linux-kernel - [PATCH 1/8] p9auth: set fsuid

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Message-Id: <1266360301-30081-1-git-send-email-serue@us.ibm.com>
Date:	Tue, 16 Feb 2010 16:44:54 -0600
From:	Serge Hallyn <serue@...ibm.com>
To:	serue@...ibm.com
Cc:	Greg KH <greg@...ah.com>, rsc@...ch.com,
	Ashwin Ganti <ashwin.ganti@...il.com>, ericvh@...il.com,
	devel@...uxdriverproject.org, linux-kernel@...r.kernel.org,
	Ron Minnich <rminnich@...il.com>
Subject: [PATCH 1/8] p9auth: set fsuid

From: Serge E. Hallyn <serue@...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@...ibm.com>
Cc: Greg KH <greg@...ah.com>
cc: rsc@...ch.com
Cc: Ashwin Ganti <ashwin.ganti@...il.com>
Cc: ericvh@...il.com
Cc: devel@...uxdriverproject.org
Cc: linux-kernel@...r.kernel.org
Cc: Ron Minnich <rminnich@...il.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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