5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Steven Rostedt (Google) [ Upstream commit eca344a7362e0f34f179298fd8366bcd556eede1 ] 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 Tested-by: Brian Foster Fixes: 9a6944fee68e2 ("tracing: Add a verifier to check string pointers for trace events") Signed-off-by: Steven Rostedt (Google) Signed-off-by: Sasha Levin --- kernel/trace/trace.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 31d0abb1c9429..bfa6e2fe984b1 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -3586,12 +3586,17 @@ static char *trace_iter_expand_format(struct trace_iterator *iter) } /* 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; struct trace_event *trace_event; struct trace_event_call *event; + /* Ignore strings with no length */ + if (star && !len) + return true; + /* OK if part of the event data */ if ((addr >= (unsigned long)iter->ent) && (addr < (unsigned long)iter->ent + iter->ent_size)) @@ -3755,7 +3760,7 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt, * instead. See samples/trace_events/trace-events-sample.h * 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, show_buffer(&iter->seq))) { int ret; -- 2.53.0