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%3Ba=su...

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