cmd/internal/buildid: reject empty id

The loop that makes progress assumes that after matching an id
you should advance len(id) bytes in the file. If id is the empty string,
then it will match and advance 0 bytes repeatedly.

0-byte ids are not really build IDs, so just reject it outright.

Fixes #47852.

Change-Id: Ie44a3a51dec22e2f68fb72d54ead91be98000cfe
Reviewed-on: https://go-review.googlesource.com/c/go/+/344049
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

2 files changed, 11 insertions, 0 deletions

diff --git a/src/cmd/internal/buildid/buildid_test.go b/src/cmd/internal/buildid/buildid_test.go
index e832f9987e..4895a49e11 100644
--- a/src/cmd/internal/buildid/buildid_test.go
+++ b/src/cmd/internal/buildid/buildid_test.go
@@ -177,3 +177,11 @@ func TestExcludedReader(t *testing.T) {
 		}
 	}
 }
+
+func TestEmptyID(t *testing.T) {
+	r := strings.NewReader("aha!")
+	matches, hash, err := FindAndHash(r, "", 1000)
+	if matches != nil || hash != ([32]byte{}) || err == nil || !strings.Contains(err.Error(), "no id") {
+		t.Errorf("FindAndHash: want nil, [32]byte{}, no id specified, got %v, %v, %v", matches, hash, err)
+	}
+}
diff --git a/src/cmd/internal/buildid/rewrite.go b/src/cmd/internal/buildid/rewrite.go
index a7928959c4..8814950db0 100644
--- a/src/cmd/internal/buildid/rewrite.go
+++ b/src/cmd/internal/buildid/rewrite.go
@@ -22,6 +22,9 @@ func FindAndHash(r io.Reader, id string, bufSize int) (matches []int64, hash [32
 	if bufSize == 0 {
 		bufSize = 31 * 1024 // bufSize+little will likely fit in 32 kB
 	}
+	if len(id) == 0 {
+		return nil, [32]byte{}, fmt.Errorf("buildid.FindAndHash: no id specified")
+	}
 	if len(id) > bufSize {
 		return nil, [32]byte{}, fmt.Errorf("buildid.FindAndHash: buffer too small")
 	}