| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.9 106/310] fix race in drivers/char/random.c:get_reg() | Date | Wed, 11 Apr 2018 20:34:05 +0200 |
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4.9-stable review patch. If anyone has any objections, please let me know.
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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)
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