[PATCH 5.10.y] apparmor: use target task's context in apparmor_getprocattr()

[Sasha Levin <sashal@kernel.org>]

From: Cengiz Can <cengiz.can@canonical.com>

[ Upstream commit 4afc61702bdcc3b9b519749ef966cf762a6e7051 ]

apparmor_getprocattr() incorrectly calls task_ctx(current) instead of
task_ctx(task) when retrieving prev and exec attributes, returning the
caller's labels rather than the target's.

Fix by passing task to task_ctx().

The issue can be reproduced when a process with an onexec transition
(e.g., configured by a container runtime) is inspected via
/proc/<pid>/attr/apparmor/exec. The reader's own value is returned
instead of the target's.

Reported-by: Qualys Security Advisory <qsa@qualys.com>
Fixes: 3b529a7600d8 ("apparmor: move task domain change info to task security")
Cc: stable@vger.kernel.org
Co-developed-by: Cengiz Can <cengiz.can@canonical.com>
Signed-off-by: Cengiz Can <cengiz.can@canonical.com>
Co-developed-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 security/apparmor/lsm.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 37aa1650c74eb..c1c8efd7db8c3 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -589,25 +589,23 @@ static int apparmor_getprocattr(struct task_struct *task, char *name,
 				char **value)
 {
 	int error = -ENOENT;
-	/* released below */
-	const struct cred *cred = get_task_cred(task);
-	struct aa_task_ctx *ctx = task_ctx(current);
 	struct aa_label *label = NULL;
 
+	rcu_read_lock();
 	if (strcmp(name, "current") == 0)
-		label = aa_get_newest_label(cred_label(cred));
-	else if (strcmp(name, "prev") == 0  && ctx->previous)
-		label = aa_get_newest_label(ctx->previous);
-	else if (strcmp(name, "exec") == 0 && ctx->onexec)
-		label = aa_get_newest_label(ctx->onexec);
+		label = aa_get_newest_cred_label(__task_cred(task));
+	else if (strcmp(name, "prev") == 0  && task_ctx(task)->previous)
+		label = aa_get_newest_label(task_ctx(task)->previous);
+	else if (strcmp(name, "exec") == 0 && task_ctx(task)->onexec)
+		label = aa_get_newest_label(task_ctx(task)->onexec);
 	else
 		error = -EINVAL;
+	rcu_read_unlock();
 
 	if (label)
 		error = aa_getprocattr(label, value);
 
 	aa_put_label(label);
-	put_cred(cred);
 
 	return error;
 }
-- 
2.53.0