From: Dan Carpenter dan.carpenter@oracle.com
[ Upstream commit ca16b0fbb05242f18da9d810c07d3882ffed831c ]
Dan Carpenter reviewed the trace_stack.c code and figured he found an off by one bug.
"From reviewing the code, it seems possible for stack_trace_max.nr_entries to be set to .max_entries and in that case we would be reading one element beyond the end of the stack_dump_trace[] array. If it's not set to .max_entries then the bug doesn't affect runtime."
Although it looks to be the case, it is not. Because we have:
static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES+1] = { [0 ... (STACK_TRACE_ENTRIES)] = ULONG_MAX };
struct stack_trace stack_trace_max = { .max_entries = STACK_TRACE_ENTRIES - 1, .entries = &stack_dump_trace[0], };
And:
stack_trace_max.nr_entries = x; for (; x < i; x++) stack_dump_trace[x] = ULONG_MAX;
Even if nr_entries equals max_entries, indexing with it into the stack_dump_trace[] array will not overflow the array. But if it is the case, the second part of the conditional that tests stack_dump_trace[nr_entries] to ULONG_MAX will always be true.
By applying Dan's patch, it removes the subtle aspect of it and makes the if conditional slightly more efficient.
Link: http://lkml.kernel.org/r/20180620110758.crunhd5bfep7zuiz@kili.mountain
Signed-off-by: Dan Carpenter dan.carpenter@oracle.com Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/trace/trace_stack.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c index 719a52a4064a..ba662010542c 100644 --- a/kernel/trace/trace_stack.c +++ b/kernel/trace/trace_stack.c @@ -282,7 +282,7 @@ __next(struct seq_file *m, loff_t *pos) { long n = *pos - 1;
- if (n > stack_trace_max.nr_entries || stack_dump_trace[n] == ULONG_MAX) + if (n >= stack_trace_max.nr_entries || stack_dump_trace[n] == ULONG_MAX) return NULL;
m->private = (void *)n;