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Commit 9dfa7bba authored by Michael Schmitz's avatar Michael Schmitz Committed by Theodore Ts'o
Browse files

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: default avatarMichael Schmitz <schmitzmic@gmail.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 08332893

drivers/char/random.c

+5 −1
Original line number Original line 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)

static __u32 get_reg(struct fast_pool *f, struct pt_regs *regs)

{

{

	__u32 *ptr = (__u32 *) regs;

	__u32 *ptr = (__u32 *) regs;

	unsigned long flags;





	if (regs == NULL)

	if (regs == NULL)

		return 0;

		return 0;

	local_irq_save(flags);

	if (f->reg_idx >= sizeof(struct pt_regs) / sizeof(__u32))

	if (f->reg_idx >= sizeof(struct pt_regs) / sizeof(__u32))

		f->reg_idx = 0;

		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)

void add_interrupt_randomness(int irq, int irq_flags)