path: root/drivers/char/random.c
diff options
authorMichael Schmitz <schmitzmic@gmail.com>2017-04-30 19:49:21 +1200
committerTheodore Ts'o <tytso@mit.edu>2017-05-24 17:41:26 -0400
commit9dfa7bba35ac08a63565d58c454dccb7e1bb0a08 (patch)
treedc3c409bbdc76c8eef5da5e7c37eb311c76bc92d /drivers/char/random.c
parent08332893e37af6ae779367e78e444f8f9571511d (diff)
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/char/random.c')
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)