Re: [PATCH] watchdog: avoid usage of iterator after loop

From: Guenter Roeck
Date: Wed Mar 01 2023 - 13:31:47 EST


On 3/1/23 09:17, Jakob Koschel wrote:
If potentially no valid element is found, 'p' would contain an invalid
pointer past the iterator loop. To ensure 'p' is valid under any
circumstances, the kfree() should be within the loop body.

Additionally, Linus proposed to avoid any use of the list iterator
variable after the loop, in the attempt to move the list iterator
variable declaration into the marcro to avoid any potential misuse after

macro

the loop [1].

Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@xxxxxxxxxxxxxx/ [1]
Signed-off-by: Jakob Koschel <jkl820.git@xxxxxxxxx>
---
drivers/watchdog/watchdog_pretimeout.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/watchdog/watchdog_pretimeout.c b/drivers/watchdog/watchdog_pretimeout.c
index 376a495ab80c..d8c78696eaf5 100644
--- a/drivers/watchdog/watchdog_pretimeout.c
+++ b/drivers/watchdog/watchdog_pretimeout.c
@@ -207,10 +207,10 @@ void watchdog_unregister_pretimeout(struct watchdog_device *wdd)
list_for_each_entry_safe(p, t, &pretimeout_list, entry) {
if (p->wdd == wdd) {
list_del(&p->entry);
- break;
+ spin_unlock_irq(&pretimeout_lock);
+ kfree(p);
+ return;

Please just make it
kfree(p);
break;

There is no need to drop the spinlock here and/or to return
directly.

Thanks,
Guenter

}
}
spin_unlock_irq(&pretimeout_lock);
-
- kfree(p);
}

---
base-commit: c0927a7a5391f7d8e593e5e50ead7505a23cadf9
change-id: 20230301-watchdog-avoid-iter-after-loop-a197bf201435

Best regards,