debug/elf: use saferio.SliceCap when decoding ELF sections

This avoids allocating an overly large slice for corrupt input.

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

Updates #33121.

Change-Id: Ie2d947a3865d3499034286f2d08d3e3204015f3e
GitHub-Last-Rev: 6c62fc3cec1c6343c76f22f6a2a4ddae060fa2f4
GitHub-Pull-Request: golang/go#56405
Reviewed-on: https://go-review.googlesource.com/c/go/+/445076
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: 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: Heschi Kreinick <heschi@google.com>

diff --git a/src/debug/elf/file.go b/src/debug/elf/file.go
index 708980bc1c31be6299ad3246a97a163a1ad50901..7c5ac86c0a1aa8f74bc3e88fd84c44d51636f501 100644 (file)
--- a/src/debug/elf/file.go
+++ b/src/debug/elf/file.go
@@ -467,8 +467,12 @@ func NewFile(r io.ReaderAt) (*File, error) {
        }
 
        // Read section headers
-       f.Sections = make([]*Section, shnum)
-       names := make([]uint32, shnum)
+       c := saferio.SliceCap((*Section)(nil), uint64(shnum))
+       if c < 0 {
+               return nil, &FormatError{0, "too many sections", shnum}
+       }
+       f.Sections = make([]*Section, 0, c)
+       names := make([]uint32, 0, c)
        for i := 0; i < shnum; i++ {
                off := shoff + int64(i)*int64(shentsize)
                sr.Seek(off, seekStart)
@@ -479,7 +483,7 @@ func NewFile(r io.ReaderAt) (*File, error) {
                        if err := binary.Read(sr, f.ByteOrder, sh); err != nil {
                                return nil, err
                        }
-                       names[i] = sh.Name
+                       names = append(names, sh.Name)
                        s.SectionHeader = SectionHeader{
                                Type:      SectionType(sh.Type),
                                Flags:     SectionFlag(sh.Flags),
@@ -496,7 +500,7 @@ func NewFile(r io.ReaderAt) (*File, error) {
                        if err := binary.Read(sr, f.ByteOrder, sh); err != nil {
                                return nil, err
                        }
-                       names[i] = sh.Name
+                       names = append(names, sh.Name)
                        s.SectionHeader = SectionHeader{
                                Type:      SectionType(sh.Type),
                                Flags:     SectionFlag(sh.Flags),
@@ -544,7 +548,7 @@ func NewFile(r io.ReaderAt) (*File, error) {
                        }
                }
 
-               f.Sections[i] = s
+               f.Sections = append(f.Sections, s)
        }
 
        if len(f.Sections) == 0 {