On 12/19/2011 04:31 PM, Tyler Hicks wrote: > statfs() calls on eCryptfs files returned the wrong filesystem type and, > when using filename encryption, the wrong maximum filename length. > > If mount-wide filename encryption is enabled, the cipher block size and > the lower filesystem's max filename length will determine the max > eCryptfs filename length. Pre-tested, known good lengths are used when > the lower filesystem's namelen is 255 and a cipher with 8 or 16 byte > block sizes is used. In other, less common cases, we fall back to a safe > rounded-down estimate when determining the eCryptfs namelen. > > https://launchpad.net/bugs/885744 > > Signed-off-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxx> > Reported-by: Kees Cook <keescook@xxxxxxxxxxxx> So this looks good Reviewed-by: John Johansen <john.johansen@xxxxxxxxxxxxx> > --- > Changes from v1: > - provide more clarity in the commit message > - unify code paths for setting namelen when lower_namelen == NAME_MAX and > cipher block size is 8 or 16 bytes > - change ecryptfs_set_f_namelen() parameter types from size_t to long, to > match the type of struct kstatfs.f_namelen > - check if (*namelen) is less than zero after going through the estimation > algorithm and, if so, set it to 0 > > fs/ecryptfs/crypto.c | 68 ++++++++++++++++++++++++++++++++++++---- > fs/ecryptfs/ecryptfs_kernel.h | 5 +++ > fs/ecryptfs/keystore.c | 9 ++--- > fs/ecryptfs/super.c | 14 ++++++++- > 4 files changed, 82 insertions(+), 14 deletions(-) > > diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c > index 2a83425..d3c8776 100644 > --- a/fs/ecryptfs/crypto.c > +++ b/fs/ecryptfs/crypto.c > @@ -2026,6 +2026,17 @@ out: > return; > } > > +static size_t ecryptfs_max_decoded_size(size_t encoded_size) > +{ > + /* Not exact; conservatively long. Every block of 4 > + * encoded characters decodes into a block of 3 > + * decoded characters. This segment of code provides > + * the caller with the maximum amount of allocated > + * space that @dst will need to point to in a > + * subsequent call. */ > + return ((encoded_size + 1) * 3) / 4; > +} > + > /** > * ecryptfs_decode_from_filename > * @dst: If NULL, this function only sets @dst_size and returns. If > @@ -2044,13 +2055,7 @@ ecryptfs_decode_from_filename(unsigned char *dst, size_t *dst_size, > size_t dst_byte_offset = 0; > > if (dst == NULL) { > - /* Not exact; conservatively long. Every block of 4 > - * encoded characters decodes into a block of 3 > - * decoded characters. This segment of code provides > - * the caller with the maximum amount of allocated > - * space that @dst will need to point to in a > - * subsequent call. */ > - (*dst_size) = (((src_size + 1) * 3) / 4); > + (*dst_size) = ecryptfs_max_decoded_size(src_size); > goto out; > } > while (src_byte_offset < src_size) { > @@ -2275,3 +2280,52 @@ out_free: > out: > return rc; > } > + > +#define ENC_NAME_MAX_BLOCKLEN_8_OR_16 143 > + > +int ecryptfs_set_f_namelen(long *namelen, long lower_namelen, > + struct ecryptfs_mount_crypt_stat *mount_crypt_stat) > +{ > + struct blkcipher_desc desc; > + struct mutex *tfm_mutex; > + size_t cipher_blocksize; > + int rc; > + > + if (!(mount_crypt_stat->flags & ECRYPTFS_GLOBAL_ENCRYPT_FILENAMES)) { > + (*namelen) = lower_namelen; > + return 0; > + } > + > + rc = ecryptfs_get_tfm_and_mutex_for_cipher_name(&desc.tfm, &tfm_mutex, > + mount_crypt_stat->global_default_fn_cipher_name); > + if (unlikely(rc)) { > + (*namelen) = 0; > + return rc; > + } > + > + mutex_lock(tfm_mutex); > + cipher_blocksize = crypto_blkcipher_blocksize(desc.tfm); > + mutex_unlock(tfm_mutex); > + > + /* Return an exact amount for the common cases */ > + if (lower_namelen == NAME_MAX > + && (cipher_blocksize == 8 || cipher_blocksize == 16)) { > + (*namelen) = ENC_NAME_MAX_BLOCKLEN_8_OR_16; > + return 0; > + } > + > + /* Return a safe estimate for the uncommon cases */ > + (*namelen) = lower_namelen; > + (*namelen) -= ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX_SIZE; > + /* Since this is the