tracing: Check field value in hist_field_name()

The function hist_field_name() cannot handle being passed a NULL field
parameter. It should never be NULL, but due to a previous bug, NULL was
passed to the function and the kernel crashed due to a NULL dereference.
Mark Rutland reported this to me on IRC.

The bug was fixed, but to prevent future bugs from crashing the kernel,
check the field and add a WARN_ON() if it is NULL.

Link: https://lkml.kernel.org/r/[email protected]
Cc: [email protected]
Cc: Masami Hiramatsu <[email protected]>
Cc: Andrew Morton <[email protected]>
Reported-by: Mark Rutland <[email protected]>
Fixes: c6afad49d127f ("tracing: Add hist trigger 'sym' and 'sym-offset' modifiers")
Tested-by: Mark Rutland <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 6e8ab726a7b5ef0d96a1e034ccc0747785090a50..486cca3c2b75450f23f8b680045421cf234d232f 100644 (file)
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1331,6 +1331,9 @@ static const char *hist_field_name(struct hist_field *field,
 {
        const char *field_name = "";
 
+       if (WARN_ON_ONCE(!field))
+               return field_name;
+
        if (level > 1)
                return field_name;