tracing: Fix kernel crash while using empty filter with perf

Kernel is crashing when user tries to record 'ftrace:function' event
with empty filter:

  # perf record -e ftrace:function --filter="" ls

  # dmesg
  BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
  Oops: 0000 [#1] SMP PTI
  ...
  RIP: 0010:ftrace_profile_set_filter+0x14b/0x2d0
  RSP: 0018:ffffa4a7c0da7d20 EFLAGS: 00010246
  RAX: ffffa4a7c0da7d64 RBX: 0000000000000000 RCX: 0000000000000006
  RDX: 0000000000000000 RSI: 0000000000000092 RDI: ffff8c48ffc968f0
  ...
  Call Trace:
   _perf_ioctl+0x54a/0x6b0
   ? rcu_all_qs+0x5/0x30
  ...

After patch:
  # perf record -e ftrace:function --filter="" ls
  failed to set filter "" on event ftrace:function with 22 (Invalid argument)

Also, if user tries to echo "" > filter, it used to throw an error.
This behavior got changed by commit 80765597bc58 ("tracing: Rewrite
filter logic to be simpler and faster"). This patch restores the
behavior as a side effect:

Before patch:
  # echo "" > filter
  #

After patch:
  # echo "" > filter
  bash: echo: write error: Invalid argument
  #

Link: http://lkml.kernel.org/r/20180420150758.19787-1-ravi.bangoria@linux.ibm.com
Fixes: 80765597bc58 ("tracing: Rewrite filter logic to be simpler and faster")
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 9b4716bb8bb02fb93d9fd449e0969eaeb8c2fca8..1f951b3df60c59051fdeec23d0257fe2b2487e1b 100644 (file)
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1499,14 +1499,14 @@ static int process_preds(struct trace_event_call *call,
                return ret;
        }
 
-       if (!nr_preds) {
-               prog = NULL;
-       } else {
-               prog = predicate_parse(filter_string, nr_parens, nr_preds,
+       if (!nr_preds)
+               return -EINVAL;
+
+       prog = predicate_parse(filter_string, nr_parens, nr_preds,
                               parse_pred, call, pe);
-               if (IS_ERR(prog))
-                       return PTR_ERR(prog);
-       }
+       if (IS_ERR(prog))
+               return PTR_ERR(prog);
+
        rcu_assign_pointer(filter->prog, prog);
        return 0;
 }