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>
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 0ab0249..a561f0c 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1097,12 +1097,16 @@
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)