From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Luca Boccassi <luca.boccassi@gmail.com>,
	Christian Brauner <brauner@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.18 487/641] pidfs: return -EREMOTE when PIDFD_GET_INFO is called on another ns
Date: Tue, 24 Feb 2026 17:23:33 -0800
Message-ID: <20260225012400.318315877@linuxfoundation.org>
In-Reply-To: <20260225012348.915798704@linuxfoundation.org>
References: <20260225012348.915798704@linuxfoundation.org>
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6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Luca Boccassi <luca.boccassi@gmail.com>

[ Upstream commit ab89060fbc92edd6e852bf0f533f29140afabe0e ]

Currently it is not possible to distinguish between the case where a
process has already exited and the case where a process is in a
different namespace, as both return -ESRCH.
glibc's pidfd_getpid() procfs-based implementation returns -EREMOTE
in the latter, so that distinguishing the two is possible, as the
fdinfo in procfs will list '0' as the PID in that case:

https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/pidfd_getpid.c;h=860829cf07da2267484299ccb02861822c0d07b4;hb=HEAD#l121

Change the error code so that the kernel also returns -EREMOTE in
that case.

Fixes: 7477d7dce48a ("pidfs: allow to retrieve exit information")

Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
Link: https://patch.msgid.link/20260127225209.2293342-1-luca.boccassi@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/pidfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/pidfs.c b/fs/pidfs.c
index f4d7dac1b4494..34987fcdd9a87 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -321,7 +321,7 @@ static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg)
 	 * namespace hierarchy.
 	 */
 	if (!pid_in_current_pidns(pid))
-		return -ESRCH;
+		return -EREMOTE;
 
 	attr = READ_ONCE(pid->attr);
 	if (mask & PIDFD_INFO_EXIT) {
-- 
2.51.0