The following commit has been merged into the timers/urgent branch of tip:

Commit-ID:     d7ad05c86e2191bd66e5b62fca8da53c4a53484f
Gitweb:        https://git.kernel.org/tip/d7ad05c86e2191bd66e5b62fca8da53c4a53484f
Author:        Levi Yun <ppbuk5246@gmail.com>
AuthorDate:    Mon, 06 May 2024 05:10:59 +01:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Wed, 08 May 2024 11:19:43 +02:00

timers/migration: Prevent out of bounds access on failure

When tmigr_setup_groups() fails the level 0 group allocation, then the
cleanup derefences index -1 of the local stack array.

Prevent this by checking the loop condition first.

Fixes: 7ee988770326 ("timers: Implement the hierarchical pull model")
Signed-off-by: Levi Yun <ppbuk5246@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Link: https://lore.kernel.org/r/20240506041059.86877-1-ppbuk5246@gmail.com
---
 kernel/time/timer_migration.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c
index ccba875..8441311 100644
--- a/kernel/time/timer_migration.c
+++ b/kernel/time/timer_migration.c
@@ -1596,7 +1596,7 @@ static int tmigr_setup_groups(unsigned int cpu, unsigned int node)
 
 	} while (i < tmigr_hierarchy_levels);
 
-	do {
+	while (i > 0) {
 		group = stack[--i];
 
 		if (err < 0) {
@@ -1645,7 +1645,7 @@ static int tmigr_setup_groups(unsigned int cpu, unsigned int node)
 				tmigr_connect_child_parent(child, group);
 			}
 		}
-	} while (i > 0);
+	}
 
 	kfree(stack);

On Wed, May 08, 2024 at 09:45:41AM -0000, tip-bot2 for Levi Yun wrote:
> The following commit has been merged into the timers/urgent branch of tip:

(Yes, I noted above)

...

> -	do {
> +	while (i > 0) {
>  		group = stack[--i];

Looking at this and most used patterns for cleanup loops, I would amend
this to

	while (i--) {
		group = stack[i];

which seems to me an equivalent.

>  		if (err < 0) {
> @@ -1645,7 +1645,7 @@ static int tmigr_setup_groups(unsigned int cpu, unsigned int node)
>  				tmigr_connect_child_parent(child, group);
>  			}
>  		}
> -	} while (i > 0);
> +	}

-- 
With Best Regards,
Andy Shevchenko