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tracing: Have trace event string test handle zero length strings 

If a trace event has in its TP_printk():

 "%*.s", len, len ? __get_str(string) : NULL

It is perfectly valid if len is zero and passing in the NULL.
Unfortunately, the runtime string check at time of reading the trace sees
the NULL and flags it as a bad string and produces a WARN_ON().

Handle this case by passing into the test function if the format has an
asterisk (star) and if so, if the length is zero, then mark it as safe.

Link: https://lore.kernel.org/all/YjsWzuw5FbWPrdqq@bfoster/

Cc: stable@vger.kernel.org
Reported-by: Brian Foster <bfoster@redhat.com>
Tested-by: Brian Foster <bfoster@redhat.com>
Fixes: 9a6944fee6 ("tracing: Add a verifier to check string pointers for trace events")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (Google) 2022-03-23 10:32:51 -04:00
parent 78cbc65132
commit eca344a736
1 changed files with 7 additions and 2 deletions
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9
kernel/trace/trace.c
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@ -3663,12 +3663,17 @@ static char *trace_iter_expand_format(struct trace_iterator *iter)
} }
/* Returns true if the string is safe to dereference from an event */ /* Returns true if the string is safe to dereference from an event */
static bool trace_safe_str(struct trace_iterator *iter, const char *str) static bool trace_safe_str(struct trace_iterator *iter, const char *str,
bool star, int len)
{ {
unsigned long addr = (unsigned long)str; unsigned long addr = (unsigned long)str;
struct trace_event *trace_event; struct trace_event *trace_event;
struct trace_event_call *event; struct trace_event_call *event;
/* Ignore strings with no length */
if (star && !len)
return true;
/* OK if part of the event data */ /* OK if part of the event data */
if ((addr >= (unsigned long)iter->ent) && if ((addr >= (unsigned long)iter->ent) &&
(addr < (unsigned long)iter->ent + iter->ent_size)) (addr < (unsigned long)iter->ent + iter->ent_size))
@ -3854,7 +3859,7 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
* instead. See samples/trace_events/trace-events-sample.h * instead. See samples/trace_events/trace-events-sample.h
* for reference. * for reference.
*/ */
if (WARN_ONCE(!trace_safe_str(iter, str), if (WARN_ONCE(!trace_safe_str(iter, str, star, len),
"fmt: '%s' current_buffer: '%s'", "fmt: '%s' current_buffer: '%s'",
fmt, show_buffer(&iter->seq))) { fmt, show_buffer(&iter->seq))) {
int ret; int ret;