linux-kernel - [PATCH 1/2] efi: remove use of list iterator variable after loop

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Date:   Fri,  1 Apr 2022 00:10:29 +0200
From:   Jakob Koschel <jakobkoschel@...il.com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mike Rapoport <rppt@...nel.org>,
        "Brian Johannesmeyer" <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>, Jakob Koschel <jakobkoschel@...il.com>
Subject: [PATCH 1/2] efi: remove use of list iterator variable after loop

In preparation to limiting the scope of a list iterator to the list
traversal loop, use a dedicated pointer to iterate through the list [1].

In the current state the list_for_each_entry() is guaranteed to
hit a break or goto in order to work properly. If the list iterator
executes completely or the list is empty the iterator variable contains
a type confused bogus value infered from the head of the list.

With this patch the variable used past the list iterator is only set
if the list exists early and is NULL otherwise. It should therefore
be safe to just set *prev = NULL (as it was before).

Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/
Signed-off-by: Jakob Koschel <jakobkoschel@...il.com>
---
 drivers/firmware/efi/vars.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index cae590bd08f2..3994aad38661 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -1081,14 +1081,16 @@ int __efivar_entry_iter(int (*func)(struct efivar_entry *, void *),
 			struct list_head *head, void *data,
 			struct efivar_entry **prev)
 {
-	struct efivar_entry *entry, *n;
+	struct efivar_entry *entry = NULL, *iter, *n;
 	int err = 0;
 
 	if (!prev || !*prev) {
-		list_for_each_entry_safe(entry, n, head, list) {
-			err = func(entry, data);
-			if (err)
+		list_for_each_entry_safe(iter, n, head, list) {
+			err = func(iter, data);
+			if (err) {
+				entry = iter;
 				break;
+			}
 		}
 
 		if (prev)

base-commit: d888c83fcec75194a8a48ccd283953bdba7b2550
-- 
2.25.1