Commit b24e7598 authored Oct 23, 2019 by Miklos Szeredi

fuse: flush dirty data/metadata before non-truncate setattr



If writeback cache is enabled, then writes might get reordered with
chmod/chown/utimes.  The problem with this is that performing the write in
the fuse daemon might itself change some of these attributes.  In such case
the following sequence of operations will result in file ending up with the
wrong mode, for example:

  int fd = open ("suid", O_WRONLY|O_CREAT|O_EXCL);
  write (fd, "1", 1);
  fchown (fd, 0, 0);
  fchmod (fd, 04755);
  close (fd);

This patch fixes this by flushing pending writes before performing
chown/chmod/utimes.

Reported-by: Giuseppe Scrivano <gscrivan@redhat.com>
Tested-by: Giuseppe Scrivano <gscrivan@redhat.com>
Fixes: 4d99ff8f ("fuse: Turn writeback cache on")
Cc: <stable@vger.kernel.org> # v3.15+
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

parent 80da5a80

fs/fuse/dir.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -1522,6 +1522,19 @@ int fuse_do_setattr(struct dentry dentry, struct iattr attr,
		is_truncate = true;
		}

		/* Flush dirty data/metadata before non-truncate SETATTR */
		if (is_wb && S_ISREG(inode->i_mode) &&
		attr->ia_valid &
		(ATTR_MODE \| ATTR_UID \| ATTR_GID \| ATTR_MTIME_SET \|
		ATTR_TIMES_SET)) {
		err = write_inode_now(inode, true);
		if (err)
		return err;

		fuse_set_nowrite(inode);
		fuse_release_nowrite(inode);
		}

		if (is_truncate) {
		fuse_set_nowrite(inode);
		set_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);

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