[bug#30826] [PATCH] gnu: shadow: Fix CVE-2018-7169.

[Leo Famulari <leo@famulari.name>]

* gnu/packages/patches/shadow-CVE-2018-7169.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/admin.scm (shadow)[source]: Use it.
---
 gnu/local.mk                                    |   1 +
 gnu/packages/admin.scm                          |   1 +
 gnu/packages/patches/shadow-CVE-2018-7169.patch | 191 ++++++++++++++++++++++++
 3 files changed, 193 insertions(+)
 create mode 100644 gnu/packages/patches/shadow-CVE-2018-7169.patch

diff --git a/gnu/local.mk b/gnu/local.mk
index 165b83067..69e4d2b7b 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -1082,6 +1082,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/scotch-test-threading.patch		\
   %D%/packages/patches/sdl-libx11-1.6.patch			\
   %D%/packages/patches/seq24-rename-mutex.patch			\
+  %D%/packages/patches/shadow-CVE-2018-7169.patch		\
   %D%/packages/patches/shepherd-close-fds.patch			\
   %D%/packages/patches/shepherd-herd-status-sorted.patch	\
   %D%/packages/patches/shishi-fix-libgcrypt-detection.patch	\
diff --git a/gnu/packages/admin.scm b/gnu/packages/admin.scm
index ad31bc498..d6f4a5fab 100644
--- a/gnu/packages/admin.scm
+++ b/gnu/packages/admin.scm
@@ -360,6 +360,7 @@ hostname.")
               (uri (string-append
                     "https://github.com/shadow-maint/shadow/releases/"
                     "download/" version "/shadow-" version ".tar.xz"))
+              (patches (search-patches "shadow-CVE-2018-7169.patch"))
               (sha256
                (base32
                 "0hdpai78n63l3v3fgr3kkiqzhd0awrpfnnzz4mf7lmxdh61qb37w"))))
diff --git a/gnu/packages/patches/shadow-CVE-2018-7169.patch b/gnu/packages/patches/shadow-CVE-2018-7169.patch
new file mode 100644
index 000000000..eeae5b9b7
--- /dev/null
+++ b/gnu/packages/patches/shadow-CVE-2018-7169.patch
@@ -0,0 +1,191 @@
+Fix CVE-2018-7169:
+
+https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-7169
+
+Patch copied from upstream source repository:
+
+https://github.com/shadow-maint/shadow/commit/fb28c99b8a66ff2605c5cb96abc0a4d975f92de0
+
+From fb28c99b8a66ff2605c5cb96abc0a4d975f92de0 Mon Sep 17 00:00:00 2001
+From: Aleksa Sarai <asarai@suse.de>
+Date: Thu, 15 Feb 2018 23:49:40 +1100
+Subject: [PATCH] newgidmap: enforce setgroups=deny if self-mapping a group
+
+This is necessary to match the kernel-side policy of "self-mapping in a
+user namespace is fine, but you cannot drop groups" -- a policy that was
+created in order to stop user namespaces from allowing trivial privilege
+escalation by dropping supplementary groups that were "blacklisted" from
+certain paths.
+
+This is the simplest fix for the underlying issue, and effectively makes
+it so that unless a user has a valid mapping set in /etc/subgid (which
+only administrators can modify) -- and they are currently trying to use
+that mapping -- then /proc/$pid/setgroups will be set to deny. This
+workaround is only partial, because ideally it should be possible to set
+an "allow_setgroups" or "deny_setgroups" flag in /etc/subgid to allow
+administrators to further restrict newgidmap(1).
+
+We also don't write anything in the "allow" case because "allow" is the
+default, and users may have already written "deny" even if they
+technically are allowed to use setgroups. And we don't write anything if
+the setgroups policy is already "deny".
+
+Ref: https://bugs.launchpad.net/ubuntu/+source/shadow/+bug/1729357
+Fixes: CVE-2018-7169
+Reported-by: Craig Furman <craig.furman89@gmail.com>
