On Tue, Dec 06, 2016 at 07:13:25AM -0500, Jeff Layton wrote:
> Should we be checking that the latest i_mode even has these bits before
> sending down the mode change?
Fixed, see updated patch below.
It also fixes a bug in the previous patch where in case of "-rwsrwSr-x" it would
clear the sgid bit without execute.
>
> > > + attr->ia_mode = inode->i_mode & ~(S_ISUID | S_ISGID);
> > + attr->ia_valid |= ATTR_MODE;
> > }
> > }
> > if (!attr->ia_valid)
>
> Yeah that is quite a bit simpler.
>
> That said...if either ATTR_KILL flag is set, then we're going to end up
> clearing both bits in the new mode. I guess that's ok since we always
> want to clear them both, and we'll only have one set and not the other
> if one of the mode bits was set and not the other.
>
> But...I'm starting to wonder if we really need two flags for this. Would
> be be better served with a single ATTR_KILL_SUID_SGID flag? I wonder if
> that would simplify some of the logic in the whole setuid clearing
> morass.
Yeah, that would be a nice little cleanup.
Thanks,
Miklos
---
From: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Subject: 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 a09f99eddef4 ("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@xxxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Fixes: a09f99eddef4 ("fuse: fix killing s[ug]id in setattr")
Cc: <stable@xxxxxxxxxxxxxxx>
---
fs/fuse/dir.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1739,8 +1739,6 @@ static int fuse_setattr(struct dentry *e
* 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 *e
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;
}
--
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