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>

diff --git a/fs/ecryptfs/file.c b/fs/ecryptfs/file.c
index 9881b5c5de59b6f564435cc26dc17f5a638e32bc..59288d817078879ad36c1ece17a51208488d571e 100644 (file)
--- a/fs/ecryptfs/file.c
+++ b/fs/ecryptfs/file.c
@@ -32,63 +32,6 @@
 #include <linux/fs_stack.h>
 #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
  *
@@ -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 88ea6697908f511a1eadeffc4ee04ce3f9f93cf4..55cec98a84e75cf490143af46302a9495993f158 100644 (file)
--- 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;