Commit a09f99ed authored by Miklos Szeredi's avatar Miklos Szeredi
Browse files

fuse: fix killing s[ug]id in setattr 



Fuse allowed VFS to set mode in setattr in order to clear suid/sgid on
chown and truncate, and (since writeback_cache) write.  The problem with
this is that it'll potentially restore a stale mode.

The poper fix would be to let the filesystems do the suid/sgid clearing on
the relevant operations.  Possibly some are already doing it but there's no
way we can detect this.

So fix this by refreshing and recalculating the mode.  Do this only if
ATTR_KILL_S[UG]ID is set to not destroy performance for writes.  This is
still racy but the size of the window is reduced.

Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org>
parent 5e2b8828

fs/fuse/dir.c

+28 −4
Original line number Diff line number Diff line
@@ -1703,16 +1703,40 @@ error: 
static int fuse_setattr(struct dentry *entry, struct iattr *attr)

{

	struct inode *inode = d_inode(entry);

	struct file *file = (attr->ia_valid & ATTR_FILE) ? attr->ia_file : NULL;

	int ret;



	if (!fuse_allow_current_process(get_fuse_conn(inode)))

		return -EACCES;



	if (attr->ia_valid & ATTR_FILE)

		ret = fuse_do_setattr(inode, attr, attr->ia_file);

	else

		ret = fuse_do_setattr(inode, attr, NULL);

	if (attr->ia_valid & (ATTR_KILL_SUID | ATTR_KILL_SGID)) {

		int kill;



		attr->ia_valid &= ~(ATTR_KILL_SUID | ATTR_KILL_SGID |

				    ATTR_MODE);

		/*

		 * ia_mode calculation may have used stale i_mode.  Refresh and

		 * recalculate.

		 */

		ret = fuse_do_getattr(inode, NULL, file);

		if (ret)

			return ret;



		attr->ia_mode = inode->i_mode;

		kill = should_remove_suid(entry);

		if (kill & ATTR_KILL_SUID) {

			attr->ia_valid |= ATTR_MODE;

			attr->ia_mode &= ~S_ISUID;

		}

		if (kill & ATTR_KILL_SGID) {

			attr->ia_valid |= ATTR_MODE;

			attr->ia_mode &= ~S_ISGID;

		}

	}

	if (!attr->ia_valid)

		return 0;



	ret = fuse_do_setattr(inode, attr, file);

	if (!ret) {

		/* Directory mode changed, may need to revalidate access */

		if (d_is_dir(entry) && (attr->ia_valid & ATTR_MODE))

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