debug/buildinfo: use saferio in ReadData methods

This avoids a very large memory allocation if corrupt data says that
we need to read a very long string.

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

For golang#47653
Fixes golang#58886

Change-Id: I4e80ba62a6416d010c8804e4f49ae81bdafaadb8
Reviewed-on: https://go-review.googlesource.com/c/go/+/473657
Run-TryBot: Ian Lance Taylor <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: ianlancetaylor

src/debug/buildinfo/buildinfo.go

@@ -19,6 +19,7 @@ import (
 	"encoding/binary"
 	"errors"
 	"fmt"
+	"internal/saferio"
 	"internal/xcoff"
 	"io"
 	"io/fs"
@@ -260,12 +261,7 @@ func (x *elfExe) ReadData(addr, size uint64) ([]byte, error) {
 			if n > size {
 				n = size
 			}
-			data := make([]byte, n)
-			_, err := prog.ReadAt(data, int64(addr-prog.Vaddr))
-			if err != nil {
-				return nil, err
-			}
-			return data, nil
+			return saferio.ReadDataAt(prog, n, int64(addr-prog.Vaddr))
 		}
 	}
 	return nil, errUnrecognizedFormat
@@ -308,12 +304,7 @@ func (x *peExe) ReadData(addr, size uint64) ([]byte, error) {
 			if n > size {
 				n = size
 			}
-			data := make([]byte, n)
-			_, err := sect.ReadAt(data, int64(addr-uint64(sect.VirtualAddress)))
-			if err != nil {
-				return nil, errUnrecognizedFormat
-			}
-			return data, nil
+			return saferio.ReadDataAt(sect, n, int64(addr-uint64(sect.VirtualAddress)))
 		}
 	}
 	return nil, errUnrecognizedFormat
@@ -360,12 +351,7 @@ func (x *machoExe) ReadData(addr, size uint64) ([]byte, error) {
 			if n > size {
 				n = size
 			}
-			data := make([]byte, n)
-			_, err := seg.ReadAt(data, int64(addr-seg.Addr))
-			if err != nil {
-				return nil, err
-			}
-			return data, nil
+			return saferio.ReadDataAt(seg, n, int64(addr-seg.Addr))
 		}
 	}
 	return nil, errUnrecognizedFormat
@@ -401,12 +387,7 @@ func (x *xcoffExe) ReadData(addr, size uint64) ([]byte, error) {
 			if n > size {
 				n = size
 			}
-			data := make([]byte, n)
-			_, err := sect.ReadAt(data, int64(addr-sect.VirtualAddress))
-			if err != nil {
-				return nil, err
-			}
-			return data, nil
+			return saferio.ReadDataAt(sect, n, int64(addr-sect.VirtualAddress))
 		}
 	}
 	return nil, errors.New("address not mapped")
@@ -438,12 +419,7 @@ func (x *plan9objExe) ReadData(addr, size uint64) ([]byte, error) {
 			if n > size {
 				n = size
 			}
-			data := make([]byte, n)
-			_, err := sect.ReadAt(data, int64(addr-uint64(sect.Offset)))
-			if err != nil {
-				return nil, err
-			}
-			return data, nil
+			return saferio.ReadDataAt(sect, n, int64(addr-uint64(sect.Offset)))
 		}
 	}
 	return nil, errors.New("address not mapped")