From: Michael Schmitz Date: Sun, 30 Apr 2017 07:49:21 +0000 (+1200) Subject: fix race in drivers/char/random.c:get_reg() X-Git-Tag: v4.12-rc4~12^2 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=9dfa7bba35ac0;p=karo-tx-linux.git 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 Signed-off-by: Theodore Ts'o --- diff --git a/drivers/char/random.c b/drivers/char/random.c index 0ab024918907..a561f0c2f428 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -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)