[PATCH 3.2 001/152] eCryptfs: Force RO mount when encrypted view is enabled

Ben Hutchings
2015-02-17T01:46:53Z

From: Tyler Hicks <tyhicks@canonical.com>

commit 332b122d39c9cbff8b799007a825d94b2e7c12f2 upstream.

The ecryptfs_encrypted_view mount option greatly changes the
functionality of an eCryptfs mount. Instead of encrypting and decrypting
lower files, it provides a unified view of the encrypted files in the
lower filesystem. The presence of the ecryptfs_encrypted_view mount
option is intended to force a read-only mount and modifying files is not
supported when the feature is in use. See the following commit for more
information:

e77a56d [PATCH] eCryptfs: Encrypted passthrough

This patch forces the mount to be read-only when the
ecryptfs_encrypted_view mount option is specified by setting the
MS_RDONLY flag on the superblock. Additionally, this patch removes some
broken logic in ecryptfs_open() that attempted to prevent modifications
of files when the encrypted view feature was in use. The check in
ecryptfs_open() was not sufficient to prevent file modifications using
system calls that do not operate on a file descriptor.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Reported-by: Priya Bansal <p.bansal@samsung.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/ecryptfs/file.c | 12 ------------
fs/ecryptfs/main.c | 16 +++++++++++++---
2 files changed, 13 insertions(+), 15 deletions(-)

--- a/fs/ecryptfs/file.c
+++ b/fs/ecryptfs/file.c
@@ -196,24 +196,12 @@ static int ecryptfs_open(struct inode *i
{
int rc = 0;
struct ecryptfs_crypt_stat *crypt_stat = NULL;
- struct ecryptfs_mount_crypt_stat *mount_crypt_stat;
struct dentry *ecryptfs_dentry = file->f_path.dentry;
/* Private value of ecryptfs_dentry allocated in
* ecryptfs_lookup() */
struct dentry *lower_dentry;
struct ecryptfs_file_info *file_info;

- mount_crypt_stat = &ecryptfs_superblock_to_private(
- ecryptfs_dentry->d_sb)->mount_crypt_stat;
- if ((mount_crypt_stat->flags & ECRYPTFS_ENCRYPTED_VIEW_ENABLED)
- && ((file->f_flags & O_WRONLY) || (file->f_flags & O_RDWR)
- || (file->f_flags & O_CREAT) || (file->f_flags & O_TRUNC)
- || (file->f_flags & O_APPEND))) {
- printk(KERN_WARNING "Mount has encrypted view enabled; "
- "files may only be read\n");
- rc = -EPERM;
- goto out;
- }
/* Released in ecryptfs_release or end of function if failure */
file_info = kmem_cache_zalloc(ecryptfs_file_info_cache, GFP_KERNEL);
ecryptfs_set_file_private(file, file_info);
--- a/fs/ecryptfs/main.c
+++ b/fs/ecryptfs/main.c
@@ -494,6 +494,7 @@ static struct dentry *ecryptfs_mount(str
{
struct super_block *s;
struct ecryptfs_sb_info *sbi;
+ struct ecryptfs_mount_crypt_stat *mount_crypt_stat;
struct ecryptfs_dentry_info *root_info;
const char *err = "Getting sb failed";
struct inode *inode;
@@ -512,6 +513,7 @@ static struct dentry *ecryptfs_mount(str
err = "Error parsing options";
goto out;
}
+ mount_crypt_stat = &sbi->mount_crypt_stat;

s = sget(fs_type, NULL, set_anon_super, NULL);
if (IS_ERR(s)) {
@@ -557,11 +559,19 @@ static struct dentry *ecryptfs_mount(str

/**
* Set the POSIX ACL flag based on whether they're enabled in the lower
- * mount. Force a read-only eCryptfs mount if the lower mount is ro.
- * Allow a ro eCryptfs mount even when the lower mount is rw.
+ * mount.
*/
s->s_flags = flags & ~MS_POSIXACL;
- s->s_flags |= path.dentry->d_sb->s_flags & (MS_RDONLY | MS_POSIXACL);
+ s->s_flags |= path.dentry->d_sb->s_flags & MS_POSIXACL;
+
+ /**
+ * Force a read-only eCryptfs mount when:
+ * 1) The lower mount is ro
+ * 2) The ecryptfs_encrypted_view mount option is specified
+ */
+ if (path.dentry->d_sb->s_flags & MS_RDONLY ||
+ mount_crypt_stat->flags & ECRYPTFS_ENCRYPTED_VIEW_ENABLED)
+ s->s_flags |= MS_RDONLY;

s->s_maxbytes = path.dentry->d_sb->s_maxbytes;
s->s_blocksize = path.dentry->d_sb->s_blocksize;