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From: Tejun Heo <tj@kernel.org>
To: torvalds@linuxfoundation.org, ebiederm@xmission.com,
	mkoutny@suse.com, axboe@kernel.dk, keescook@chromium.org,
	oleg@redhat.com, peterz@infradead.org, tglx@linutronix.de,
	jnewsome@torproject.org, legion@kernel.org, luto@amacapital.net,
	jannh@google.com
Cc: linux-kernel@vger.kernel.org, security@kernel.org,
	kernel-team@fb.com, Tejun Heo <tj@kernel.org>
Subject: [PATCH 5/6] selftests: cgroup: Test open-time credential usage for migration checks
Date: Thu,  9 Dec 2021 11:47:06 -1000	[thread overview]
Message-ID: <20211209214707.805617-6-tj@kernel.org> (raw)
In-Reply-To: <20211209214707.805617-1-tj@kernel.org>

When a task is writing to an fd opened by a different task, the perm check
should use the credentials of the latter task. Add a test for it.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 tools/testing/selftests/cgroup/test_core.c | 68 ++++++++++++++++++++++
 1 file changed, 68 insertions(+)

diff --git a/tools/testing/selftests/cgroup/test_core.c b/tools/testing/selftests/cgroup/test_core.c
index 3df648c37876..01b766506973 100644
--- a/tools/testing/selftests/cgroup/test_core.c
+++ b/tools/testing/selftests/cgroup/test_core.c
@@ -674,6 +674,73 @@ static int test_cgcore_thread_migration(const char *root)
 	return ret;
 }
 
+/*
+ * cgroup migration permission check should be performed based on the
+ * credentials at the time of open instead of write.
+ */
+static int test_cgcore_lesser_euid_open(const char *root)
+{
+	const uid_t test_euid = 65534;	/* usually nobody, any !root is fine */
+	int ret = KSFT_FAIL;
+	char *cg_test_a = NULL, *cg_test_b = NULL;
+	char *cg_test_a_procs = NULL, *cg_test_b_procs = NULL;
+	int cg_test_b_procs_fd = -1;
+	uid_t saved_uid;
+
+	cg_test_a = cg_name(root, "cg_test_a");
+	cg_test_b = cg_name(root, "cg_test_b");
+
+	if (!cg_test_a || !cg_test_b)
+		goto cleanup;
+
+	cg_test_a_procs = cg_name(cg_test_a, "cgroup.procs");
+	cg_test_b_procs = cg_name(cg_test_b, "cgroup.procs");
+
+	if (!cg_test_a_procs || !cg_test_b_procs)
+		goto cleanup;
+
+	if (cg_create(cg_test_a) || cg_create(cg_test_b))
+		goto cleanup;
+
+	if (cg_enter_current(cg_test_a))
+		goto cleanup;
+
+	if (chown(cg_test_a_procs, test_euid, -1) ||
+	    chown(cg_test_b_procs, test_euid, -1))
+		goto cleanup;
+
+	saved_uid = geteuid();
+	if (seteuid(test_euid))
+		goto cleanup;
+
+	cg_test_b_procs_fd = open(cg_test_b_procs, O_RDWR);
+
+	if (seteuid(saved_uid))
+		goto cleanup;
+
+	if (cg_test_b_procs_fd < 0)
+		goto cleanup;
+
+	if (write(cg_test_b_procs_fd, "0", 1) >= 0 || errno != EACCES)
+		goto cleanup;
+
+	ret = KSFT_PASS;
+
+cleanup:
+	cg_enter_current(root);
+	if (cg_test_b_procs_fd >= 0)
+		close(cg_test_b_procs_fd);
+	if (cg_test_b)
+		cg_destroy(cg_test_b);
+	if (cg_test_a)
+		cg_destroy(cg_test_a);
+	free(cg_test_b_procs);
+	free(cg_test_a_procs);
+	free(cg_test_b);
+	free(cg_test_a);
+	return ret;
+}
+
 #define T(x) { x, #x }
 struct corecg_test {
 	int (*fn)(const char *root);
@@ -689,6 +756,7 @@ struct corecg_test {
 	T(test_cgcore_proc_migration),
 	T(test_cgcore_thread_migration),
 	T(test_cgcore_destroy),
+	T(test_cgcore_lesser_euid_open),
 };
 #undef T
 
-- 
2.34.1


  parent reply	other threads:[~2021-12-09 21:47 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-09 21:47 [PATCHSET cgroup/for-5.16-fixes] cgroup: Use open-time creds and namespace for migration perm checks Tejun Heo
2021-12-09 21:47 ` [PATCH 1/6] cgroup: Use open-time credentials for process migraton " Tejun Heo
2021-12-10 17:41   ` Linus Torvalds
2021-12-09 21:47 ` [PATCH 2/6] cgroup: Allocate cgroup_file_ctx for kernfs_open_file->priv Tejun Heo
2021-12-10 17:53   ` Linus Torvalds
2021-12-10 18:38     ` Tejun Heo
2021-12-10 18:45       ` Linus Torvalds
2021-12-10 19:06         ` Tejun Heo
2021-12-10 19:14           ` Linus Torvalds
2021-12-09 21:47 ` [PATCH 3/6] cgroup: Use open-time cgroup namespace for process migration perm checks Tejun Heo
2021-12-09 21:47 ` [PATCH 4/6] selftests: cgroup: Make cg_create() use 0755 for permission instead of 0644 Tejun Heo
2021-12-09 21:47 ` Tejun Heo [this message]
2021-12-09 21:47 ` [PATCH 6/6] selftests: cgroup: Test open-time cgroup namespace usage for migration checks Tejun Heo
2021-12-13 19:18 [PATCHSET v2 cgroup/for-5.16-fixes] cgroup: Use open-time creds and namespace for migration perm checks Tejun Heo
2021-12-13 19:18 ` [PATCH 5/6] selftests: cgroup: Test open-time credential usage for migration checks Tejun Heo
2021-12-14 17:04   ` Michal Koutný

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