[PATCH 08/12] tracing/probes: Reject array count on non-dereference string sources

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

The runtime array loop (FETCH_OP_LP_ARRAY) for string types requires a
preceding memory dereference instruction so it can advance the pointer
address on each iteration. Non-dereference string sources such as $comm,
immediate strings, and eprobe event fields cannot be indexed as pointer
arrays, but finalize_fetch_insn() still accepts an array count on them
and emits an invalid FETCH_OP_LP_ARRAY sequence.

Reject string array counts when the preceding operation is not a memory
dereference.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 kernel/trace/trace_probe.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index e62acf05a8ee..0f544d415153 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -1986,6 +1986,12 @@ static int finalize_fetch_insn(struct fetch_insn *code,
 			 * For the symstr, it doesn't need to dereference, thus
 			 * it just get the value.
 			 */
+			if (parg->count && (code->op != FETCH_OP_DEREF &&
+					    code->op != FETCH_OP_UDEREF)) {
+				trace_probe_log_err(ctx->offset + type_offset,
+						    BAD_STRING);
+				return -EINVAL;
+			}
 			code++;
 			if (code->op != FETCH_OP_NOP) {
 				trace_probe_log_err(ctx->offset, TOO_MANY_OPS);