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Commit 508a9274 authored by Jeff Dike's avatar Jeff Dike Committed by Linus Torvalds
Browse files

uml: fix irqstack crash 



This patch fixes a crash caused by an interrupt coming in when an IRQ stack
is being torn down.  When this happens, handle_signal will loop, setting up
the IRQ stack again because the tearing down had finished, and handling
whatever signals had come in.

However, to_irq_stack returns a mask of pending signals to be handled, plus
bit zero is set if the IRQ stack was already active, and thus shouldn't be
torn down.  This causes a problem because when handle_signal goes around
the loop, sig will be zero, and to_irq_stack will duly set bit zero in the
returned mask, faking handle_signal into believing that it shouldn't tear
down the IRQ stack and return thread_info pointers back to their original
values.

This will eventually cause a crash, as the IRQ stack thread_info will
continue pointing to the original task_struct and an interrupt will look
into it after it has been freed.

The fix is to stop passing a signal number into to_irq_stack.  Rather, the
pending signals mask is initialized beforehand with the bit for sig already
set.  References to sig in to_irq_stack can be replaced with references to
the mask.

[akpm@linux-foundation.org: use UL]
Signed-off-by: default avatarJeff Dike <jdike@linux.intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 480eccf9

arch/um/include/kern_util.h

+1 −1
Original line number Diff line number Diff line
@@ -117,7 +117,7 @@ extern void sigio_handler(int sig, union uml_pt_regs *regs); 


extern void copy_sc(union uml_pt_regs *regs, void *from);



unsigned long to_irq_stack(int sig, unsigned long *mask_out);

extern unsigned long to_irq_stack(unsigned long *mask_out);

unsigned long from_irq_stack(int nested);



#endif

arch/um/kernel/irq.c

+4 −3
Original line number Diff line number Diff line
@@ -518,13 +518,13 @@ int init_aio_irq(int irq, char *name, irq_handler_t handler) 


static unsigned long pending_mask;



unsigned long to_irq_stack(int sig, unsigned long *mask_out)

unsigned long to_irq_stack(unsigned long *mask_out)

{

	struct thread_info *ti;

	unsigned long mask, old;

	int nested;



	mask = xchg(&pending_mask, 1 << sig);

	mask = xchg(&pending_mask, *mask_out);

	if(mask != 0){

		/* If any interrupts come in at this point, we want to

		 * make sure that their bits aren't lost by our
@@ -534,7 +534,7 @@ unsigned long to_irq_stack(int sig, unsigned long *mask_out) 
		 * and pending_mask contains a bit for each interrupt

		 * that came in.

		 */

		old = 1 << sig;

		old = *mask_out;

		do {

			old |= mask;

			mask = xchg(&pending_mask, old);
@@ -550,6 +550,7 @@ unsigned long to_irq_stack(int sig, unsigned long *mask_out) 


		task = cpu_tasks[ti->cpu].task;

		tti = task_thread_info(task);



		*ti = *tti;

		ti->real_thread = tti;

		task->stack = ti;

arch/um/os-Linux/signal.c

+2 −2
Original line number Diff line number Diff line
@@ -119,7 +119,7 @@ void (*handlers[_NSIG])(int sig, struct sigcontext *sc); 


void handle_signal(int sig, struct sigcontext *sc)

{

	unsigned long pending = 0;

	unsigned long pending = 1UL << sig;



	do {

		int nested, bail;
@@ -134,7 +134,7 @@ void handle_signal(int sig, struct sigcontext *sc) 
		 * have to return, and the upper handler will deal

		 * with this interrupt.

		 */

		bail = to_irq_stack(sig, &pending);

		bail = to_irq_stack(&pending);

		if(bail)

			return;