Add checks to prevent potential null dereferences of buf->stop_te
and buf->intr_te in pt_buffer_reset_markers function.

Smatch reported possible null dereferences of buf->stop_te and
buf->intr_te in the pt_buffer_reset_markers() and when i checked
both pointers were checked for null dereferences in earlier lines
however,after calling pt_topa_entry_for_page() where its return
value is NULL in certain conditions there were no checks for further
buf->stop_te and buf->intr_te uses which could potentially be null
dereferenced.

To avoid null dereference add checks after each pt_topa_entry_for_page()
call to safely handle null returns and also add checks where there was
direct dereference of the pointers.

Reported-by: Smatch static checker <smatch@kernel.org>
Signed-off-by: Shi Hao <i.shihao.999@gmail.com>
---
 arch/x86/events/intel/pt.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index e8cf29d2b10c..2b7d5d118b48 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -1148,7 +1148,8 @@ static int pt_buffer_reset_markers(struct pt_buffer *buf,
 	if (idx != buf->stop_pos) {
 		buf->stop_pos = idx;
 		buf->stop_te = pt_topa_entry_for_page(buf, idx);
-		buf->stop_te = pt_topa_prev_entry(buf, buf->stop_te);
+		if (buf->stop_te)
+			buf->stop_te = pt_topa_prev_entry(buf, buf->stop_te);
 	}

 	wakeup = handle->wakeup >> PAGE_SHIFT;
@@ -1162,12 +1163,16 @@ static int pt_buffer_reset_markers(struct pt_buffer *buf,
 	if (idx != buf->intr_pos) {
 		buf->intr_pos = idx;
 		buf->intr_te = pt_topa_entry_for_page(buf, idx);
-		buf->intr_te = pt_topa_prev_entry(buf, buf->intr_te);
+		if (buf->intr_te)
+			buf->intr_te = pt_topa_prev_entry(buf, buf->intr_te);
 	}

-	buf->stop_te->stop = 1;
-	buf->stop_te->intr = 1;
-	buf->intr_te->intr = 1;
+	if (buf->stop_te) {
+		buf->stop_te->stop = 1;
+		buf->stop_te->intr = 1;
+	}
+	if (buf->intr_te)
+		buf->intr_te->intr = 1;

 	return 0;
 }
--
2.51.0