proc/core: off-by-one error reading ELF core files (#2333)

core.(*splicedMemory).ReadMemory checked the entry interval
erroneously when dealing with contiguous entries.

pkg/proc/core/core.go

@@ -95,7 +95,7 @@ func (r *splicedMemory) Add(reader proc.MemoryReader, off, length uint64) {
 func (r *splicedMemory) ReadMemory(buf []byte, addr uint64) (n int, err error) {
 	started := false
 	for _, entry := range r.readers {
-		if entry.offset+entry.length < addr {
+		if entry.offset+entry.length <= addr {
 			if !started {
 				continue
 			}

pkg/proc/core/core_test.go

@@ -146,6 +146,56 @@ func TestSplicedReader(t *testing.T) {
 			}
 		})
 	}
+
+	// Test some ReadMemory errors
+
+	mem := &splicedMemory{}
+	for _, region := range []region{
+		{[]byte{0xa1, 0xa2, 0xa3, 0xa4}, 0x1000, 4},
+		{[]byte{0xb1, 0xb2, 0xb3, 0xb4}, 0x1004, 4},
+		{[]byte{0xc1, 0xc2, 0xc3, 0xc4}, 0x1010, 4},
+	} {
+		r := bytes.NewReader(region.data)
+		mem.Add(&offsetReaderAt{r, region.off}, region.off, region.length)
+	}
+
+	got := make([]byte, 4)
+
+	// Read before the first mapping
+	_, err := mem.ReadMemory(got, 0x900)
+	if err == nil || !strings.HasPrefix(err.Error(), "error while reading spliced memory at 0x900") {
+		t.Errorf("Read before the start of memory didn't fail (or wrong error): %v", err)
+	}
+
+	// Read after the last mapping
+	_, err = mem.ReadMemory(got, 0x1100)
+	if err == nil || (err.Error() != "offset 4352 did not match any regions") {
+		t.Errorf("Read after the end of memory didn't fail (or wrong error): %v", err)
+	}
+
+	// Read at the start of the first entry
+	_, err = mem.ReadMemory(got, 0x1000)
+	if err != nil || !bytes.Equal(got, []byte{0xa1, 0xa2, 0xa3, 0xa4}) {
+		t.Errorf("Reading at the start of the first entry: %v %#x", err, got)
+	}
+
+	// Read at the start of the second entry
+	_, err = mem.ReadMemory(got, 0x1004)
+	if err != nil || !bytes.Equal(got, []byte{0xb1, 0xb2, 0xb3, 0xb4}) {
+		t.Errorf("Reading at the start of the second entry: %v %#x", err, got)
+	}
+
+	// Read straddling entries 1 and 2
+	_, err = mem.ReadMemory(got, 0x1002)
+	if err != nil || !bytes.Equal(got, []byte{0xa3, 0xa4, 0xb1, 0xb2}) {
+		t.Errorf("Straddled read of the second entry: %v %#x", err, got)
+	}
+
+	// Read past the end of the second entry
+	_, err = mem.ReadMemory(got, 0x1007)
+	if err == nil || !strings.HasPrefix(err.Error(), "error while reading spliced memory at 0x1008") {
+		t.Errorf("Read into gap: %v", err)
+	}
 }
 
 func withCoreFile(t *testing.T, name, args string) *proc.Target {