debug/macho: don't crash if dynamic symtab with no symtab

No test case because the problem can only happen for invalid data. Let
the fuzzer find cases like this.

For #47653
Fixes #58642

Change-Id: I19fee0dc9bd6239b520c15182b8f1e57bb0049bb
Reviewed-on: https://go-review.googlesource.com/c/go/+/470397
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>

diff --git a/src/debug/macho/file.go b/src/debug/macho/file.go
index 9806c270bfadc1033846e715a0ba32a27a00b2be..3e339c32c6a2f3f96b80bd94ef695d6c738c089c 100644 (file)
--- a/src/debug/macho/file.go
+++ b/src/debug/macho/file.go
@@ -350,7 +350,9 @@ func NewFile(r io.ReaderAt) (*File, error) {
                        if err := binary.Read(b, bo, &hdr); err != nil {
                                return nil, err
                        }
-                       if hdr.Iundefsym > uint32(len(f.Symtab.Syms)) {
+                       if f.Symtab == nil {
+                               return nil, &FormatError{offset, "dynamic symbol table seen before any ordinary symbol table", nil}
+                       } else if hdr.Iundefsym > uint32(len(f.Symtab.Syms)) {
                                return nil, &FormatError{offset, fmt.Sprintf(
                                        "undefined symbols index in dynamic symbol table command is greater than symbol table length (%d > %d)",
                                        hdr.Iundefsym, len(f.Symtab.Syms)), nil}