Fix bugs related to 'uname -d' in the 'uname' builtin (#251)

This commit fixes a bug in the ksh uname builtin's -d option that could
change the output of -o (I was only able to reproduce this on Linux):
    $ builtin uname
    $ uname -o
    GNU/Linux
    $ uname -d
    (none)
    $ uname -o
    (none)
I identified this patch from ksh2020 as a fix for this bug:
<https://github.com/att/ast/pull/1187>
The linked patch was meant to fix a crash in 'uname -d', although I've
had no luck reproducing it: <https://github.com/att/ast/issues/1184>

src/lib/libcmd/uname.c:
- Pass correct buffer to getdomainname() while executing uname -d.

src/cmd/ksh93/tests/builtins.sh:
- Add a regression test for the reported 'uname -d' crash.
- Add a regression test for the output of 'uname -o' after 'uname -d'.
- To handle potential crashes when running the regression tests in older
  versions of ksh, fork the command substitutions that run 'uname -d'.

NEWS

@@ -3,6 +3,14 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2021-04-03:
+
+- Fixed a bug that caused the uname builtin's -d option to change the output
+  of the -o option.
+
+- Fixed a possible crash that could occur when showing the domain name
+  with the uname builtin's -d option.
+
 2021-03-31:
 
 - Fixed a bug that caused 'cd -' to ignore the current value of $OLDPWD

src/cmd/ksh93/include/version.h

@@ -20,7 +20,7 @@
 
 #define SH_RELEASE_FORK	"93u+m"		/* only change if you develop a new ksh93 fork */
 #define SH_RELEASE_SVER	"1.0.0-alpha"	/* semantic version number: https://semver.org */
-#define SH_RELEASE_DATE	"2021-03-31"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2021-04-03"	/* must be in this format for $((.sh.version)) */
 #define SH_RELEASE_CPYR	"(c) 2020-2021 Contributors to ksh " SH_RELEASE_FORK
 
 /* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */

src/cmd/ksh93/tests/builtins.sh

@@ -1139,5 +1139,22 @@ got=$(
 	err_exit "OLDPWD and/or PWD fail to survive subshare" \
 	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
 
+# ======
+# Test for bugs related to 'uname -d'
+# https://github.com/att/ast/pull/1187
+builtin uname
+exp=$(uname -o)
+
+# Test for a possible crash (to avoid crashing the script, fork the subshell)
+(
+	ulimit -t unlimited
+	uname -d > /dev/null
+) || err_exit "'uname -d' crashes"
+
+# 'uname -d' shouldn't change the output of 'uname -o'
+got=$(ulimit -t unlimited; uname -d > /dev/null; uname -o)
+[[ $exp == $got ]] || err_exit "'uname -d' changes the output of 'uname -o'" \
+	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+
 # ======
 exit $((Errors<125?Errors:125))

src/lib/libcmd/uname.c

@@ -493,11 +493,14 @@ b_uname(int argc, char** argv, Shbltin_t* context)
 		if (flags & OPT_domain)
 		{
 			if (!*(s = astconf("SRPC_DOMAIN", NiL, NiL)))
+			{
 #if _lib_getdomainname
-				getdomainname(s, sizeof(buf));
+				getdomainname(buf, sizeof(buf));
+				s = buf;
 #else
 				/*NOP*/;
 #endif
+			}
 			output(OPT_domain, s, "domain");
 		}
 #if _mem_m_type_utsname