linux-kernel - [PATCH] exec: remove redundant save asides of old pid/vpid

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Message-ID: <20250201083127.GA1185473@lichtman.org>
Date: Sat, 1 Feb 2025 08:31:27 +0000
From: Nir Lichtman <nir@...htman.org>
To: viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz,
	kees@...nel.org, ebiederm@...ssion.com,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] exec: remove redundant save asides of old pid/vpid

Problem: Old pid and vpid are redundantly saved aside before starting to
parse the binary, with the comment claiming that it is required since
load_binary changes it, though from inspection in the source,
load_binary does not change the pid and this wouldn't make sense since
execve does not create any new process, quote from man page of execve:
"there is no new process; many attributes of the calling process remain
unchanged (in particular, its PID)."

Solution: Remove the saving aside of both and later on use them directly
from the current object, instead of via the saved aside objects.

Signed-off-by: Nir Lichtman <nir@...htman.org>
---

Side-note: Tested this solution with a defconfig x86_64 and an initramfs
with Busybox and confirmed to work fine.

 fs/exec.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 506cd411f4ac..6bb0a7b15f7e 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1789,15 +1789,8 @@ static int search_binary_handler(struct linux_binprm *bprm)
 /* binfmt handlers will call back into begin_new_exec() on success. */
 static int exec_binprm(struct linux_binprm *bprm)
 {
-	pid_t old_pid, old_vpid;
 	int ret, depth;
 
-	/* Need to fetch pid before load_binary changes it */
-	old_pid = current->pid;
-	rcu_read_lock();
-	old_vpid = task_pid_nr_ns(current, task_active_pid_ns(current->parent));
-	rcu_read_unlock();
-
 	/* This allows 4 levels of binfmt rewrites before failing hard. */
 	for (depth = 0;; depth++) {
 		struct file *exec;
@@ -1826,8 +1819,9 @@ static int exec_binprm(struct linux_binprm *bprm)
 	}
 
 	audit_bprm(bprm);
-	trace_sched_process_exec(current, old_pid, bprm);
-	ptrace_event(PTRACE_EVENT_EXEC, old_vpid);
+	trace_sched_process_exec(current, current->pid, bprm);
+	ptrace_event(PTRACE_EVENT_EXEC,
+			task_pid_nr_ns(current, task_active_pid_ns(current->parent)));
 	proc_exec_connector(current);
 	return 0;
 }
-- 
2.39.5