Messages in this thread Patch in this message | | | Subject | Re: [PATCH] locking/lockdep: Fix potential buffer overrun problem in stack_trace[] | From | Bart Van Assche <> | Date | Thu, 19 Dec 2019 18:57:13 -0800 |
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On 2019-12-19 10:28, Waiman Long wrote: > If the lockdep code is really running out of the stack_trace entries, > there is a possiblity that buffer overrun can happen and corrupt the ^^^^^^^^^^ possibility? > data immediately after stack_trace[]. > > If there is less than LOCK_TRACE_SIZE_IN_LONGS entries left before > the call to save_trace(), the max_entries computation will leave it > with a very large positive number because of its unsigned nature. The > subsequent call to stack_trace_save() will then corrupt the data after > stack_trace[]. Fix that by changing max_entries to a signed integer > and check for negative value before calling stack_trace_save(). > > Fixes: 12593b7467f9 ("locking/lockdep: Reduce space occupied by stack traces") > Signed-off-by: Waiman Long <longman@redhat.com> > --- > kernel/locking/lockdep.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > index 32282e7112d3..56e260a7582f 100644 > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -482,7 +482,7 @@ static struct lock_trace *save_trace(void) > struct lock_trace *trace, *t2; > struct hlist_head *hash_head; > u32 hash; > - unsigned int max_entries; > + int max_entries; > > BUILD_BUG_ON_NOT_POWER_OF_2(STACK_TRACE_HASH_SIZE); > BUILD_BUG_ON(LOCK_TRACE_SIZE_IN_LONGS >= MAX_STACK_TRACE_ENTRIES); > @@ -490,10 +490,8 @@ static struct lock_trace *save_trace(void) > trace = (struct lock_trace *)(stack_trace + nr_stack_trace_entries); > max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries - > LOCK_TRACE_SIZE_IN_LONGS; > - trace->nr_entries = stack_trace_save(trace->entries, max_entries, 3); > > - if (nr_stack_trace_entries >= MAX_STACK_TRACE_ENTRIES - > - LOCK_TRACE_SIZE_IN_LONGS - 1) { > + if (max_entries < 0) { > if (!debug_locks_off_graph_unlock()) > return NULL; > > @@ -502,6 +500,7 @@ static struct lock_trace *save_trace(void) > > return NULL; > } > + trace->nr_entries = stack_trace_save(trace->entries, max_entries, 3); > > hash = jhash(trace->entries, trace->nr_entries * > sizeof(trace->entries[0]), 0);
I'm not sure whether it is useful to call stack_trace_save() if max_entries == 0. How about changing the "max_entries < 0" test into "max_entries <= 0"?
Thanks,
Bart.
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