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From: Michael Schmitz <schmitzmic@gmail.com>
Date: Tue, 10 Apr 2018 08:30:19 +1200
Message-ID: <CAOmrzkKmk99=nLHkWNy=YRpnygqyTX-Zbu6mfuDsS7TXFtYbXg@mail.gmail.com>
Subject: Re: Patch "fix race in drivers/char/random.c:get_reg()" has been
 added to the 4.9-stable tree
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Sasha Levin <alexander.levin@microsoft.com>,
        "Theodore Ts'o" <tytso@mit.edu>, stable@vger.kernel.org,
        stable-commits@vger.kernel.org
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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@linuxfoundation.org> 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@vger.kernel.org> know about it.
>
>
> 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)
>
>
> Patches currently in stable-queue which might be from schmitzmic@gmail.com are
>
> queue-4.9/fix-race-in-drivers-char-random.c-get_reg.patch