Patch "fix race in drivers/char/random.c:get_reg()" has been added to the 4.4-stable tree

Patch "fix race in drivers/char/random.c:get_reg()" has been added to the 4.4-stable tree

[gregkh]

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 4.4-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-4.4 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 Tue Apr 10 10:31:53 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
@@ -886,12 +886,16 @@ 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-4.4/fix-race-in-drivers-char-random.c-get_reg.patch