Commit c01638f5 authored Dec 06, 2016 by Miklos Szeredi

fuse: fix clearing suid, sgid for chown()



Basically, the pjdfstests set the ownership of a file to 06555, and then
chowns it (as root) to a new uid/gid. Prior to commit a09f99ed ("fuse:
fix killing s[ug]id in setattr"), fuse would send down a setattr with both
the uid/gid change and a new mode.  Now, it just sends down the uid/gid
change.

Technically this is NOTABUG, since POSIX doesn't _require_ that we clear
these bits for a privileged process, but Linux (wisely) has done that and I
think we don't want to change that behavior here.

This is caused by the use of should_remove_suid(), which will always return
0 when the process has CAP_FSETID.

In fact we really don't need to be calling should_remove_suid() at all,
since we've already been indicated that we should remove the suid, we just
don't want to use a (very) stale mode for that.

This patch should fix the above as well as simplify the logic.

Reported-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: a09f99ed ("fuse: fix killing s[ug]id in setattr")
Cc: <stable@vger.kernel.org>
Reviewed-by: Jeff Layton <jlayton@redhat.com>

parent 3e5de27e

fs/fuse/dir.c

+2 −5

Original line number	Diff line number	Diff line
		@@ -1739,8 +1739,6 @@ static int fuse_setattr(struct dentry entry, struct iattr attr)
		* This should be done on write(), truncate() and chown().
		*/
		if (!fc->handle_killpriv) {
		int kill;

		/*
		* ia_mode calculation may have used stale i_mode.
		* Refresh and recalculate.
		@@ -1750,12 +1748,11 @@ static int fuse_setattr(struct dentry entry, struct iattr attr)
		return ret;

		attr->ia_mode = inode->i_mode;
		kill = should_remove_suid(entry);
		if (kill & ATTR_KILL_SUID) {
		if (inode->i_mode & S_ISUID) {
		attr->ia_valid \|= ATTR_MODE;
		attr->ia_mode &= ~S_ISUID;
		}
		if (kill & ATTR_KILL_SGID) {
		if ((inode->i_mode & (S_ISGID \| S_IXGRP)) == (S_ISGID \| S_IXGRP)) {
		attr->ia_valid \|= ATTR_MODE;
		attr->ia_mode &= ~S_ISGID;
		}