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, 3 insertions, 0 deletions

diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h
index f44f71b..5007f78 100644
--- a/fs/ecryptfs/ecryptfs_kernel.h
+++ b/fs/ecryptfs/ecryptfs_kernel.h
@@ -323,6 +323,8 @@ struct ecryptfs_key_tfm {
 	unsigned char cipher_name[ECRYPTFS_MAX_CIPHER_NAME_SIZE + 1];
 };
 
+extern struct mutex key_tfm_list_mutex;
+
 /**
  * This struct is to enable a mount-wide passphrase/salt combo. This
  * is more or less a stopgap to provide similar functionality to other
@@ -617,6 +619,7 @@ ecryptfs_add_new_key_tfm(struct ecryptfs_key_tfm **key_tfm, char *cipher_name,
 			 size_t key_size);
 int ecryptfs_init_crypto(void);
 int ecryptfs_destroy_crypto(void);
+int ecryptfs_tfm_exists(char *cipher_name, struct ecryptfs_key_tfm **key_tfm);
 int ecryptfs_get_tfm_and_mutex_for_cipher_name(struct crypto_blkcipher **tfm,
 					       struct mutex **tfm_mutex,
 					       char *cipher_name);