[LTP] [PATCH v2] Correctly check if PIDFD_INFO_EXIT is available

[LTP] [PATCH v2] Correctly check if PIDFD_INFO_EXIT is available

[Andrea Cervesato]

From: Andrea Cervesato <andrea.cervesato@suse.com>

When systems are not having the PIDFD_INFO_EXIT implementation,
ioctl_pidfd testing suite might fail with:

	ioctl_pidfd.h:32: TBROK: ioctl(...) failed: ENOTTY (25)

Fix the ioctl_pidfd_info_exit_supported() behavior, considering ENOTTY
error like a sign for not having PIDFD_INFO_EXIT implemented in the
system.

Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
Changes in v2:
- close pidfd when PIDFD_INFO_EXIT is supported
- Link to v1: https://lore.kernel.org/r/20250729-ioctl_pidfd_supported-v1-1-985626a0c46b@suse.com
---
 testcases/kernel/syscalls/ioctl/ioctl_pidfd.h | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/testcases/kernel/syscalls/ioctl/ioctl_pidfd.h b/testcases/kernel/syscalls/ioctl/ioctl_pidfd.h
index 8249ac753cf7fb8a3b749d55c7f0c3b30482c114..72ed3c8ae21bfa462ac76aaa865f5c71ce921e9a 100644
--- a/testcases/kernel/syscalls/ioctl/ioctl_pidfd.h
+++ b/testcases/kernel/syscalls/ioctl/ioctl_pidfd.h
@@ -11,9 +11,10 @@
 
 static inline int ioctl_pidfd_info_exit_supported(void)
 {
-	int ret = 0;
+	int ret;
 	pid_t pid;
 	int pidfd;
+	int supported = 0;
 	struct pidfd_info info;
 
 	if (tst_kvercmp(6, 15, 0) >= 0)
@@ -29,13 +30,18 @@ static inline int ioctl_pidfd_info_exit_supported(void)
 	pidfd = SAFE_PIDFD_OPEN(pid, 0);
 	SAFE_WAITPID(pid, NULL, 0);
 
-	SAFE_IOCTL(pidfd, PIDFD_GET_INFO, &info);
-	SAFE_CLOSE(pidfd);
+	ret = ioctl(pidfd, PIDFD_GET_INFO, &info);
+	if (ret == -1) {
+		if (errno != ENOTTY)
+			tst_brk(TBROK | TERRNO, "ioctl error");
+	} else {
+		if (info.mask & PIDFD_INFO_EXIT)
+			supported = 1;
+	}
 
-	if (info.mask & PIDFD_INFO_EXIT)
-		ret = 1;
+	SAFE_CLOSE(pidfd);
 
-	return ret;
+	return supported;
 }
 
 #endif

---
base-commit: 91e6272febf95e19a8300695dfc2089569adf9d8
change-id: 20250729-ioctl_pidfd_supported-437d25a4c382

Best regards,
-- 
Andrea Cervesato <andrea.cervesato@suse.com>


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Re: [LTP] [PATCH v2] Correctly check if PIDFD_INFO_EXIT is available

[Cyril Hrubis]

Hi!
Reviewed-by: Cyril Hrubis <chrubis@suse.cz>

-- 
Cyril Hrubis
chrubis@suse.cz

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Re: [LTP] [PATCH v2] Correctly check if PIDFD_INFO_EXIT is available

[Andrea Cervesato via ltp]

On 7/30/25 11:35 AM, Cyril Hrubis wrote:
> Hi!
> Reviewed-by: Cyril Hrubis <chrubis@suse.cz>
>
It seems we need to add also a couple of errno checks more. 
ioctl(PIDFD_INFO_EXIT ...) starts to fail with EINVAL from a certain 
version of the kernel, after introducing `pidfd_ioctl` function in 
fs/pidfs.c, while before only ENOTTY was raised.

After the introduction of "cdda1f26e74b - pidfd: add ioctl to retrieve 
pid info" in v6.13, the logic inside the kernel changed and we get ESRCH 
error due to the introduction of `struct pidfd_info`, but the lack of 
PIDFD_INFO_EXIT support: at that specific commit, only PIDFD_INFO_PID is 
supported.

This is due to the implementation of `pidfd_ioctl()`, that is not 
validating commands before asking for a pid task.

I guess there's either a enhancement to do in the kernel implementation, 
or a lack of checks from our side. Since we are talking about 3 versions 
of the kernel ago, we should probably verify that kernel doesn't support 
PIDFD_INFO_EXIT by looking at the following ioctl() errno:

- ENOTTY
- EINVAL
- ESRCH

- Andrea


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Re: [LTP] [PATCH v2] Correctly check if PIDFD_INFO_EXIT is available

[Andrea Cervesato via ltp]

On 7/30/25 2:04 PM, Andrea Cervesato wrote:
> On 7/30/25 11:35 AM, Cyril Hrubis wrote:
>> Hi!
>> Reviewed-by: Cyril Hrubis <chrubis@suse.cz>
>>
> It seems we need to add also a couple of errno checks more. 
> ioctl(PIDFD_INFO_EXIT ...) starts to fail with EINVAL from a certain 
> version of the kernel, after introducing `pidfd_ioctl` function in 
> fs/pidfs.c, while before only ENOTTY was raised.
>
> After the introduction of "cdda1f26e74b - pidfd: add ioctl to retrieve 
> pid info" in v6.13, the logic inside the kernel changed and we get 
> ESRCH error due to the introduction of `struct pidfd_info`, but the 
> lack of PIDFD_INFO_EXIT support: at that specific commit, only 
> PIDFD_INFO_PID is supported.
>
> This is due to the implementation of `pidfd_ioctl()`, that is not 
> validating commands before asking for a pid task.
>
> I guess there's either a enhancement to do in the kernel 
> implementation, or a lack of checks from our side. Since we are 
> talking about 3 versions of the kernel ago, we should probably verify 
> that kernel doesn't support PIDFD_INFO_EXIT by looking at the 
> following ioctl() errno:
>
> - ENOTTY
> - EINVAL
> - ESRCH
>
> - Andrea
>
The `pidfd_ioctl()` commands check has been introduced in v6.13 with 
"8ce352818820 pidfs: check for valid ioctl commands", so the patch v4 
that I sent needs to check for ENOIOCTLCMD as well..

- Andrea


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