[PATCH 2/3 v2] eCryptfs: Check inode changes in setattr

[Tyler Hicks <tyhicks@canonical.com>]

Most filesystems call inode_change_ok() very early in ->setattr(), but
eCryptfs didn't call it at all. It allowed the lower filesystem to make
the call in its ->setattr() function. Then, eCryptfs would copy the
appropriate inode attributes from the lower inode to the eCryptfs inode.

This patch changes that and actually calls inode_change_ok() on the
eCryptfs inode, fairly early in ecryptfs_setattr(). Ideally, the call
would happen earlier in ecryptfs_setattr(), but there are some possible
inode initialization steps that must happen first.

Since the call was already being made on the lower inode, the change in
functionality should be minimal, except for the case of a file extending
truncate call. In that case, inode_newsize_ok() was never being
called on the eCryptfs inode. Rather than inode_newsize_ok() catching
maximum file size errors early on, eCryptfs would encrypt zeroed pages
and write them to the lower filesystem until the lower filesystem's
write path caught the error in generic_write_checks(). This patch
introduces a new function, called ecryptfs_inode_newsize_ok(), which
checks if the new lower file size is within the appropriate limits when
the truncate operation will be growing the lower file.

In summary this change prevents eCryptfs truncate operations (and the
resulting page encryptions), which would exceed the lower filesystem
limits or FSIZE rlimits, from ever starting.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Cc: <stable@vger.kernel.org>
---

Linus, this is still in the out-for-comments stage. I'll be preparing a pull
request soon.

Changes from v1:
 - Added ecryptfs_inode_newsize_ok() to help with detecting when inode_newsize_ok()
   needs to be called and to pass the appropriate offset parameter to that function
 - Minor touchups to the commit message

 fs/ecryptfs/inode.c |   48 ++++++++++++++++++++++++++++++++++++------------
 1 files changed, 36 insertions(+), 12 deletions(-)

diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
index 19a8ca4..19892d7 100644
--- a/fs/ecryptfs/inode.c
+++ b/fs/ecryptfs/inode.c
@@ -822,18 +822,6 @@ static int truncate_upper(struct dentry *dentry, struct iattr *ia,
 		size_t num_zeros = (PAGE_CACHE_SIZE
 				    - (ia->ia_size & ~PAGE_CACHE_MASK));
 
-
-		/*
-		 * XXX(truncate) this should really happen at the begginning
-		 * of ->setattr.  But the code is too messy to that as part
-		 * of a larger patch.  ecryptfs is also totally missing out
-		 * on the inode_change_ok check at the beginning of
-		 * ->setattr while would include this.
-		 */
-		rc = inode_newsize_ok(inode, ia->ia_size);
-		if (rc)
-			goto out;
-
 		if (!(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {
 			truncate_setsize(inode, ia->ia_size);
 			lower_ia->ia_size = ia->ia_size;
@@ -883,6 +871,28 @@ out:
 	return rc;
 }
 
+static int ecryptfs_inode_newsize_ok(struct inode *inode, loff_t offset)
+{
+	struct ecryptfs_crypt_stat *crypt_stat;
+	loff_t lower_oldsize, lower_newsize;
+
+	crypt_stat = &ecryptfs_inode_to_private(inode)->crypt_stat;
+	lower_oldsize = upper_size_to_lower_size(crypt_stat,
+						 i_size_read(inode));
+	lower_newsize = upper_size_to_lower_size(crypt_stat, offset);
+	if (lower_newsize > lower_oldsize) {
+		/*
+		 * The eCryptfs inode and the new *lower* size are mixed here
+		 * because we may not have the lower i_mutex held and/or it may
+		 * not be appropriate to call inode_newsize_ok() with inodes
+		 * from other filesystems.
+		 */
+		return inode_newsize_ok(inode, lower_newsize);
+	}
+
+	return 0;
+}
+
 /**
  * ecryptfs_truncate
  * @dentry: The ecryptfs layer dentry
@@ -899,6 +909,10 @@ int ecryptfs_truncate(struct dentry *dentry, loff_t new_length)
 	struct iattr lower_ia = { .ia_valid = 0 };
 	int rc;
 
+	rc = ecryptfs_inode_newsize_ok(dentry->d_inode, new_length);
+	if (rc)
+		return rc;
+
 	rc = truncate_upper(dentry, &ia, &lower_ia);
 	if (!rc && lower_ia.ia_valid & ATTR_SIZE) {
 		struct dentry *lower_dentry = ecryptfs_dentry_to_lower(dentry);
@@ -978,6 +992,16 @@ static int ecryptfs_setattr(struct dentry *dentry, struct iattr *ia)
 		}
 	}
 	mutex_unlock(&crypt_stat->cs_mutex);
+
+	rc = inode_change_ok(inode, ia);
+	if (rc)
+		goto out;
+	if (ia->ia_valid & ATTR_SIZE) {
+		rc = ecryptfs_inode_newsize_ok(inode, ia->ia_size);
+		if (rc)
+			goto out;
+	}
+
 	if (S_ISREG(inode->i_mode)) {
 		rc = filemap_write_and_wait(inode->i_mapping);
 		if (rc)
-- 
1.7.8.3