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authorDan Carpenter <dan.carpenter@oracle.com>2018-06-20 14:08:00 +0300
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2018-12-08 20:54:07 -0500
commitca16b0fbb05242f18da9d810c07d3882ffed831c (patch)
treeb48c71b974b5d1f18969ae01c7081e20bbbc1f29
parentb0e21a61d3196762b61f43ae994ffd255f646774 (diff)
downloadlinux-ca16b0fbb05242f18da9d810c07d3882ffed831c.tar.bz2
tracing: Have trace_stack nr_entries compare not be so subtle
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>
-rw-r--r--kernel/trace/trace_stack.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 2b0d1ee3241c..e2a153fc1afc 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -286,7 +286,7 @@ __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;