perf probe: Add protection to avoid endless loop

if dwarf_offdie() returns NULL, the continue statement forces the next
iteration of the loop without updating the 'off' variable. It will cause
an endless loop in the process of traversing the compile unit.  So add
exception protection for looping CUs.

Signed-off-by: Jianlin Lv <Jianlin.Lv@arm.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: jianlin.lv@arm.com
Link: http://lore.kernel.org/lkml/20210203145702.1219509-1-Jianlin.Lv@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/probe-finder.c

@@ -1187,8 +1187,10 @@ static int debuginfo__find_probe_location(struct debuginfo *dbg,
 	while (!dwarf_nextcu(dbg->dbg, off, &noff, &cuhl, NULL, NULL, NULL)) {
 		/* Get the DIE(Debugging Information Entry) of this CU */
 		diep = dwarf_offdie(dbg->dbg, off + cuhl, &pf->cu_die);
-		if (!diep)
+		if (!diep) {
+			off = noff;
 			continue;
+		}
 
 		/* Check if target file is included. */
 		if (pp->file)
@@ -1949,8 +1951,10 @@ int debuginfo__find_line_range(struct debuginfo *dbg, struct line_range *lr)
 
 		/* Get the DIE(Debugging Information Entry) of this CU */
 		diep = dwarf_offdie(dbg->dbg, off + cuhl, &lf.cu_die);
-		if (!diep)
+		if (!diep) {
+			off = noff;
 			continue;
+		}
 
 		/* Check if target file is included. */
 		if (lr->file)