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@xxxxxxxxxxxxxxx> know about it. >From foo@baz Tue Apr 10 10:31:53 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 @@ -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@xxxxxxxxx are queue-4.4/fix-race-in-drivers-char-random.c-get_reg.patch