libtraceevent: Do not print zero length dynamic strings

Commit Message

Steven Rostedt June 16, 2021, 2:55 a.m. UTC

From: "Steven Rostedt (VMware)" <[e-mail]>

If a dynamic string happens to not have any length, which means that it
does not even have a null pointer, but the parsing code will still look at
the offset, and read the string at that location. If there's another
dynamic string after it, it will mistakenly report that next string as the
current one. This can be confusing, as the string being printed is not the
string expected.

Discovered this when playing with kprobes and exec arguments.

Fixes: ("tools/events: Add files to create libtraceevent.a")
Signed-off-by: Steven Rostedt (VMware) <[e-mail]>
---
 src/event-parse.c | 5 +++++
 1 file changed, 5 insertions(+)

Patch

diff --git a/src/event-parse.c b/src/event-parse.c
index 1217491..7a75e9b 100644
--- a/src/event-parse.c
+++ b/src/event-parse.c
@@ -4392,6 +4392,7 @@  static void print_str_arg(struct trace_seq *s, void *data, int size,
 		break;
 	case TEP_PRINT_STRING: {
 		int str_offset;
+		int len;
 
 		if (arg->string.offset == -1) {
 			struct tep_format_field *f;
@@ -4400,6 +4401,10 @@  static void print_str_arg(struct trace_seq *s, void *data, int size,
 			arg->string.offset = f->offset;
 		}
 		str_offset = data2host4(tep, *(unsigned int *)(data + arg->string.offset));
+		len = (str_offset >> 16) & 0xffff;
+		/* Do not attempt to save zero length dynamic strings */
+		if (!len)
+			break;
 		str_offset &= 0xffff;
 		print_str_to_seq(s, format, len_arg, ((char *)data) + str_offset);
 		break;