wildcards in file_contexts.subs for NixOS

[Russell Coker <russell.coker@daisee.com>]

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https://nixos.org/

The NixOS distribution of Linux is based on having hashes of packages in the 
path names.

/nix/store/l2b7y9waqwp4i1f03899yfsmzk8i7rid-shadow-4.5/bin/usermod
/nix/store/l2b7y9waqwp4i1f03899yfsmzk8i7rid-shadow-4.5/bin/vipw
/nix/store/lvrxkcf4b398nyiayknsqr44p8pl51s9-drbd-8.4.4/bin/drbdadm
/nix/store/lvrxkcf4b398nyiayknsqr44p8pl51s9-drbd-8.4.4/bin/drbdsetup
/nix/store/mzxhj1cxrhbqvsga4155xhw44iigwxxs-shadow-4.5-su/bin/su
/nix/store/n3d4l234fppvz40jjyqlxa1jxglzbs48-xen-4.8.2/bin/xenconsoled
/nix/store/n3d4l234fppvz40jjyqlxa1jxglzbs48-xen-4.8.2/bin/xenstored
/nix/store/n3d4l234fppvz40jjyqlxa1jxglzbs48-xen-4.8.2/bin/xl
/nix/store/n419slr5x6h4ydk2dd56nkwki7qpkf6v-fuse-2.9.7/bin/fusermount
/nix/store/n419slr5x6h4ydk2dd56nkwki7qpkf6v-fuse-2.9.7/bin/mount.fuse
/nix/store/pc4j7b2bvac49qmjllhw9rk0fnbr86fs-libvirt-3.10.0/bin/libvirtd
/nix/store/pc4j7b2bvac49qmjllhw9rk0fnbr86fs-libvirt-3.10.0/bin/virsh
/nix/store/pc4j7b2bvac49qmjllhw9rk0fnbr86fs-libvirt-3.10.0/bin/virtlockd
/nix/store/pc4j7b2bvac49qmjllhw9rk0fnbr86fs-libvirt-3.10.0/bin/virtlogd
/nix/store/pr94n9l1kvpiqilhjr308xbr8qmzilih-extra-utils/bin/blkid
/nix/store/pr94n9l1kvpiqilhjr308xbr8qmzilih-extra-utils/bin/dmsetup
/nix/store/pr94n9l1kvpiqilhjr308xbr8qmzilih-extra-utils/bin/e2fsck

Above is a random sample of binaries that need labelling on a NixOS system.  
Before anyone asks, the naming of such paths is core to the way NixOS works, 
requesting a change in that regard is not viable.

NixOS can run as a full OS (managing grub etc) or it can run on a system 
running a regular Linux distribution.  Running as a full OS or as a labelled 
chroot are the use cases that interest me.

semanage fcontext -a -e / "/nix/store/*"

setfiles -r /chroot/nix /etc/selinux/default/contexts/files/file_contexts \
/chroot/nix/store -v

I've written a patch to support commands like the above to label a Nix store 
(the above is a chroot example but the next step is to get full SE Linux 
support in NixOS).

I've attached the patch.  I don't expect this version to be accepted upstream 
as-is.  But it's a place to start the discussion about how to approach this 
problem.

Russell Coker

PS Please use my personal address russell@coker.com.au for SE Linux 
discussions unrelated to NixOS.

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[-- Type: text/x-patch; name="wildcard-subs.diff", Size: 2017 bytes --]

Description: Support wildcard source (EG /lib/*) in file_contexts.subs_dist

Index: libselinux-2.8/src/label_file.c
===================================================================
--- libselinux-2.8.orig/src/label_file.c
+++ libselinux-2.8/src/label_file.c
@@ -581,6 +581,25 @@ static char *selabel_sub(struct selabel_
 
 	while (ptr) {
 		if (strncmp(src, ptr->src, ptr->slen) == 0 ) {
+			if (ptr->wildcard)
+			{
+				if ( src[ptr->slen] == 0 || !strchr(src+ptr->slen, '/') )
+				{
+					ptr = ptr->next;
+					continue;
+				}
+				for(len = ptr->slen + 1 ; src[len] && src[len] != '/' ; len++)
+					;
+				if(!src[len])
+				{
+					ptr = ptr->next;
+					continue;
+				}
+				len++;
+				if (asprintf(&dst, "%s%s", ptr->dst, &src[len]) < 0)
+					return NULL;
+				return dst;
+			}
 			if (src[ptr->slen] == '/' ||
 			    src[ptr->slen] == 0) {
 				if ((src[ptr->slen] == '/') &&
@@ -606,6 +625,7 @@ static int selabel_subs_init(const char
 	struct selabel_sub *list = NULL, *sub = NULL;
 	struct stat sb;
 	int status = -1;
+	int len;
 
 	*out_subs = NULL;
 	if (!cfg) {
@@ -630,6 +650,8 @@ static int selabel_subs_init(const char
 		*ptr++ = '\0';
 		if (! *src) continue;
 
+		if(!strcmp("/*", src)) continue;
+
 		dst = ptr;
 		while (*dst && isspace(*dst))
 			dst++;
@@ -645,6 +667,16 @@ static int selabel_subs_init(const char
 			goto err;
 		memset(sub, 0, sizeof(*sub));
 
+		len = strlen(src);
+		if(len < 2) continue;
+		if(src[len - 1] == '*')
+		{
+			sub->wildcard = 1;
+			src[len - 1] = 0;
+			len--;
+		}
+		else
+			sub->wildcard = 0;
 		sub->src=strdup(src);
 		if (! sub->src)
 			goto err;
Index: libselinux-2.8/src/label_file.h
===================================================================
--- libselinux-2.8.orig/src/label_file.h
+++ libselinux-2.8/src/label_file.h
@@ -35,6 +35,7 @@ struct selabel_sub {
 	char *src;
 	int slen;
 	char *dst;
+	int wildcard;
 	struct selabel_sub *next;
 };