eCryptfs: delay writing 0's after llseek until write

Delay writing 0's out in eCryptfs after a seek past the end of the file
until data is actually written.

http://www.opengroup.org/onlinepubs/009695399/functions/lseek.html

``The lseek() function shall not, by itself, extend the size of a
file.''

Without this fix, applications that lseek() past the end of the file without
writing will experience unexpected behavior.

Signed-off-by: Michael Halcrow <mhalcrow@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 36 insertions, 61 deletions

diff --git a/fs/ecryptfs/file.c b/fs/ecryptfs/file.c
index 9881b5c5de59..59288d817078 100644
--- a/fs/ecryptfs/file.c
+++ b/fs/ecryptfs/file.c
@@ -33,63 +33,6 @@
 #include "ecryptfs_kernel.h"
 
 /**
- * ecryptfs_llseek
- * @file: File we are seeking in
- * @offset: The offset to seek to
- * @origin: 2 - offset from i_size; 1 - offset from f_pos
- *
- * Returns the position we have seeked to, or negative on error
- */
-static loff_t ecryptfs_llseek(struct file *file, loff_t offset, int origin)
-{
-        loff_t rv;
-        loff_t new_end_pos;
-        int rc;
-        int expanding_file = 0;
-        struct inode *inode = file->f_mapping->host;
-
-        /* If our offset is past the end of our file, we're going to
-         * need to grow it so we have a valid length of 0's */
-        new_end_pos = offset;
-        switch (origin) {
-        case 2:
-                new_end_pos += i_size_read(inode);
-                expanding_file = 1;
-                break;
-        case 1:
-                new_end_pos += file->f_pos;
-                if (new_end_pos > i_size_read(inode)) {
-                        ecryptfs_printk(KERN_DEBUG, "new_end_pos(=[0x%.16x]) "
-                                        "> i_size_read(inode)(=[0x%.16x])\n",
-                                        new_end_pos, i_size_read(inode));
-                        expanding_file = 1;
-                }
-                break;
-        default:
-                if (new_end_pos > i_size_read(inode)) {
-                        ecryptfs_printk(KERN_DEBUG, "new_end_pos(=[0x%.16x]) "
-                                        "> i_size_read(inode)(=[0x%.16x])\n",
-                                        new_end_pos, i_size_read(inode));
-                        expanding_file = 1;
-                }
-        }
-        ecryptfs_printk(KERN_DEBUG, "new_end_pos = [0x%.16x]\n", new_end_pos);
-        if (expanding_file) {
-                rc = ecryptfs_truncate(file->f_path.dentry, new_end_pos);
-                if (rc) {
-                        rv = rc;
-                        ecryptfs_printk(KERN_ERR, "Error on attempt to "
-                                        "truncate to (higher) offset [0x%.16x];"
-                                        " rc = [%d]\n", new_end_pos, rc);
-                        goto out;
-                }
-        }
-        rv = generic_file_llseek(file, offset, origin);
-out:
-        return rv;
-}
-
-/**
  * ecryptfs_read_update_atime
  *
  * generic_file_read updates the atime of upper layer inode.  But, it
@@ -425,7 +368,7 @@ const struct file_operations ecryptfs_dir_fops = {
 };
 
 const struct file_operations ecryptfs_main_fops = {
-        .llseek = ecryptfs_llseek,
+        .llseek = generic_file_llseek,
         .read = do_sync_read,
         .aio_read = ecryptfs_read_update_atime,
         .write = do_sync_write,
diff --git a/fs/ecryptfs/mmap.c b/fs/ecryptfs/mmap.c
index 88ea6697908f..55cec98a84e7 100644
--- a/fs/ecryptfs/mmap.c
+++ b/fs/ecryptfs/mmap.c
@@ -376,9 +376,31 @@ out:
         return 0;
 }
 
+/**
+ * eCryptfs does not currently support holes. When writing after a
+ * seek past the end of the file, eCryptfs fills in 0's through to the
+ * current location. The code to fill in the 0's to all the
+ * intermediate pages calls ecryptfs_prepare_write_no_truncate().
+ */
+static int
+ecryptfs_prepare_write_no_truncate(struct file *file, struct page *page,
+                                   unsigned from, unsigned to)
+{
+        int rc = 0;
+
+        if (from == 0 && to == PAGE_CACHE_SIZE)
+                goto out;       /* If we are writing a full page, it will be
+                                   up to date. */
+        if (!PageUptodate(page))
+                rc = ecryptfs_do_readpage(file, page, page->index);
+out:
+        return rc;
+}
+
 static int ecryptfs_prepare_write(struct file *file, struct page *page,
                                   unsigned from, unsigned to)
 {
+        loff_t pos;
         int rc = 0;
 
         if (from == 0 && to == PAGE_CACHE_SIZE)
@@ -386,6 +408,16 @@ static int ecryptfs_prepare_write(struct file *file, struct page *page,
                                    up to date. */
         if (!PageUptodate(page))
                 rc = ecryptfs_do_readpage(file, page, page->index);
+        pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
+        if (pos > i_size_read(page->mapping->host)) {
+                rc = ecryptfs_truncate(file->f_path.dentry, pos);
+                if (rc) {
+                        printk(KERN_ERR "Error on attempt to "
+                               "truncate to (higher) offset [%lld];"
+                               " rc = [%d]\n", pos, rc);
+                        goto out;
+                }
+        }
 out:
         return rc;
 }
@@ -744,10 +776,10 @@ int write_zeros(struct file *file, pgoff_t index, int start, int num_zeros)
                 rc = PTR_ERR(tmp_page);
                 goto out;
         }
-        rc = ecryptfs_prepare_write(file, tmp_page, start, start + num_zeros);
-        if (rc) {
+        if ((rc = ecryptfs_prepare_write_no_truncate(file, tmp_page, start,
+                                                     (start + num_zeros)))) {
                 ecryptfs_printk(KERN_ERR, "Error preparing to write zero's "
-                                "to remainder of page at index [0x%.16x]\n",
+                                "to page at index [0x%.16x]\n",
                                 index);
                 page_cache_release(tmp_page);
                 goto out;