eCryptfs: make ecryptfs_prepare_write decrypt the page

When the page is not up to date, ecryptfs_prepare_write() should be
acting much like ecryptfs_readpage(). This includes the painfully
obvious step of actually decrypting the page contents read from the
lower encrypted file.

Note that this patch resolves a bug in eCryptfs in 2.6.24 that one can
produce with these steps:

# mount -t ecryptfs /secret /secret
# echo "abc" > /secret/file.txt
# umount /secret
# mount -t ecryptfs /secret /secret
# echo "def" >> /secret/file.txt
# cat /secret/file.txt

Without this patch, the resulting data returned from cat is likely to
be something other than "abc\ndef\n".

(Thanks to Benedikt Driessen for reporting this.)

Signed-off-by: Michael Halcrow <mhalcrow@us.ibm.com>
Cc: Benedikt Driessen <bdriessen@escrypt.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 76 insertions, 26 deletions

diff --git a/fs/ecryptfs/mmap.c b/fs/ecryptfs/mmap.c
index dc74b186145..6df1debdccc 100644
--- a/fs/ecryptfs/mmap.c
+++ b/fs/ecryptfs/mmap.c
@@ -263,52 +263,102 @@ out:
         return 0;
 }
 
-/* This function must zero any hole we create */
+/**
+ * ecryptfs_prepare_write
+ * @file: The eCryptfs file
+ * @page: The eCryptfs page
+ * @from: The start byte from which we will write
+ * @to: The end byte to which we will write
+ *
+ * This function must zero any hole we create
+ *
+ * Returns zero on success; non-zero otherwise
+ */
 static int ecryptfs_prepare_write(struct file *file, struct page *page,
                                   unsigned from, unsigned to)
 {
-        int rc = 0;
         loff_t prev_page_end_size;
+        int rc = 0;
 
         if (!PageUptodate(page)) {
-                rc = ecryptfs_read_lower_page_segment(page, page->index, 0,
-                                                      PAGE_CACHE_SIZE,
-                                                      page->mapping->host);
-                if (rc) {
-                        printk(KERN_ERR "%s: Error attemping to read lower "
-                               "page segment; rc = [%d]\n", __FUNCTION__, rc);
-                        ClearPageUptodate(page);
-                        goto out;
-                } else
+                struct ecryptfs_crypt_stat *crypt_stat =
+                        &ecryptfs_inode_to_private(
+                                file->f_path.dentry->d_inode)->crypt_stat;
+
+                if (!(crypt_stat->flags & ECRYPTFS_ENCRYPTED)
+                    || (crypt_stat->flags & ECRYPTFS_NEW_FILE)) {
+                        rc = ecryptfs_read_lower_page_segment(
+                                page, page->index, 0, PAGE_CACHE_SIZE,
+                                page->mapping->host);
+                        if (rc) {
+                                printk(KERN_ERR "%s: Error attemping to read "
+                                       "lower page segment; rc = [%d]\n",
+                                       __FUNCTION__, rc);
+                                ClearPageUptodate(page);
+                                goto out;
+                        } else
+                                SetPageUptodate(page);
+                } else if (crypt_stat->flags & ECRYPTFS_VIEW_AS_ENCRYPTED) {
+                        if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {
+                                rc = ecryptfs_copy_up_encrypted_with_header(
+                                        page, crypt_stat);
+                                if (rc) {
+                                        printk(KERN_ERR "%s: Error attempting "
+                                               "to copy the encrypted content "
+                                               "from the lower file whilst "
+                                               "inserting the metadata from "
+                                               "the xattr into the header; rc "
+                                               "= [%d]\n", __FUNCTION__, rc);
+                                        ClearPageUptodate(page);
+                                        goto out;
+                                }
+                                SetPageUptodate(page);
+                        } else {
+                                rc = ecryptfs_read_lower_page_segment(
+                                        page, page->index, 0, PAGE_CACHE_SIZE,
+                                        page->mapping->host);
+                                if (rc) {
+                                        printk(KERN_ERR "%s: Error reading "
+                                               "page; rc = [%d]\n",
+                                               __FUNCTION__, rc);
+                                        ClearPageUptodate(page);
+                                        goto out;
+                                }
+                                SetPageUptodate(page);
+                        }
+                } else {
+                        rc = ecryptfs_decrypt_page(page);
+                        if (rc) {
+                                printk(KERN_ERR "%s: Error decrypting page "
+                                       "at index [%ld]; rc = [%d]\n",
+                                       __FUNCTION__, page->index, rc);
+                                ClearPageUptodate(page);
+                                goto out;
+                        }
                         SetPageUptodate(page);
+                }
         }
-
         prev_page_end_size = ((loff_t)page->index << PAGE_CACHE_SHIFT);
-
-        /*
-         * If creating a page or more of holes, zero them out via truncate.
-         * Note, this will increase i_size.
-         */
+        /* If creating a page or more of holes, zero them out via truncate.
+         * Note, this will increase i_size. */
         if (page->index != 0) {
                 if (prev_page_end_size > i_size_read(page->mapping->host)) {
                         rc = ecryptfs_truncate(file->f_path.dentry,
                                                prev_page_end_size);
                         if (rc) {
-                                printk(KERN_ERR "Error on attempt to "
+                                printk(KERN_ERR "%s: Error on attempt to "
                                        "truncate to (higher) offset [%lld];"
-                                       " rc = [%d]\n", prev_page_end_size, rc);
+                                       " rc = [%d]\n", __FUNCTION__,
+                                       prev_page_end_size, rc);
                                 goto out;
                         }
                 }
         }
-        /*
-         * Writing to a new page, and creating a small hole from start of page?
-         * Zero it out.
-         */
-        if ((i_size_read(page->mapping->host) == prev_page_end_size) &&
-            (from != 0)) {
+        /* Writing to a new page, and creating a small hole from start
+         * of page?  Zero it out. */
+        if ((i_size_read(page->mapping->host) == prev_page_end_size)
+            && (from != 0))
                 zero_user(page, 0, PAGE_CACHE_SIZE);
-        }
 out:
         return rc;
 }