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Merge patch series "pidfd: improve uapi when task isn't found"

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Christian Brauner <brauner@kernel.org> says:

We currently report EINVAL whenever a struct pid has no tasked attached
anymore thereby conflating two concepts:

(1) The task has already been reaped.
(2) The caller requested a pidfd for a thread-group leader but the pid
    actually references a struct pid that isn't used as a thread-group
    leader.

This is causing issues for non-threaded workloads as in [1] where they
expect ESRCH to be reported, not EINVAL. I think that's a very resonable
assumption.

This patch tries to allow userspace to distinguish between (1) and (2).
This is racy of course but that shouldn't matter.

* patches from https://lore.kernel.org/r/20250403-work-pidfd-fixes-v1-0-a123b6ed6716@kernel.org:
  selftest/pidfd: add test for thread-group leader pidfd open for thread
  pidfd: improve uapi when task isn't found
  pidfd: remove unneeded NULL check from pidfd_prepare()
  selftests/pidfd: adapt to recent changes

Link: https://lore.kernel.org/r/20250403-work-pidfd-fixes-v1-0-a123b6ed6716@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner
2025-04-04 16:06:55 +02:00
parent 0af2f6be1b 4fc3f73c16
commit 1e940fff94
2 changed files with 27 additions and 9 deletions
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23
kernel/fork.c
View File

@@ -2108,10 +2108,27 @@ static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **re
*/
int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret)
{
bool thread = flags & PIDFD_THREAD;
int err = 0;
if (!pid || !pid_has_task(pid, thread ? PIDTYPE_PID : PIDTYPE_TGID))
return -EINVAL;
if (!(flags & PIDFD_THREAD)) {
/*
* If this is struct pid isn't used as a thread-group
* leader pid but the caller requested to create a
* thread-group leader pidfd then report ENOENT to the
* caller as a hint.
*/
if (!pid_has_task(pid, PIDTYPE_TGID))
err = -ENOENT;
}
/*
* If this wasn't a thread-group leader struct pid or the task
* got reaped in the meantime report -ESRCH to userspace.
*/
if (!pid_has_task(pid, PIDTYPE_PID))
err = -ESRCH;
if (err)
return err;
return __pidfd_prepare(pid, flags, ret);
}

13
tools/testing/selftests/pidfd/pidfd_info_test.c
View File

@@ -299,6 +299,7 @@ TEST_F(pidfd_info, thread_group)
/* Opening a thread as a thread-group leader must fail. */
pidfd_thread = sys_pidfd_open(pid_thread, 0);
ASSERT_LT(pidfd_thread, 0);
ASSERT_EQ(errno, ENOENT);
/* Opening a thread as a PIDFD_THREAD must succeed. */
pidfd_thread = sys_pidfd_open(pid_thread, PIDFD_THREAD);
@@ -362,9 +363,9 @@ TEST_F(pidfd_info, thread_group)
ASSERT_EQ(ioctl(pidfd_leader, PIDFD_GET_INFO, &info), 0);
ASSERT_FALSE(!!(info.mask & PIDFD_INFO_CREDS));
ASSERT_TRUE(!!(info.mask & PIDFD_INFO_EXIT));
/* The thread-group leader exited successfully. Only the specific thread was SIGKILLed. */
ASSERT_TRUE(WIFEXITED(info.exit_code));
ASSERT_EQ(WEXITSTATUS(info.exit_code), 0);
/* Even though the thread-group exited successfully it will still report the group exit code. */
ASSERT_TRUE(WIFSIGNALED(info.exit_code));
ASSERT_EQ(WTERMSIG(info.exit_code), SIGKILL);
/*
* Retrieve exit information for the thread-group leader via the
@@ -375,9 +376,9 @@ TEST_F(pidfd_info, thread_group)
ASSERT_FALSE(!!(info2.mask & PIDFD_INFO_CREDS));
ASSERT_TRUE(!!(info2.mask & PIDFD_INFO_EXIT));
/* The thread-group leader exited successfully. Only the specific thread was SIGKILLed. */
ASSERT_TRUE(WIFEXITED(info2.exit_code));
ASSERT_EQ(WEXITSTATUS(info2.exit_code), 0);
/* Even though the thread-group exited successfully it will still report the group exit code. */
ASSERT_TRUE(WIFSIGNALED(info2.exit_code));
ASSERT_EQ(WTERMSIG(info2.exit_code), SIGKILL);
/* Retrieve exit information for the thread. */
info.mask = PIDFD_INFO_CGROUPID | PIDFD_INFO_EXIT;