On Mon, 15 Nov 2021 11:08:17 +0300 Dan Carpenter wrote:
@Dan, is there a smatch checker for straigthforward use after free bugs? Like acessing pointer after free was called? I think, adding free_netdev() to check list might be good idea
I've skimmed througth smatch source and didn't find one, so can you, please, point out to it if it exists.
It's check_free_strict.c.
It does cross function analysis but free_netdev() is tricky because it doesn't free directly, it just drops the reference count. Also it delays freeing in the NETREG_UNREGISTERING path so this check might cause false positives?
I'd ignore that path, it's just special casing that's supposed to keep the driver-visible API sane. Nobody should be touching netdev past free_netdev(). Actually if you can it'd be interesting to add checks for using whatever netdev_priv(ndev) returned past free_netdev(ndev).
Most UAFs that come to mind from the past were people doing something like:
struct my_priv *mine = netdev_priv(ndev);
netdev_unregister(ndev); free_netdev(ndev);
free(mine->bla); /* UAF, free_netdev() frees the priv */
I'll add free_netdev() to the list of free functions and test it overnight tonight.
register_free_hook("free_netdev", &match_free, 0);