@@ -1354,6 +1354,7 @@ static int fuse_do_setattr(struct dentry *entry, struct iattr *attr,
{
struct inode *inode = entry->d_inode;
struct fuse_conn *fc = get_fuse_conn(inode);
+ struct fuse_inode *fi = get_fuse_inode(inode);
struct fuse_req *req;
struct fuse_setattr_in inarg;
struct fuse_attr_out outarg;
@@ -1384,8 +1385,10 @@ static int fuse_do_setattr(struct dentry *entry, struct iattr *attr,
if (IS_ERR(req))
return PTR_ERR(req);
- if (is_truncate)
+ if (is_truncate) {
fuse_set_nowrite(inode);
+ set_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
+ }
memset(&inarg, 0, sizeof(inarg));
memset(&outarg, 0, sizeof(outarg));
@@ -1447,12 +1450,14 @@ static int fuse_do_setattr(struct dentry *entry, struct iattr *attr,
invalidate_inode_pages2(inode->i_mapping);
}
+ clear_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
return 0;
error:
if (is_truncate)
fuse_release_nowrite(inode);
+ clear_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
return err;
}
@@ -515,7 +515,8 @@ static void fuse_read_update_size(struct inode *inode, loff_t size,
struct fuse_inode *fi = get_fuse_inode(inode);
spin_lock(&fc->lock);
- if (attr_ver == fi->attr_version && size < inode->i_size) {
+ if (attr_ver == fi->attr_version && size < inode->i_size &&
+ !test_bit(FUSE_I_SIZE_UNSTABLE, &fi->state)) {
fi->attr_version = ++fc->attr_version;
i_size_write(inode, size);
}
@@ -877,12 +878,16 @@ static ssize_t fuse_perform_write(struct file *file,
{
struct inode *inode = mapping->host;
struct fuse_conn *fc = get_fuse_conn(inode);
+ struct fuse_inode *fi = get_fuse_inode(inode);
int err = 0;
ssize_t res = 0;
if (is_bad_inode(inode))
return -EIO;
+ if (inode->i_size < pos + iov_iter_count(ii))
+ set_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
+
do {
struct fuse_req *req;
ssize_t count;
@@ -917,6 +922,7 @@ static ssize_t fuse_perform_write(struct file *file,
if (res > 0)
fuse_write_update_size(inode, pos);
+ clear_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
fuse_invalidate_attr(inode);
return res > 0 ? res : err;
@@ -103,6 +103,15 @@ struct fuse_inode {
/** List of writepage requestst (pending or sent) */
struct list_head writepages;
+
+ /** Miscellaneous bits describing inode state */
+ unsigned long state;
+};
+
+/** FUSE inode state bits */
+enum {
+ /** An operation changing file size is in progress */
+ FUSE_I_SIZE_UNSTABLE,
};
struct fuse_conn;
@@ -92,6 +92,7 @@ static struct inode *fuse_alloc_inode(struct super_block *sb)
fi->attr_version = 0;
fi->writectr = 0;
fi->orig_ino = 0;
+ fi->state = 0;
INIT_LIST_HEAD(&fi->write_files);
INIT_LIST_HEAD(&fi->queued_writes);
INIT_LIST_HEAD(&fi->writepages);
@@ -199,7 +200,8 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
loff_t oldsize;
spin_lock(&fc->lock);
- if (attr_version != 0 && fi->attr_version > attr_version) {
+ if ((attr_version != 0 && fi->attr_version > attr_version) ||
+ test_bit(FUSE_I_SIZE_UNSTABLE, &fi->state)) {
spin_unlock(&fc->lock);
return;
}
This is a note to let you know that I have just added a patch titled fuse: hotfix truncate_pagecache() issue to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.5.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From 8c1bd169ed19cdbce72b9289d9898c8d5a1eb687 Mon Sep 17 00:00:00 2001 From: Maxim Patlasov <MPatlasov@parallels.com> Date: Fri, 30 Aug 2013 17:06:04 +0400 Subject: [PATCH] fuse: hotfix truncate_pagecache() issue commit 06a7c3c2781409af95000c60a5df743fd4e2f8b4 upstream. The way how fuse calls truncate_pagecache() from fuse_change_attributes() is completely wrong. Because, w/o i_mutex held, we never sure whether 'oldsize' and 'attr->size' are valid by the time of execution of truncate_pagecache(inode, oldsize, attr->size). In fact, as soon as we released fc->lock in the middle of fuse_change_attributes(), we completely loose control of actions which may happen with given inode until we reach truncate_pagecache. The list of potentially dangerous actions includes mmap-ed reads and writes, ftruncate(2) and write(2) extending file size. The typical outcome of doing truncate_pagecache() with outdated arguments is data corruption from user point of view. This is (in some sense) acceptable in cases when the issue is triggered by a change of the file on the server (i.e. externally wrt fuse operation), but it is absolutely intolerable in scenarios when a single fuse client modifies a file without any external intervention. A real life case I discovered by fsx-linux looked like this: 1. Shrinking ftruncate(2) comes to fuse_do_setattr(). The latter sends FUSE_SETATTR to the server synchronously, but before getting fc->lock ... 2. fuse_dentry_revalidate() is asynchronously called. It sends FUSE_LOOKUP to the server synchronously, then calls fuse_change_attributes(). The latter updates i_size, releases fc->lock, but before comparing oldsize vs attr->size.. 3. fuse_do_setattr() from the first step proceeds by acquiring fc->lock and updating attributes and i_size, but now oldsize is equal to outarg.attr.size because i_size has just been updated (step 2). Hence, fuse_do_setattr() returns w/o calling truncate_pagecache(). 4. As soon as ftruncate(2) completes, the user extends file size by write(2) making a hole in the middle of file, then reads data from the hole either by read(2) or mmap-ed read. The user expects to get zero data from the hole, but gets stale data because truncate_pagecache() is not executed yet. The scenario above illustrates one side of the problem: not truncating the page cache even though we should. Another side corresponds to truncating page cache too late, when the state of inode changed significantly. Theoretically, the following is possible: 1. As in the previous scenario fuse_dentry_revalidate() discovered that i_size changed (due to our own fuse_do_setattr()) and is going to call truncate_pagecache() for some 'new_size' it believes valid right now. But by the time that particular truncate_pagecache() is called ... 2. fuse_do_setattr() returns (either having called truncate_pagecache() or not -- it doesn't matter). 3. The file is extended either by write(2) or ftruncate(2) or fallocate(2). 4. mmap-ed write makes a page in the extended region dirty. The result will be the lost of data user wrote on the fourth step. The patch is a hotfix resolving the issue in a simplistic way: let's skip dangerous i_size update and truncate_pagecache if an operation changing file size is in progress. This simplistic approach looks correct for the cases w/o external changes. And to handle them properly, more sophisticated and intrusive techniques (e.g. NFS-like one) would be required. I'd like to postpone it until the issue is well discussed on the mailing list(s). Changed in v2: - improved patch description to cover both sides of the issue. Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> [ luis: backported to 3.5, based on bwh's backport to 3.2: - added state field to struct fuse_inode ] Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- fs/fuse/dir.c | 7 ++++++- fs/fuse/file.c | 8 +++++++- fs/fuse/fuse_i.h | 9 +++++++++ fs/fuse/inode.c | 4 +++- 4 files changed, 25 insertions(+), 3 deletions(-) -- 1.8.3.2