Commit 9dfa7bba authored Apr 30, 2017 by Michael Schmitz Committed by Theodore Ts'o May 24, 2017

fix race in drivers/char/random.c:get_reg()



get_reg() can be reentered on architectures with prioritized interrupts
(m68k in this case), causing f->reg_index to be incremented after the
range check. Out of bounds memory access past the pt_regs struct results.
This will go mostly undetected unless access is beyond end of memory.

Prevent the race by disabling interrupts in get_reg().

Tested on m68k (Atari Falcon, and ARAnyM emulator).

Kudos to Geert Uytterhoeven for helping to trace this race.

Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

parent 08332893

drivers/char/random.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -1097,12 +1097,16 @@ static void add_interrupt_bench(cycles_t start)
		static __u32 get_reg(struct fast_pool f, struct pt_regs regs)
		{
		__u32 ptr = (__u32 ) regs;
		unsigned long flags;

		if (regs == NULL)
		return 0;
		local_irq_save(flags);
		if (f->reg_idx >= sizeof(struct pt_regs) / sizeof(__u32))
		f->reg_idx = 0;
		return *(ptr + f->reg_idx++);
		ptr += f->reg_idx++;
		local_irq_restore(flags);
		return *ptr;
		}

		void add_interrupt_randomness(int irq, int irq_flags)

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