From bef2b32a149030babba8ad5d2b6c121638fb911d Mon Sep 17 00:00:00 2001
From: Paul Moore <paul@paul-moore.com>
Date: Thu, 23 Sep 2021 09:50:11 -0400
Subject: [PATCH] selinux,smack: fix subjective/objective credential use mixups
Git-commit: a3727a8bac0a9e77c70820655fd8715523ba3db7
Patch-mainline: v5.15-rc3
References: CVE-2021-43057 bsc#1192260 stable-5.14.8

commit a3727a8bac0a9e77c70820655fd8715523ba3db7 upstream.

Jann Horn reported a problem with commit eb1231f73c4d ("selinux:
clarify task subjective and objective credentials") where some LSM
hooks were attempting to access the subjective credentials of a task
other than the current task.  Generally speaking, it is not safe to
access another task's subjective credentials and doing so can cause
a number of problems.

Further, while looking into the problem, I realized that Smack was
suffering from a similar problem brought about by a similar commit
1fb057dcde11 ("smack: differentiate between subjective and objective
task credentials").

This patch addresses this problem by restoring the use of the task's
objective credentials in those cases where the task is other than the
current executing task.  Not only does this resolve the problem
reported by Jann, it is arguably the correct thing to do in these
cases.

Cc: stable@vger.kernel.org
Fixes: eb1231f73c4d ("selinux: clarify task subjective and objective credentials")
Fixes: 1fb057dcde11 ("smack: differentiate between subjective and objective task credentials")
Reported-by: Jann Horn <jannh@google.com>
Acked-by: Eric W. Biederman <ebiederm@xmission.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 security/selinux/hooks.c   | 4 ++--
 security/smack/smack_lsm.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index b0032c42333e..572e564bf6cd 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2155,7 +2155,7 @@ static int selinux_ptrace_access_check(struct task_struct *child,
 static int selinux_ptrace_traceme(struct task_struct *parent)
 {
 	return avc_has_perm(&selinux_state,
-			    task_sid_subj(parent), task_sid_obj(current),
+			    task_sid_obj(parent), task_sid_obj(current),
 			    SECCLASS_PROCESS, PROCESS__PTRACE, NULL);
 }
 
@@ -6218,7 +6218,7 @@ static int selinux_msg_queue_msgrcv(struct kern_ipc_perm *msq, struct msg_msg *m
 	struct ipc_security_struct *isec;
 	struct msg_security_struct *msec;
 	struct common_audit_data ad;
-	u32 sid = task_sid_subj(target);
+	u32 sid = task_sid_obj(target);
 	int rc;
 
 	isec = selinux_ipc(msq);
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 223a6da0e6dc..b1694fa6f12b 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -2016,7 +2016,7 @@ static int smk_curacc_on_task(struct task_struct *p, int access,
 				const char *caller)
 {
 	struct smk_audit_info ad;
-	struct smack_known *skp = smk_of_task_struct_subj(p);
+	struct smack_known *skp = smk_of_task_struct_obj(p);
 	int rc;
 
 	smk_ad_init(&ad, caller, LSM_AUDIT_DATA_TASK);
@@ -3480,7 +3480,7 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
  */
 static int smack_getprocattr(struct task_struct *p, char *name, char **value)
 {
-	struct smack_known *skp = smk_of_task_struct_subj(p);
+	struct smack_known *skp = smk_of_task_struct_obj(p);
 	char *cp;
 	int slen;
 
-- 
2.26.2