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| author |   Michael Schmitz <schmitzmic@gmail.com> | 2017-04-30 19:49:21 +1200 |
|---|---|---|
| committer |   Theodore Ts'o <tytso@mit.edu> | 2017-05-24 17:41:26 -0400 |
| commit | 9dfa7bba35ac08a63565d58c454dccb7e1bb0a08 (patch) | |
| tree | dc3c409bbdc76c8eef5da5e7c37eb311c76bc92d /drivers | |
| parent | Linux 4.12-rc2 (diff) | |
| download | linux-dev-9dfa7bba35ac08a63565d58c454dccb7e1bb0a08.tar.xz linux-dev-9dfa7bba35ac08a63565d58c454dccb7e1bb0a08.zip | |
fix race in drivers/char/random.c:get_reg()
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>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/char/random.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c index 0ab024918907..a561f0c2f428 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1097,12 +1097,16 @@ static void add_interrupt_bench(cycles_t start) 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) |