| From foo@baz Mon Apr 9 17:09:24 CEST 2018 |
| From: Michael Schmitz <schmitzmic@gmail.com> |
| Date: Sun, 30 Apr 2017 19:49:21 +1200 |
| Subject: fix race in drivers/char/random.c:get_reg() |
| |
| From: Michael Schmitz <schmitzmic@gmail.com> |
| |
| |
| [ Upstream commit 9dfa7bba35ac08a63565d58c454dccb7e1bb0a08 ] |
| |
| 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> |
| Signed-off-by: Sasha Levin <alexander.levin@microsoft.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| drivers/char/random.c | 6 +++++- |
| 1 file changed, 5 insertions(+), 1 deletion(-) |
| |
| --- a/drivers/char/random.c |
| +++ b/drivers/char/random.c |
| @@ -1115,12 +1115,16 @@ static void add_interrupt_bench(cycles_t |
| 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) |
