[PATCH bpf v2 1/2] bpf: Fix iter/task tid filtering

[PATCH bpf v2 1/2] bpf: Fix iter/task tid filtering

[Jordan Rome]

In userspace, you can add a tid filter by setting
the "task.tid" field for "bpf_iter_link_info".
However, `get_pid_task` when called for the
`BPF_TASK_ITER_TID` type should have been using
`PIDTYPE_PID` (tid) instead of `PIDTYPE_TGID` (pid).

Fixes: f0d74c4da1f0 ("bpf: Parameterize task iterators.")
Signed-off-by: Jordan Rome <linux@jordanrome.com>
---
 kernel/bpf/task_iter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 02aa9db8d796..5af9e130e500 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -99,7 +99,7 @@ static struct task_struct *task_seq_get_next(struct bpf_iter_seq_task_common *co
 		rcu_read_lock();
 		pid = find_pid_ns(common->pid, common->ns);
 		if (pid) {
-			task = get_pid_task(pid, PIDTYPE_TGID);
+			task = get_pid_task(pid, PIDTYPE_PID);
 			*tid = common->pid;
 		}
 		rcu_read_unlock();
--
2.43.5

[PATCH bpf v2 2/2] bpf: properly test iter/task tid filtering

[Jordan Rome]

Previously test_task_tid was setting `linfo.task.tid`
to `getpid()` which is the same as `gettid()` for the
parent process. Instead create a new child thread
and set `linfo.task.tid` to `gettid()` to make sure
the tid filtering logic is working as expected.

Signed-off-by: Jordan Rome <linux@jordanrome.com>
---
 .../selftests/bpf/prog_tests/bpf_iter.c       | 27 +++++++++++++++----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index 52e6f7570475..f0a3a9c18e9e 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
@@ -226,7 +226,7 @@ static void test_task_common_nocheck(struct bpf_iter_attach_opts *opts,
 	ASSERT_OK(pthread_create(&thread_id, NULL, &do_nothing_wait, NULL),
 		  "pthread_create");

-	skel->bss->tid = getpid();
+	skel->bss->tid = gettid();

 	do_dummy_read_opts(skel->progs.dump_task, opts);

@@ -249,25 +249,42 @@ static void test_task_common(struct bpf_iter_attach_opts *opts, int num_unknown,
 	ASSERT_EQ(num_known_tid, num_known, "check_num_known_tid");
 }

-static void test_task_tid(void)
+static void *run_test_task_tid(void *arg)
 {
 	LIBBPF_OPTS(bpf_iter_attach_opts, opts);
 	union bpf_iter_link_info linfo;
 	int num_unknown_tid, num_known_tid;

+	ASSERT_NEQ(getpid(), gettid(), "check_new_thread_id");
+
 	memset(&linfo, 0, sizeof(linfo));
-	linfo.task.tid = getpid();
+	linfo.task.tid = gettid();
 	opts.link_info = &linfo;
 	opts.link_info_len = sizeof(linfo);
 	test_task_common(&opts, 0, 1);

 	linfo.task.tid = 0;
 	linfo.task.pid = getpid();
-	test_task_common(&opts, 1, 1);
+	/* This includes the parent thread, this thread,
+	 * and the do_nothing_wait thread
+	 */
+	test_task_common(&opts, 2, 1);

 	test_task_common_nocheck(NULL, &num_unknown_tid, &num_known_tid);
-	ASSERT_GT(num_unknown_tid, 1, "check_num_unknown_tid");
+	ASSERT_GT(num_unknown_tid, 2, "check_num_unknown_tid");
 	ASSERT_EQ(num_known_tid, 1, "check_num_known_tid");
+
+	return NULL;
+}
+
+static void test_task_tid(void)
+{
+	pthread_t thread_id;
+
+	/* Create a new thread so pid and tid aren't the same */
+	ASSERT_OK(pthread_create(&thread_id, NULL, &run_test_task_tid, NULL),
+		  "pthread_create");
+	ASSERT_FALSE(pthread_join(thread_id, NULL), "pthread_join");
 }

 static void test_task_pid(void)
--
2.43.5

Re: [PATCH bpf v2 1/2] bpf: Fix iter/task tid filtering

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Wed, 16 Oct 2024 14:00:47 -0700 you wrote:
> In userspace, you can add a tid filter by setting
> the "task.tid" field for "bpf_iter_link_info".
> However, `get_pid_task` when called for the
> `BPF_TASK_ITER_TID` type should have been using
> `PIDTYPE_PID` (tid) instead of `PIDTYPE_TGID` (pid).
> 
> Fixes: f0d74c4da1f0 ("bpf: Parameterize task iterators.")
> Signed-off-by: Jordan Rome <linux@jordanrome.com>
> 
> [...]

Here is the summary with links:
  - [bpf,v2,1/2] bpf: Fix iter/task tid filtering
    https://git.kernel.org/bpf/bpf/c/9495a5b731fc
  - [bpf,v2,2/2] bpf: properly test iter/task tid filtering
    https://git.kernel.org/bpf/bpf/c/ee8c7c6c3f8c

You are awesome, thank you!
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