proc: use strnlen() for name validation in __proc_create

Replace strlen(fn) with strnlen(fn, NAME_MAX + 1) when validating the
final path component in __proc_create().

This preserves the existing name limit while bounding the length scan to
one byte past the maximum name length.  Handle empty names separately, and
treat names longer than NAME_MAX as too long.

Link: https://lore.kernel.org/20260421122648.56723-2-thorsten.blum@linux.dev
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Thorsten Blum <thorsten.blum@linux.dev>
Cc: wangzijie <wangzijie1@honor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 8bb81e58c9d8c8a10831ad5644f8bfb9d752a097..3063080f3bb2a40bf4719323a9be7b07bda47bd7 100644 (file)
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -427,9 +427,13 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
        if (xlate_proc_name(name, parent, &fn) != 0)
                goto out;
        qstr.name = fn;
-       qstr.len = strlen(fn);
-       if (qstr.len == 0 || qstr.len >= 256) {
-               WARN(1, "name len %u\n", qstr.len);
+       qstr.len = strnlen(fn, NAME_MAX + 1);
+       if (qstr.len == 0) {
+               WARN(1, "empty name\n");
+               return NULL;
+       }
+       if (qstr.len > NAME_MAX) {
+               WARN(1, "name too long\n");
                return NULL;
        }
        if (qstr.len == 1 && fn[0] == '.') {