Commit 14c14414 authored Jun 13, 2013 by Maxim Patlasov Committed by Miklos Szeredi Jun 18, 2013

fuse: hold i_mutex in fuse_file_fallocate()



Changing size of a file on server and local update (fuse_write_update_size)
should be always protected by inode->i_mutex. Otherwise a race like this is
possible:

1. Process 'A' calls fallocate(2) to extend file (~FALLOC_FL_KEEP_SIZE).
fuse_file_fallocate() sends FUSE_FALLOCATE request to the server.
2. Process 'B' calls ftruncate(2) shrinking the file. fuse_do_setattr()
sends shrinking FUSE_SETATTR request to the server and updates local i_size
by i_size_write(inode, outarg.attr.size).
3. Process 'A' resumes execution of fuse_file_fallocate() and calls
fuse_write_update_size(inode, offset + length). But 'offset + length' was
obsoleted by ftruncate from previous step.

Changed in v2 (thanks Brian and Anand for suggestions):
 - made relation between mutex_lock() and fuse_set_nowrite(inode) more
   explicit and clear.
 - updated patch description to use ftruncate(2) in example

Signed-off-by: Maxim V. Patlasov <MPatlasov@parallels.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

parent 8177a9d7

fs/fuse/file.c

+8 −4

Original line number	Diff line number	Diff line
		@@ -2470,12 +2470,15 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
		.mode = mode
		};
		int err;
		bool lock_inode = !(mode & FALLOC_FL_KEEP_SIZE) \|\|
		(mode & FALLOC_FL_PUNCH_HOLE);

		if (fc->no_fallocate)
		return -EOPNOTSUPP;

		if (mode & FALLOC_FL_PUNCH_HOLE) {
		if (lock_inode) {
		mutex_lock(&inode->i_mutex);
		if (mode & FALLOC_FL_PUNCH_HOLE)
		fuse_set_nowrite(inode);
		}

		@@ -2511,7 +2514,8 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
		fuse_invalidate_attr(inode);

		out:
		if (mode & FALLOC_FL_PUNCH_HOLE) {
		if (lock_inode) {
		if (mode & FALLOC_FL_PUNCH_HOLE)
		fuse_release_nowrite(inode);
		mutex_unlock(&inode->i_mutex);
		}