[syserr] Fix SIGBUS on syserr.FromError

Fix syzcaller panic SIGBUS on error handling. Done by
adding an interface, errors.GuestError, which errors can
implement in order to be compared against each other.

PiperOrigin-RevId: 393867554

pkg/syserr/BUILD

@@ -14,6 +14,7 @@ go_library(
         "//pkg/abi/linux/errno",
         "//pkg/errors",
         "//pkg/errors/linuxerr",
+        "//pkg/safecopy",
         "//pkg/tcpip",
         "@org_golang_x_sys//unix:go_default_library",
     ],

pkg/syserr/syserr.go

@@ -24,6 +24,7 @@ import (
 	"gvisor.dev/gvisor/pkg/abi/linux/errno"
 	"gvisor.dev/gvisor/pkg/errors"
 	"gvisor.dev/gvisor/pkg/errors/linuxerr"
+	"gvisor.dev/gvisor/pkg/safecopy"
 )
 
 // Error represents an internal error.
@@ -278,15 +279,18 @@ func FromError(err error) *Error {
 	if err == nil {
 		return nil
 	}
-	if errno, ok := err.(unix.Errno); ok {
-		return FromHost(errno)
+
+	switch e := err.(type) {
+	case unix.Errno:
+		return FromHost(e)
+	case *errors.Error:
+		return FromHost(unix.Errno(e.Errno()))
+	case safecopy.SegvError, safecopy.BusError, safecopy.AlignmentError:
+		return FromHost(unix.EFAULT)
 	}
 
-	if linuxErr, ok := err.(*errors.Error); ok {
-		return FromHost(unix.Errno(linuxErr.Errno()))
-	}
-
-	panic("unknown error: " + err.Error())
+	msg := fmt.Sprintf("err: %s type: %T", err.Error(), err)
+	panic(msg)
 }
 
 // ConvertIntr converts the provided error code (err) to another one (intr) if

test/syscalls/linux/BUILD

@@ -3293,9 +3293,12 @@ cc_library(
     ],
     deps = [
         ":unix_domain_socket_test_util",
+        "//test/util:file_descriptor",
+        "//test/util:memory_util",
         "//test/util:socket_util",
         "@com_google_absl//absl/strings",
         gtest,
+        "//test/util:temp_path",
         "//test/util:test_util",
         "//test/util:thread_util",
     ],

test/syscalls/linux/socket_unix.cc

@@ -27,7 +27,10 @@
 #include "gtest/gtest.h"
 #include "absl/strings/string_view.h"
 #include "test/syscalls/linux/unix_domain_socket_test_util.h"
+#include "test/util/file_descriptor.h"
+#include "test/util/memory_util.h"
 #include "test/util/socket_util.h"
+#include "test/util/temp_path.h"
 #include "test/util/test_util.h"
 #include "test/util/thread_util.h"
 
@@ -268,6 +271,18 @@ TEST_P(UnixSocketPairTest, SocketReopenFromProcfs) {
   }
 }
 
+// Repro for b/196804997.
+TEST_P(UnixSocketPairTest, SendFromMmapBeyondEof) {
+  TempPath file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
+  FileDescriptor fd = ASSERT_NO_ERRNO_AND_VALUE(Open(file.path(), O_RDONLY));
+  Mapping m = ASSERT_NO_ERRNO_AND_VALUE(
+      Mmap(nullptr, kPageSize, PROT_READ, MAP_SHARED, fd.get(), 0));
+
+  auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
+  ASSERT_THAT(send(sockets->first_fd(), m.ptr(), m.len(), 0),
+              SyscallFailsWithErrno(EFAULT));
+}
+
 }  // namespace
 
 }  // namespace testing