irq_cpu_rmap_release() calls cpu_rmap_put(), which may free the rmap.
So we need to clear the pointer to our glue structure in rmap before
doing that, not after.

Fixes: 4e0473f1060a ("lib: cpu_rmap: Avoid use after free on rmap->obj ...")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
I noticed this issue when reviewing stable changes.  I haven't tested
the change.

Ben.

 lib/cpu_rmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/cpu_rmap.c b/lib/cpu_rmap.c
index 73c1636b927b..4c348670da31 100644
--- a/lib/cpu_rmap.c
+++ b/lib/cpu_rmap.c
@@ -280,8 +280,8 @@ static void irq_cpu_rmap_release(struct kref *ref)
 	struct irq_glue *glue =
 		container_of(ref, struct irq_glue, notify.kref);
 
-	cpu_rmap_put(glue->rmap);
 	glue->rmap->obj[glue->index] = NULL;
+	cpu_rmap_put(glue->rmap);
 	kfree(glue);
 }
 

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Fri, 2 Jun 2023 20:28:15 +0200 you wrote:
> irq_cpu_rmap_release() calls cpu_rmap_put(), which may free the rmap.
> So we need to clear the pointer to our glue structure in rmap before
> doing that, not after.
> 
> Fixes: 4e0473f1060a ("lib: cpu_rmap: Avoid use after free on rmap->obj ...")
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
> 
> [...]

Here is the summary with links:
  - [net] lib: cpu_rmap: Fix potential use-after-free in irq_cpu_rmap_release()
    https://git.kernel.org/netdev/net/c/7c5d4801ecf0

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

Hi,

On Fri, 2023-06-02 at 20:28 +0200, Ben Hutchings wrote:
> irq_cpu_rmap_release() calls cpu_rmap_put(), which may free the rmap.
> So we need to clear the pointer to our glue structure in rmap before
> doing that, not after.
> 
> Fixes: 4e0473f1060a ("lib: cpu_rmap: Avoid use after free on rmap->obj ...")
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

The patch LGTM, but please include the full blamed commit title into
the fixes tag. A new version will be needed.

Also add Jacob and Saeed to the cc-list

Thanks,

Paolo

On Fri, Jun 02, 2023 at 08:28:15PM +0200, Ben Hutchings wrote:
> irq_cpu_rmap_release() calls cpu_rmap_put(), which may free the rmap.
> So we need to clear the pointer to our glue structure in rmap before
> doing that, not after.
> 
> Fixes: 4e0473f1060a ("lib: cpu_rmap: Avoid use after free on rmap->obj ...")
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

Reviewed-by: Simon Horman <simon.horman@corigine.com>