coredump: don't pointlessly check and spew warnings

When a write happens it doesn't make sense to check perform checks on
the input. Skip them.

Whether a fixes tag is licensed is a bit of a gray area here but I'll
add one for the socket validation part I added recently.

Link: https://lore.kernel.org/20250821-moosbedeckt-denunziant-7908663f3563@brauner
Fixes: 16195d2 ("coredump: validate socket name as it is written")
Reported-by: Brad Spengler <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

Author: brauner

fs/coredump.c

@@ -1466,11 +1466,15 @@ static int proc_dostring_coredump(const struct ctl_table *table, int write,
 	ssize_t retval;
 	char old_core_pattern[CORENAME_MAX_SIZE];
 
+	if (write)
+		return proc_dostring(table, write, buffer, lenp, ppos);
+
 	retval = strscpy(old_core_pattern, core_pattern, CORENAME_MAX_SIZE);
 
 	error = proc_dostring(table, write, buffer, lenp, ppos);
 	if (error)
 		return error;
+
 	if (!check_coredump_socket()) {
 		strscpy(core_pattern, old_core_pattern, retval + 1);
 		return -EINVAL;

fs/exec.c

@@ -2048,7 +2048,7 @@ static int proc_dointvec_minmax_coredump(const struct ctl_table *table, int writ
 {
 	int error = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 
-	if (!error)
+	if (!error && !write)
 		validate_coredump_safety();
 	return error;
 }