Re: [PATCH] serial: sh-sci: Fix use-after-free on subsequent port startup

[Simon Horman]

On Tue, Jul 17, 2018 at 10:58:10AM +0200, Geert Uytterhoeven wrote:
> sci_request_irq() checks port->irqstr[j] for a NULL pointer, to decide
> if a fallback interrupt name string should be allocated or not.
> 
> While this string is freed during port shutdown, the pointer is not
> zeroed.  Hence on a subsequent startup of the port, it will still be
> pointing to the freed memory, leading to e.g.
> 
>     WARNING: CPU: 0 PID: 404 at fs/proc/generic.c:388 __proc_create+0xbc/0x260
>     name len 0
> 
> or to a crash (the latter is more likely with CONFIG_DEBUG_SLAB=y, due
> to the poisoning of freed memory).
> 
> Instead of zeroeing the pointer at multiple places, preinitialize
> port->irqstr[j] to zero to fix this.
> 
> Fixes: 8b0bbd956228ae87 ("serial: sh-sci: Add support for R7S9210")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

Reviewed-by: Simon Horman <horms+renesas@xxxxxxxxxxxx>