[PATCH nfs-utils v2 1/2] fsidd: call anonymous sockets by their name only, don't fill with NULs to 108 bytes

[Ahelenia Ziemiańska <nabijaczleweli@xxxxxxxxxxxxxxxxxx>]

Since e00ab3c0616fe6d83ab0710d9e7d989c299088f7, ss -l looks like this:
  u_seq               LISTEN                0                     5                                    @/run/fsid.sock@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 26989379                                                       * 0
with fsidd pushing all the addresses to 108 bytes wide, which is deeply
egregious if you don't filter it out and recolumnate.

This is because, naturally (unix(7)), "Null bytes in the name have
no special significance": abstract addresses are binary blobs, but
paths automatically terminate at the first NUL byte, since paths
can't contain those.

So just specify the correct address length when we're using the abstract domain:
unix(7) recommends "offsetof(struct sockaddr_un, sun_path) + strlen(sun_path) + 1"
for paths, but we don't want to include the terminating NUL, so it's just
"offsetof(struct sockaddr_un, sun_path) + strlen(sun_path)".
This brings the width back to order:
-- >8 --
$ ss -la | grep @
u_str ESTAB     0      0      @45208536ec96909a/bus/systemd-timesyn/bus-api-timesync 18500238                            * 18501249
u_str ESTAB     0      0       @fecc9657d2315eb7/bus/systemd-network/bus-api-network 18495452                            * 18494406
u_seq LISTEN    0      5                                             @/run/fsid.sock 27168796                            * 0
u_str ESTAB     0      0                 @ac308f35f50797a2/bus/systemd-logind/system 19406                               * 15153
u_str ESTAB     0      0                @b6606e0dfacbae75/bus/systemd/bus-api-system 18494353                            * 18495334
u_str ESTAB     0      0                    @5880653d215718a7/bus/systemd/bus-system 26930876                            * 26930003
-- >8 --

Fixes: e00ab3c0616fe6d83ab0710d9e7d989c299088f7 ("fsidd: provide
 better default socket name.")
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@xxxxxxxxxxxxxxxxxx>
---
v1: <04f3fe71defa757d518468f04f08334a5d0dfbb9.1693754442.git.nabijaczleweli@xxxxxxxxxxxxxxxxxx>
v2 NFC, addr_len declared at top of function

 support/reexport/fsidd.c    | 9 ++++++---
 support/reexport/reexport.c | 8 ++++++--
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/support/reexport/fsidd.c b/support/reexport/fsidd.c
index 3e62b3fc..8a70b78f 100644
--- a/support/reexport/fsidd.c
+++ b/support/reexport/fsidd.c
@@ -147,6 +147,7 @@ int main(void)
 {
 	struct event *srv_ev;
 	struct sockaddr_un addr;
+	socklen_t addr_len;
 	char *sock_file;
 	int srv;
 
@@ -161,10 +162,12 @@ int main(void)
 	memset(&addr, 0, sizeof(struct sockaddr_un));
 	addr.sun_family = AF_UNIX;
 	strncpy(addr.sun_path, sock_file, sizeof(addr.sun_path) - 1);
-	if (addr.sun_path[0] == '@')
+	addr_len = sizeof(struct sockaddr_un);
+	if (addr.sun_path[0] == '@') {
 		/* "abstract" socket namespace */
+		addr_len = offsetof(struct sockaddr_un, sun_path) + strlen(addr.sun_path);
 		addr.sun_path[0] = 0;
-	else
+	} else
 		unlink(sock_file);
 
 	srv = socket(AF_UNIX, SOCK_SEQPACKET | SOCK_NONBLOCK, 0);
@@ -173,7 +176,7 @@ int main(void)
 		return 1;
 	}
 
-	if (bind(srv, (const struct sockaddr *)&addr, sizeof(struct sockaddr_un)) == -1) {
+	if (bind(srv, (const struct sockaddr *)&addr, addr_len) == -1) {
 		xlog(L_WARNING, "Unable to bind %s: %m\n", sock_file);
 		return 1;
 	}
diff --git a/support/reexport/reexport.c b/support/reexport/reexport.c
index 78516586..0fb49a46 100644
--- a/support/reexport/reexport.c
+++ b/support/reexport/reexport.c
@@ -21,6 +21,7 @@ static int fsidd_srv = -1;
 static bool connect_fsid_service(void)
 {
 	struct sockaddr_un addr;
+	socklen_t addr_len;
 	char *sock_file;
 	int ret;
 	int s;
@@ -33,9 +34,12 @@ static bool connect_fsid_service(void)
 	memset(&addr, 0, sizeof(struct sockaddr_un));
 	addr.sun_family = AF_UNIX;
 	strncpy(addr.sun_path, sock_file, sizeof(addr.sun_path) - 1);
-	if (addr.sun_path[0] == '@')
+	addr_len = sizeof(struct sockaddr_un);
+	if (addr.sun_path[0] == '@') {
 		/* "abstract" socket namespace */
+		addr_len = offsetof(struct sockaddr_un, sun_path) + strlen(addr.sun_path);
 		addr.sun_path[0] = 0;
+	}
 
 	s = socket(AF_UNIX, SOCK_SEQPACKET, 0);
 	if (s == -1) {
@@ -43,7 +47,7 @@ static bool connect_fsid_service(void)
 		return false;
 	}
 
-	ret = connect(s, (const struct sockaddr *)&addr, sizeof(struct sockaddr_un));
+	ret = connect(s, (const struct sockaddr *)&addr, addr_len);
 	if (ret == -1) {
 		xlog(L_WARNING, "Unable to connect %s: %m, is fsidd running?\n", sock_file);
 		return false;
-- 
2.39.2

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