max decoded size, subtract 1 "decoded block" len */ > + (*namelen) = ecryptfs_max_decoded_size(*namelen) - 3; > + (*namelen) -= ECRYPTFS_TAG_70_MAX_METADATA_SIZE; > + (*namelen) -= ECRYPTFS_FILENAME_MIN_RANDOM_PREPEND_BYTES; > + /* Worst case is that the filename is padded nearly a full block size */ > + (*namelen) -= cipher_blocksize - 1; > + > + if ((*namelen) < 0) > + (*namelen) = 0; > + > + return 0; > +} > diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h > index a9f29b1..7cad6b0 100644 > --- a/fs/ecryptfs/ecryptfs_kernel.h > +++ b/fs/ecryptfs/ecryptfs_kernel.h > @@ -157,6 +157,9 @@ ecryptfs_get_key_payload_data(struct key *key) > #define ECRYPTFS_NON_NULL 0x42 /* A reasonable substitute for NULL */ > #define MD5_DIGEST_SIZE 16 > #define ECRYPTFS_TAG_70_DIGEST_SIZE MD5_DIGEST_SIZE > +#define ECRYPTFS_TAG_70_MIN_METADATA_SIZE (1 + 1 + ECRYPTFS_SIG_SIZE + 1 + 1) > +#define ECRYPTFS_TAG_70_MAX_METADATA_SIZE (ECRYPTFS_TAG_70_MIN_METADATA_SIZE \ > + + 1) > #define ECRYPTFS_FEK_ENCRYPTED_FILENAME_PREFIX "ECRYPTFS_FEK_ENCRYPTED." > #define ECRYPTFS_FEK_ENCRYPTED_FILENAME_PREFIX_SIZE 23 > #define ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX "ECRYPTFS_FNEK_ENCRYPTED." > @@ -696,6 +699,8 @@ ecryptfs_parse_tag_70_packet(char **filename, size_t *filename_size, > size_t *packet_size, > struct ecryptfs_mount_crypt_stat *mount_crypt_stat, > char *data, size_t max_packet_size); > +int ecryptfs_set_f_namelen(long *namelen, long lower_namelen, > + struct ecryptfs_mount_crypt_stat *mount_crypt_stat); > int ecryptfs_derive_iv(char *iv, struct ecryptfs_crypt_stat *crypt_stat, > loff_t offset); > > diff --git a/fs/ecryptfs/keystore.c b/fs/ecryptfs/keystore.c > index ac1ad48..06aab59 100644 > --- a/fs/ecryptfs/keystore.c > +++ b/fs/ecryptfs/keystore.c > @@ -678,10 +678,7 @@ ecryptfs_write_tag_70_packet(char *dest, size_t *remaining_bytes, > * Octets N3-N4: Block-aligned encrypted filename > * - Consists of a minimum number of random characters, a \0 > * separator, and then the filename */ > - s->max_packet_size = (1 /* Tag 70 identifier */ > - + 3 /* Max Tag 70 packet size */ > - + ECRYPTFS_SIG_SIZE /* FNEK sig */ > - + 1 /* Cipher identifier */ > + s->max_packet_size = (ECRYPTFS_TAG_70_MAX_METADATA_SIZE > + s->block_aligned_filename_size); > if (dest == NULL) { > (*packet_size) = s->max_packet_size; > @@ -933,10 +930,10 @@ ecryptfs_parse_tag_70_packet(char **filename, size_t *filename_size, > goto out; > } > s->desc.flags = CRYPTO_TFM_REQ_MAY_SLEEP; > - if (max_packet_size < (1 + 1 + ECRYPTFS_SIG_SIZE + 1 + 1)) { > + if (max_packet_size < ECRYPTFS_TAG_70_MIN_METADATA_SIZE) { > printk(KERN_WARNING "%s: max_packet_size is [%zd]; it must be " > "at least [%d]\n", __func__, max_packet_size, > - (1 + 1 + ECRYPTFS_SIG_SIZE + 1 + 1)); > + ECRYPTFS_TAG_70_MIN_METADATA_SIZE); > rc = -EINVAL; > goto out; > } > diff --git a/fs/ecryptfs/super.c b/fs/ecryptfs/super.c > index dbd52d40..a04d9ef 100644 > --- a/fs/ecryptfs/super.c > +++ b/fs/ecryptfs/super.c > @@ -30,6 +30,8 @@ > #include <linux/seq_file.h> > #include <linux/file.h> > #include <linux/crypto.h> > +#include <linux/statfs.h> > +#include <linux/magic.h> > #include "ecryptfs_kernel.h" > > struct kmem_cache *ecryptfs_inode_info_cache; > @@ -103,10 +105,20 @@ static void ecryptfs_destroy_inode(struct inode *inode) > static int ecryptfs_statfs(struct dentry *dentry, struct kstatfs *buf) > { > struct dentry *lower_dentry = ecryptfs_dentry_to_lower(dentry); > + int rc; > > if (!lower_dentry->d_sb->s_op->statfs) > return -ENOSYS; > - return lower_dentry->d_sb->s_op->statfs(lower_dentry, buf); > + > + rc = lower_dentry->d_sb->s_op->statfs(lower_dentry, buf); > + if (rc) > + return rc; > + > + buf->f_type = ECRYPTFS_SUPER_MAGIC; > + rc = ecryptfs_set_f_namelen(&buf->f_namelen, buf->f_namelen, > + &ecryptfs_superblock_to_private(dentry->d_sb)->mount_crypt_stat); > + > + return rc; > } > > /** -- To unsubscribe from this list: send the line "unsubscribe ecryptfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
