tracing: Have event format check not flag %p* on __get_dynamic_array()

The print fmt check against trace events to make sure that the format does
not use pointers that may be freed from the time of the trace to the time
the event is read, gives a false positive on %pISpc when reading data that
was saved in __get_dynamic_array() when it is perfectly fine to do so, as
the data being read is on the ring buffer.

Link: https://lore.kernel.org/all/20220407144524.2a592ed6@canb.auug.org.au/
Cc: stable@vger.kernel.org
Fixes: 5013f454a352c ("tracing: Add check of trace event print fmts for dereferencing pointers")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 78f313b..d591348 100644 (file)
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -392,12 +392,6 @@ static void test_event_printk(struct trace_event_call *call)
                        if (!(dereference_flags & (1ULL << arg)))
                                goto next_arg;
 
-                       /* Check for __get_sockaddr */;
-                       if (str_has_prefix(fmt + i, "__get_sockaddr(")) {
-                               dereference_flags &= ~(1ULL << arg);
-                               goto next_arg;
-                       }
-
                        /* Find the REC-> in the argument */
                        c = strchr(fmt + i, ',');
                        r = strstr(fmt + i, "REC->");
@@ -413,7 +407,14 @@ static void test_event_printk(struct trace_event_call *call)
                                a = strchr(fmt + i, '&');
                                if ((a && (a < r)) || test_field(r, call))
                                        dereference_flags &= ~(1ULL << arg);
+                       } else if ((r = strstr(fmt + i, "__get_dynamic_array(")) &&
+                                  (!c || r < c)) {
+                               dereference_flags &= ~(1ULL << arg);
+                       } else if ((r = strstr(fmt + i, "__get_sockaddr(")) &&
+                                  (!c || r < c)) {
+                               dereference_flags &= ~(1ULL << arg);
                        }
+
                next_arg:
                        i--;
                        arg++;