[PATCH 0/2] pasta: Do not configure ID mappings when invoked with --netns-only

[PATCH 0/2] pasta: Do not configure ID mappings when invoked with --netns-only

[Dwayne B. Bent]

This is a narrow fix for bug 216 where `pasta` attempts to configure
user and group ID mappings when invoked with `--netns-only`. A new
`bool` argument `config_idmaps` was added to `pasta_start_ns()` that
guards the logic to configure user and group ID mappings. It is set to
`false` when `netns_only` is `true`.

OpenAI Codex was used to explore and understand the codebase. Code
written myself. Test written by Codex guided and reviewed by me.


Dwayne B. Bent (2):
  pasta: Regression test for bug 216
  pasta: Do not configure ID mappings when invoked with --netns-only

 conf.c                        |  2 +-
 pasta.c                       | 24 ++++++++++++++----------
 pasta.h                       |  3 ++-
 test/pasta_options/netns_only | 19 +++++++++++++++++++
 test/run                      |  1 +
 5 files changed, 37 insertions(+), 12 deletions(-)
 create mode 100644 test/pasta_options/netns_only

-- 
2.55.0

[PATCH 1/2] pasta: Regression test for bug 216

[Dwayne B. Bent]

Adds a test that asserts that when pasta is invoked via `unshare -r` in
standalone mode with `--netns-only` it does not print any warnings, and
the command executes successfully.

Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Dwayne B. Bent <dbb@dbb.dev>
---
 test/pasta_options/netns_only | 19 +++++++++++++++++++
 test/run                      |  1 +
 2 files changed, 20 insertions(+)
 create mode 100644 test/pasta_options/netns_only

diff --git a/test/pasta_options/netns_only b/test/pasta_options/netns_only
new file mode 100644
index 0000000..197ed44
--- /dev/null
+++ b/test/pasta_options/netns_only
@@ -0,0 +1,19 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+#
+# PASST - Plug A Simple Socket Transport
+#  for qemu/UNIX domain socket mode
+#
+# PASTA - Pack A Subtle Tap Abstraction
+#  for network namespace/tap device mode
+#
+# test/pasta_options/netns_only - Check --netns-only handling
+
+htools	unshare grep
+
+test	--netns-only skips id mapping configuration
+set	OUT __STATEDIR__/netns-only.out
+set	ERR __STATEDIR__/netns-only.err
+
+passt	unshare -r -- ./pasta -q --netns-only -- echo TEST > __OUT__ 2> __ERR__
+check	grep -qx TEST __OUT__
+check	[ ! -s __ERR__ ]
diff --git a/test/run b/test/run
index f858e55..c4073cc 100755
--- a/test/run
+++ b/test/run
@@ -85,6 +85,7 @@ run() {
 
 	setup pasta_options
 	test pasta_options/log_to_file
+	test pasta_options/netns_only
 	teardown pasta_options
 
 	setup build
-- 
2.55.0

[PATCH 2/2] pasta: Do not configure ID mappings when invoked with --netns-only

[Dwayne B. Bent]

Add a `bool` argument `config_idmaps` to `pasta_start_ns()` that guards
the logic to configure user and group ID mappings. It is set to `false`
when `netns_only` is `true`. Fixes bug 216.

Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Dwayne B. Bent <dbb@dbb.dev>
---
 conf.c  |  2 +-
 pasta.c | 24 ++++++++++++++----------
 pasta.h |  3 ++-
 3 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/conf.c b/conf.c
index 0fcba5c..2223604 100644
--- a/conf.c
+++ b/conf.c
@@ -1945,7 +1945,7 @@ void conf(struct ctx *c, int argc, char **argv)
 		if (*netns) {
 			pasta_open_ns(c, netns);
 		} else {
-			pasta_start_ns(c, uid, gid,
+			pasta_start_ns(c, uid, gid, !netns_only,
 				       argc - optind, argv + optind);
 		}
 	}
diff --git a/pasta.c b/pasta.c
index 4e7ee54..5aa56b7 100644
--- a/pasta.c
+++ b/pasta.c
@@ -236,10 +236,11 @@ static int pasta_spawn_cmd(void *arg)
  * @c:		Execution context
  * @uid:	UID we're running as in the init namespace
  * @gid:	GID we're running as in the init namespace
+ * @config_idmaps:	Whether to configure user mappings
  * @argc:	Number of arguments for spawned command
  * @argv:	Command to spawn and arguments
  */
-void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid,
+void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid, bool config_idmaps,
 		    int argc, char *argv[])
 {
 	char ns_fn_stack[NS_FN_STACK_SIZE]
@@ -249,7 +250,6 @@ void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid,
 		.argv = argv,
 		.c = c,
 	};
-	char uidmap[BUFSIZ], gidmap[BUFSIZ];
 	char *sh_argv[] = { NULL, NULL };
 	char sh_arg0[PATH_MAX + 1];
 	sigset_t set;
@@ -259,16 +259,20 @@ void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid,
 		c->quiet = 1;
 
 	/* Configure user and group mappings */
-	if (snprintf_check(uidmap, BUFSIZ, "0 %u 1", uid))
-		die_perror("Can't build uidmap");
+	if (config_idmaps) {
+		char uidmap[BUFSIZ], gidmap[BUFSIZ];
 
-	if (snprintf_check(gidmap, BUFSIZ, "0 %u 1", gid))
-		die_perror("Can't build gidmap");
+		if (snprintf_check(uidmap, BUFSIZ, "0 %u 1", uid))
+			die_perror("Can't build uidmap");
 
-	if (write_file("/proc/self/uid_map", uidmap) ||
-	    write_file("/proc/self/setgroups", "deny") ||
-	    write_file("/proc/self/gid_map", gidmap)) {
-		warn("Couldn't configure user mappings");
+		if (snprintf_check(gidmap, BUFSIZ, "0 %u 1", gid))
+			die_perror("Can't build gidmap");
+
+		if (write_file("/proc/self/uid_map", uidmap) ||
+		    write_file("/proc/self/setgroups", "deny") ||
+		    write_file("/proc/self/gid_map", gidmap)) {
+			warn("Couldn't configure user mappings");
+		}
 	}
 
 	if (argc == 0) {
diff --git a/pasta.h b/pasta.h
index 07e04b3..edd7747 100644
--- a/pasta.h
+++ b/pasta.h
@@ -6,12 +6,13 @@
 #ifndef PASTA_H
 #define PASTA_H
 
+#include <stdbool.h>
 #include <unistd.h>
 
 extern int pasta_child_pid;
 
 void pasta_open_ns(struct ctx *c, const char *netns);
-void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid,
+void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid, bool config_idmaps,
 		    int argc, char *argv[]);
 void pasta_ns_conf(struct ctx *c);
 void pasta_child_handler(int signal);
-- 
2.55.0