perf trace-event: Fix infinite loop in skip()

skip() ignores do_read()'s return value and unconditionally
subtracts the requested chunk size from 'size' on every iteration.
This was previously bounded by size being 'int': a maliciously
large 64-bit value was truncated on assignment, capping the loop
early by accident.

Now that size is size_t, a crafted file supplying a very large
size causes skip() to keep requesting BUFSIZ-sized reads and
subtracting BUFSIZ from size regardless of whether do_read()
actually succeeds, spinning indefinitely even after EOF or a read
error.

Check do_read()'s return value and break out of the loop on
failure or EOF, so forward progress is only counted when a read
actually succeeds.

Signed-off-by: Tanushree Shah <tshah@linux.ibm.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/util/trace-event-read.c

@@ -72,12 +72,16 @@ static ssize_t do_read(void *data, size_t size)
 static void skip(size_t size)
 {
 	char buf[BUFSIZ];
-	size_t r;
+	ssize_t ret;
 
 	while (size) {
-		r = size > BUFSIZ ? BUFSIZ : size;
-		do_read(buf, r);
-		size -= r;
+		size_t len = size > BUFSIZ ? BUFSIZ : size;
+
+		ret = do_read(buf, len);
+		if (ret <= 0)
+			break;
+
+		size -= ret;
 	}
 }