, char *options)
         if (!cipher_key_bytes_set) {
                 mount_crypt_stat->global_default_cipher_key_size = 0;
         }
-        rc = ecryptfs_add_new_key_tfm(
-                NULL, mount_crypt_stat->global_default_cipher_name,
-                mount_crypt_stat->global_default_cipher_key_size);
+        mutex_lock(&key_tfm_list_mutex);
+        if (!ecryptfs_tfm_exists(mount_crypt_stat->global_default_cipher_name,
+                                 NULL))
+                rc = ecryptfs_add_new_key_tfm(
+                        NULL, mount_crypt_stat->global_default_cipher_name,
+                        mount_crypt_stat->global_default_cipher_key_size);
+        mutex_unlock(&key_tfm_list_mutex);
         if (rc) {
                 printk(KERN_ERR "Error attempting to initialize cipher with "
                        "name = [%s] and key size = [%td]; rc = [%d]\n",