Commit 53a2731f authored by Michael Halcrow's avatar Michael Halcrow Committed by Linus Torvalds

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: 's avatarMichael Halcrow <mhalcrow@us.ibm.com>
Signed-off-by: 's avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4acb3e2f
......@@ -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,
......
......@@ -376,9 +376,31 @@ static int fill_zeros_to_end_of_page(struct page *page, unsigned int to)
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;
......
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