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NFS: Fix a potential file corruption issue when writing

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If the inode is flagged as having an invalid mapping, then we can't rely on
the PageUptodate() flag. Ensure that we don't use the "anti-fragmentation"
write optimisation in nfs_updatepage(), since that will cause NFS to write
out areas of the page that are no longer guaranteed to be up to date.

A potential corruption could occur in the following scenario:

client 1			client 2
===============			===============
				fd=open("f",O_CREAT|O_WRONLY,0644);
				write(fd,"fubar\n",6);	// cache last page
				close(fd);
fd=open("f",O_WRONLY|O_APPEND);
write(fd,"foo\n",4);
close(fd);

				fd=open("f",O_WRONLY|O_APPEND);
				write(fd,"bar\n",4);
				close(fd);
-----
The bug may lead to the file "f" reading 'fubar\n\0\0\0\nbar\n' because
client 2 does not update the cached page after re-opening the file for
write. Instead it keeps it marked as PageUptodate() until someone calls
invaldate_inode_pages2() (typically by calling read()).

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
This commit is contained in:
Trond Myklebust 2008-02-07 17:24:07 -05:00
parent df922075f2
commit 5d47a35600
1 changed files with 17 additions and 3 deletions
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20
fs/nfs/write.c
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@ -696,6 +696,17 @@ int nfs_flush_incompatible(struct file *file, struct page *page)
return status;
}
/*
* If the page cache is marked as unsafe or invalid, then we can't rely on
* the PageUptodate() flag. In this case, we will need to turn off
* write optimisations that depend on the page contents being correct.
*/
static int nfs_write_pageuptodate(struct page *page, struct inode *inode)
{
return PageUptodate(page) &&
!(NFS_I(inode)->cache_validity & (NFS_INO_REVAL_PAGECACHE|NFS_INO_INVALID_DATA));
}
/*
* Update and possibly write a cached page of an NFS file.
*
@ -717,10 +728,13 @@ int nfs_updatepage(struct file *file, struct page *page,
(long long)(page_offset(page) +offset));
/* If we're not using byte range locks, and we know the page
* is entirely in cache, it may be more efficient to avoid
* fragmenting write requests.
* is up to date, it may be more efficient to extend the write
* to cover the entire page in order to avoid fragmentation
* inefficiencies.
*/
if (PageUptodate(page) && inode->i_flock == NULL && !(file->f_mode & O_SYNC)) {
if (nfs_write_pageuptodate(page, inode) &&
inode->i_flock == NULL &&
!(file->f_mode & O_SYNC)) {
count = max(count + offset, nfs_page_length(page));
offset = 0;
}