dd: improve integer overflow checking

* src/dd.c: Prefer signed to unsigned types where either will do,
as this helps improve checking with gcc -fsanitize=undefined.
Limit the signed types to their intended ranges.
(MAX_BLOCKSIZE): Don’t exceed IDX_MAX - slop either.
(input_offset_overflow): Remove; overflow now denoted by negative.
(parse_integer): Return INTMAX_MAX on overflow, instead of unspecified.
Do not falsely report overflow for ‘00x99999999999999999999999999999’.
* tests/dd/misc.sh: New test for 00xBIG.
* tests/dd/skip-seek-past-file.sh: Adjust to new diagnostic wording.
New test for BIGxBIG.

tests/dd/misc.sh

@@ -19,6 +19,7 @@
 
 . "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
 print_ver_ dd
+export LC_ALL=C
 
 tmp_in=dd-in
 tmp_in2=dd-in2
@@ -98,7 +99,7 @@ test "$outbytes" -eq 3 || fail=1
 # A delay is required to trigger a failure.
 # There might be some missed failures but it's unlikely.
 (echo a; sleep .1; echo b) \
-  | env LC_ALL=C dd bs=4 status=noxfer iflag=fullblock >out 2>err || fail=1
+  | dd bs=4 status=noxfer iflag=fullblock >out 2>err || fail=1
 printf 'a\nb\n' > out_ok || framework_failure_
 echo "1+0 records in
 1+0 records out" > err_ok || framework_failure_
@@ -116,5 +117,11 @@ dd: warning: '0x' is a zero multiplier; use '00x' if that is intended
 EOF
 compare exp err || fail=1
 
+echo "0+0 records in
+0+0 records out" >err_ok || framework_failure_
+big=9999999999999999999999999999999999999999999999999999999999999
+dd if=$tmp_in of=$tmp_out count=00x$big status=noxfer 2>err || fail=1
+compare /dev/null $tmp_out || fail=1
+compare err_ok err || fail=1
 
 Exit $fail

tests/dd/skip-seek-past-file.sh

@@ -20,7 +20,7 @@
 print_ver_ dd
 require_sparse_support_ # for 'truncate --size=$OFF_T_MAX'
 eval $(getlimits) # for OFF_T limits
-
+export LC_ALL=C
 
 printf "1234" > file || framework_failure_
 
@@ -65,8 +65,11 @@ compare err_ok err || fail=1
 
 # skipping > OFF_T_MAX should fail immediately
 dd bs=1 skip=$OFF_T_OFLOW count=0 status=noxfer < file 2> err && fail=1
-# error message should be "... cannot skip: strerror(EOVERFLOW)"
-grep "cannot skip:" err >/dev/null || fail=1
+# error message should be "... invalid number: strerror(EOVERFLOW)"
+grep "invalid number:" err >/dev/null || fail=1
+dd bs=1 skip=${OFF_T_OFLOW}x$OFF_T_OFLOW count=0 status=noxfer < file 2> err &&
+    fail=1
+grep "invalid number:" err >/dev/null || fail=1
 
 # skipping > max file size should fail immediately
 if ! truncate --size=$OFF_T_MAX in 2>/dev/null; then