linux-kernel - Re: 6.18.0-rc1: LTP syscalls ioctl_pidfd05: TFAIL: ioctl(pidfd, PIDFD_GET_INFO_SHORT, info

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Message-ID: <aPIPGeWo8gtxVxQX@yuki.lan>
Date: Fri, 17 Oct 2025 11:40:41 +0200
From: Cyril Hrubis <chrubis@...e.cz>
To: Naresh Kamboju <naresh.kamboju@...aro.org>
Cc: open list <linux-kernel@...r.kernel.org>, linux-fsdevel@...r.kernel.org,
	lkft-triage@...ts.linaro.org,
	Linux Regressions <regressions@...ts.linux.dev>,
	LTP List <ltp@...ts.linux.it>,
	Andrey Albershteyn <aalbersh@...nel.org>, Jan Kara <jack@...e.cz>,
	Arnd Bergmann <arnd@...db.de>,
	Christian Brauner <brauner@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Anders Roxell <anders.roxell@...aro.org>,
	Ben Copeland <benjamin.copeland@...aro.org>,
	Petr Vorel <pvorel@...e.cz>,
	Andrea Cervesato <andrea.cervesato@...e.com>
Subject: Re: 6.18.0-rc1: LTP syscalls ioctl_pidfd05: TFAIL: ioctl(pidfd,
 PIDFD_GET_INFO_SHORT, info_invalid) expected EINVAL: ENOTTY (25)

Hi!
> > ## Test error log
> > tst_buffers.c:57: TINFO: Test is using guarded buffers
> > tst_test.c:2021: TINFO: LTP version: 20250930
> > tst_test.c:2024: TINFO: Tested kernel: 6.18.0-rc1 #1 SMP PREEMPT
> > @1760657272 aarch64
> > tst_kconfig.c:88: TINFO: Parsing kernel config '/proc/config.gz'
> > tst_kconfig.c:676: TINFO: CONFIG_TRACE_IRQFLAGS kernel option detected
> > which might slow the execution
> > tst_test.c:1842: TINFO: Overall timeout per run is 0h 21m 36s
> > ioctl_pidfd05.c:45: TPASS: ioctl(pidfd, PIDFD_GET_INFO, NULL) : EINVAL (22)
> > ioctl_pidfd05.c:46: TFAIL: ioctl(pidfd, PIDFD_GET_INFO_SHORT,
> > info_invalid) expected EINVAL: ENOTTY (25)

Looking closely this is a different problem.

What we do in the test is that we pass PIDFD_IOCTL_INFO whith invalid
size with:

struct pidfd_info_invalid {
        uint32_t dummy;
};

#define PIDFD_GET_INFO_SHORT _IOWR(PIDFS_IOCTL_MAGIC, 11, struct pidfd_info_invalid)


And we expect to hit:

        if (usize < PIDFD_INFO_SIZE_VER0)
                return -EINVAL; /* First version, no smaller struct possible */

in fs/pidfs.c


And apparently the return value was changed in:

commit 3c17001b21b9f168c957ced9384abe969019b609
Author: Christian Brauner <brauner@...nel.org>
Date:   Fri Sep 12 13:52:24 2025 +0200

    pidfs: validate extensible ioctls
    
    Validate extensible ioctls stricter than we do now.
    
    Reviewed-by: Aleksa Sarai <cyphar@...har.com>
    Reviewed-by: Jan Kara <jack@...e.cz>
    Signed-off-by: Christian Brauner <brauner@...nel.org>

diff --git a/fs/pidfs.c b/fs/pidfs.c
index edc35522d75c..0a5083b9cce5 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -440,7 +440,7 @@ static bool pidfs_ioctl_valid(unsigned int cmd)
                 * erronously mistook the file descriptor for a pidfd.
                 * This is not perfect but will catch most cases.
                 */
-               return (_IOC_TYPE(cmd) == _IOC_TYPE(PIDFD_GET_INFO));
+               return extensible_ioctl_valid(cmd, PIDFD_GET_INFO, PIDFD_INFO_SIZE_VER0);
        }
 
        return false;


So kernel has changed error it returns, if this is a regression or not
is for kernel developers to decide.

-- 
Cyril Hrubis
chrubis@...e.cz