Re: [PATCH 3/3] binder: Handle start==NULL in binder_update_page_range()

[Christian Brauner]

On Fri Oct 18, 2019 at 10:56 PM Jann Horn wrote:
> The old loop wouldn't stop when reaching `start` if `start==NULL`, instead
> continuing backwards to index -1 and crashing.
> 
> Luckily you need to be highly privileged to map things at NULL, so it's not
> a big problem.
> 
> Fix it by adjusting the loop so that the loop variable is always in bounds.
> 
> This patch is deliberately minimal to simplify backporting, but IMO this
> function could use a refactor. The jump labels in the second loop body are
> horrible (the error gotos should be jumping to free_range instead), and
> both loops would look nicer if they just iterated upwards through indices.
> And the up_read()+mmput() shouldn't be duplicated like that.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 457b9a6f09f0 ("Staging: android: add binder driver")
> Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>

Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>