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From: Serge Hallyn on 16 Feb 2010 17:50
From: Serge E. Hallyn <serue(a)us.ibm.com>

fsuid should always trail euid changes. So p9auth should
set fsuid as well when it sets ruid and euid. Whether the
suid should also be set is an open question - keeping the
old uid in suid may be useful, or may just serve to trick
lazy userspace.

Note that so long as we do not also set suid, the setuid_fixup()
code will not (when we later switch to setresuid()) fully
fill/clear capability sets. So while I had previously thought
that keeping suid unchanged would be useful, I think it is
better to change all uids.

Signed-off-by: Serge E. Hallyn <serue(a)us.ibm.com>
Cc: Greg KH <greg(a)kroah.com>
cc: rsc(a)swtch.com
Cc: Ashwin Ganti <ashwin.ganti(a)gmail.com>
Cc: ericvh(a)gmail.com
Cc: devel(a)linuxdriverproject.org
Cc: linux-kernel(a)vger.kernel.org
Cc: Ron Minnich <rminnich(a)gmail.com>
---
drivers/staging/p9auth/p9auth.c | 14 +++++++++-----
1 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/staging/p9auth/p9auth.c b/drivers/staging/p9auth/p9auth.c
index db79626..70ef45b 100644
--- a/drivers/staging/p9auth/p9auth.c
+++ b/drivers/staging/p9auth/p9auth.c
@@ -275,10 +275,14 @@ static ssize_t cap_write(struct file *filp, const char __user *buf,
goto out;
}
/*
- * What all id's need to be changed here? uid,
- * euid, fsid, savedids ?? Currently I am
- * changing the effective user id since most of
- * the authorisation decisions are based on it
+ * Change all uids. It might be useful to
+ * keep suid unchanged, however that will
+ * mean that changing from uid=0 to uid=!0
+ * pP is not emptied (only pE is), and when
+ * changing from uid=!0 to uid=0, sets are
+ * not filled. They will be correct after
+ * the next exec, but this is IMO not
+ * sufficient. So change all uids.
*/
new = prepare_creds();
if (!new) {
@@ -286,7 +290,7 @@ static ssize_t cap_write(struct file *filp, const char __user *buf,
goto out;
}
new->uid = (uid_t) target_int;
- new->euid = (uid_t) target_int;
+ new->suid = new->fsuid = new->euid = new->uid;
retval = commit_creds(new);
if (retval)
goto out;
--
1.6.1

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