dd: Better handle user specified offsets that are too big

Following are the before and after operations for seekable files,
for the various erroneous offsets handled by this patch:

skip beyond end of file
  before: immediately exit(0);
  after : immediately printf("cannot skip to specified offset"); exit(0);

skip > max file size
  before: read whole file and exit(0);
  after : immediately printf("cannot skip: Invalid argument"); exit(1);
seek > max file size
  before: immediately printf("truncate error: EFBIG"); exit(1);
  after : immediately printf("truncate error: EFBIG"); exit(1);

skip > OFF_T_MAX
  before: read whole device/file and exit(0);
  after : immediately printf("cannot skip:"); exit(1);
seek > OFF_T_MAX
  before: immediately printf("truncate error: offset too large"); exit(1);
  after : immediately printf("truncate error: offset too large"); exit(1);

skip > device size
  before: read whole device and exit(0);
  after : immediately printf("cannot skip: Invalid argument"); exit(1);
seek > device size
  before: read whole device and printf("write error: ENOSPC"); exit(1);
  after : immediately printf("cannot seek: Invalid argument"); exit(1);

* NEWS: Summarize this change in behavior.
* src/dd.c (skip): Add error checking for large seek/skip offsets on
seekable files, rather than deferring to using read() to advance offset.
(dd_copy): Print a warning if skip past EOF, as per FIXME comment.
* test/Makefile.am: Add 2 new tests.
* tests/dd/seek-skip-past-file: Add tests for first 3 cases above.
* tests/dd/seek-skip-past-dev: Add root only test for last case above.

1 files changed, 4 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 83b8ed9a1..99fc182f8 100644
--- a/NEWS
+++ b/NEWS
@@ -38,6 +38,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   cp and mv: the --reply={yes,no,query} option has been removed.
   Using it has elicited a warning for the last three years.
 
+  dd: user specified offsets that are too big are handled better.
+  Previously, erroneous parameters to skip and seek could result
+  in redundant reading of the file with no warnings or errors.
+
   du: -H (initially equivalent to --si) is now equivalent to
   --dereference-args, and thus works as POSIX requires