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From: David Howells <dhowells@redhat.com>
To: Paul Moore <paul@paul-moore.com>
Cc: dhowells@redhat.com, keyrings@vger.kernel.org,
	selinux@vger.kernel.org, linux-security-module@vger.kernel.org
Subject: Re: Problem with 9ba09998baa9 ("selinux: Implement the watch_key security hook") in linux-next
Date: Tue, 21 Apr 2020 13:29:46 +0100
Message-ID: <2136640.1587472186@warthog.procyon.org.uk> (raw)
In-Reply-To: <CAHC9VhT95GJKNTMvTtmZL35UOoVwbGH-eDWZyELb5oZ5rQU+Tw@mail.gmail.com>

Paul Moore <paul@paul-moore.com> wrote:

> ... in particular it is the fifth argument to avc_has_perm(),
> "KEY_NEED_VIEW" which is a problem.  KEY_NEED_VIEW is not a SELinux
> permission and would likely result in odd behavior when passed to
> avc_has_perm().

I think it works because KEY_NEED_VIEW happens to coincide with KEY__VIEW.  It
should just use KEY__VIEW instead.

> it probably makes the most sense to pull the permission mapping in
> selinux_key_permission() out into a separate function, e.g.
> key_perm_to_av(...)

Agreed.  How about the attached patch?  I wonder if I should do bit-by-bit
translation rather than using a switch?  But then it's difficult to decide
what it means if someone passes in two KEY_NEED_* flags OR'd together - is it
either or both?

> and then use this newly created mapping function in [...]
> selinux_watch_key()

No, I think I should just hard-code KEY__VIEW there.

David
---
commit 70d1d82aa014ae4511976b4d80c17138006dddec
Author: David Howells <dhowells@redhat.com>
Date:   Tue Apr 21 13:15:16 2020 +0100

    selinux: Fix use of KEY_NEED_* instead of KEY__* perms
    
    selinux_key_getsecurity() is passing the KEY_NEED_* permissions to
    security_sid_to_context() instead of the KEY__* values.  It happens to work
    because the values are all coincident.
    
    Fixes: d720024e94de ("[PATCH] selinux: add hooks for key subsystem")
    Reported-by: Paul Moore <paul@paul-moore.com>
    Signed-off-by: David Howells <dhowells@redhat.com>

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 0b4e32161b77..32f7fa538c5f 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -6539,12 +6539,27 @@ static void selinux_key_free(struct key *k)
 	kfree(ksec);
 }
 
+static unsigned int selinux_keyperm_to_av(unsigned int need_perm)
+{
+	switch (need_perm) {
+	case KEY_NEED_VIEW:	return KEY__VIEW;
+	case KEY_NEED_READ:	return KEY__READ;
+	case KEY_NEED_WRITE:	return KEY__WRITE;
+	case KEY_NEED_SEARCH:	return KEY__SEARCH;
+	case KEY_NEED_LINK:	return KEY__LINK;
+	case KEY_NEED_SETATTR:	return KEY__SETATTR;
+	default:
+		return 0;
+	}
+}
+
 static int selinux_key_permission(key_ref_t key_ref,
 				  const struct cred *cred,
-				  unsigned perm)
+				  unsigned need_perm)
 {
 	struct key *key;
 	struct key_security_struct *ksec;
+	unsigned int perm;
 	u32 sid;
 
 	/* if no specific permissions are requested, we skip the
@@ -6553,6 +6568,7 @@ static int selinux_key_permission(key_ref_t key_ref,
 	if (perm == 0)
 		return 0;
 
+	perm = selinux_keyperm_to_av(need_perm);
 	sid = cred_sid(cred);
 
 	key = key_ref_to_ptr(key_ref);


  parent reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-17 15:48 Paul Moore
2020-04-17 16:32 ` Richard Haines
2020-04-17 16:59   ` Paul Moore
2020-04-21 12:29 ` David Howells [this message]
2020-04-22 19:20   ` Paul Moore
2020-04-22 21:09     ` Paul Moore
2020-04-24 23:43   ` David Howells
2020-04-26 20:53     ` Paul Moore
2020-04-27 14:12     ` [PATCH] selinux: Fix use of KEY_NEED_* instead of KEY__* perms David Howells
2020-04-27 14:36       ` Stephen Smalley
2020-04-27 15:24         ` Paul Moore
2020-04-27 17:02       ` Stephen Smalley
2020-04-27 22:17         ` Paul Moore
2020-04-28 12:54 ` [PATCH] selinux: Fix use of KEY_NEED_* instead of KEY__* perms [v2] David Howells
2020-04-28 14:32   ` Stephen Smalley
2020-04-28 15:57   ` David Howells
2020-04-28 16:19     ` Stephen Smalley
2020-05-01 16:37       ` Paul Moore
2020-05-12 22:33       ` [PATCH] keys: Make the KEY_NEED_* perms an enum rather than a mask David Howells
2020-05-13  1:04         ` Paul Moore
2020-05-13 12:58         ` Stephen Smalley
2020-05-13 15:25         ` Casey Schaufler
2020-05-13 23:13         ` David Howells
2020-05-14 12:08           ` Stephen Smalley
2020-05-14 14:45             ` Stephen Smalley
2020-05-13 23:16         ` David Howells
2020-05-13 23:25         ` David Howells
2020-05-14 11:00         ` Jarkko Sakkinen
2020-05-14 16:58         ` [PATCH] keys: Move permissions checking decisions into the checking code David Howells
2020-05-14 17:06           ` Casey Schaufler
2020-05-15 15:06           ` Stephen Smalley
2020-05-15 16:45           ` David Howells
2020-05-15 18:55             ` Stephen Smalley
2020-05-15 19:10               ` Casey Schaufler
2020-05-15 22:27             ` David Howells

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