Greg,
please do also apply Linus' final fix to this issue - commit 92e75428ffc90e2a
("random: use lockless method of accessing and updating f->reg_idx").
Cheers,
Michael
On Tue, Apr 10, 2018 at 7:58 AM, <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> This is a note to let you know that I've just added the patch titled
>
> fix race in drivers/char/random.c:get_reg()
>
> to the 4.9-stable tree which can be found at:
> http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
>
> The filename of the patch is:
> fix-race-in-drivers-char-random.c-get_reg.patch
> and it can be found in the queue-4.9 subdirectory.
>
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@xxxxxxxxxxxxxxx> know about it.
>
>
> From foo@baz Mon Apr 9 17:09:24 CEST 2018
> From: Michael Schmitz <schmitzmic@xxxxxxxxx>
> Date: Sun, 30 Apr 2017 19:49:21 +1200
> Subject: fix race in drivers/char/random.c:get_reg()
>
> From: Michael Schmitz <schmitzmic@xxxxxxxxx>
>
>
> [ 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@xxxxxxxxx>
> Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
> 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)
>
>
> Patches currently in stable-queue which might be from schmitzmic@xxxxxxxxx are
>
> queue-4.9/fix-race-in-drivers-char-random.c-get_reg.patch