+Signed-off-by: Aleksa Sarai <asarai@suse.de>
+---
+ src/newgidmap.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++------
+ 1 file changed, 80 insertions(+), 9 deletions(-)
+
+diff --git a/src/newgidmap.c b/src/newgidmap.c
+index b1e33513..59a2e75c 100644
+--- a/src/newgidmap.c
++++ b/src/newgidmap.c
+@@ -46,32 +46,37 @@
+  */
+ const char *Prog;
+ 
+-static bool verify_range(struct passwd *pw, struct map_range *range)
++
++static bool verify_range(struct passwd *pw, struct map_range *range, bool *allow_setgroups)
+ {
+ 	/* An empty range is invalid */
+ 	if (range->count == 0)
+ 		return false;
+ 
+-	/* Test /etc/subgid */
+-	if (have_sub_gids(pw->pw_name, range->lower, range->count))
++	/* Test /etc/subgid. If the mapping is valid then we allow setgroups. */
++	if (have_sub_gids(pw->pw_name, range->lower, range->count)) {
++		*allow_setgroups = true;
+ 		return true;
++	}
+ 
+-	/* Allow a process to map its own gid */
+-	if ((range->count == 1) && (pw->pw_gid == range->lower))
++	/* Allow a process to map its own gid. */
++	if ((range->count == 1) && (pw->pw_gid == range->lower)) {
++		/* noop -- if setgroups is enabled already we won't disable it. */
+ 		return true;
++	}
+ 
+ 	return false;
+ }
+ 
+ static void verify_ranges(struct passwd *pw, int ranges,
+-	struct map_range *mappings)
++	struct map_range *mappings, bool *allow_setgroups)
+ {
+ 	struct map_range *mapping;
+ 	int idx;
+ 
+ 	mapping = mappings;
+ 	for (idx = 0; idx < ranges; idx++, mapping++) {
+-		if (!verify_range(pw, mapping)) {
++		if (!verify_range(pw, mapping, allow_setgroups)) {
+ 			fprintf(stderr, _( "%s: gid range [%lu-%lu) -> [%lu-%lu) not allowed\n"),
+ 				Prog,
+ 				mapping->upper,
+@@ -89,6 +94,70 @@ static void usage(void)
+ 	exit(EXIT_FAILURE);
+ }
+ 
++void write_setgroups(int proc_dir_fd, bool allow_setgroups)
++{
++	int setgroups_fd;
++	char *policy, policy_buffer[4096];
++
++	/*
++	 * Default is "deny", and any "allow" will out-rank a "deny". We don't
++	 * forcefully write an "allow" here because the process we are writing
++	 * mappings for may have already set themselves to "deny" (and "allow"
++	 * is the default anyway). So allow_setgroups == true is a noop.
++	 */
++	policy = "deny\n";
++	if (allow_setgroups)
++		return;
++
++	setgroups_fd = openat(proc_dir_fd, "setgroups", O_RDWR|O_CLOEXEC);
++	if (setgroups_fd < 0) {
++		/*
++		 * If it's an ENOENT then we are on too old a kernel for the setgroups
++		 * code to exist. Emit a warning and bail on this.
++		 */
++		if (ENOENT == errno) {
++			fprintf(stderr, _("%s: kernel doesn't support setgroups restrictions\n"), Prog);
++			goto out;
++		}
++		fprintf(stderr, _("%s: couldn't open process setgroups: %s\n"),
++			Prog,
++			strerror(errno));
++		exit(EXIT_FAILURE);
++	}
++
++	/*
++	 * Check whether the policy is already what we want. /proc/self/setgroups
++	 * is write-once, so attempting to write after it's already written to will
++	 * fail.
++	 */
++	if (read(setgroups_fd, policy_buffer, sizeof(policy_buffer)) < 0) {
++		fprintf(stderr, _("%s: failed to read setgroups: %s\n"),
++			Prog,
++			strerror(errno));
++		exit(EXIT_FAILURE);
++	}
++	if (!strncmp(policy_buffer, policy, strlen(policy)))
++		goto out;
++
++	/* Write the policy. */
++	if (lseek(setgroups_fd, 0, SEEK_SET) < 0) {
++		fprintf(stderr, _("%s: failed to seek setgroups: %s\n"),
++			Prog,
++			strerror(errno));
++		exit(EXIT_FAILURE);
++	}
++	if (dprintf(setgroups_fd, "%s", policy) < 0) {
++		fprintf(stderr, _("%s: failed to setgroups %s policy: %s\n"),
++			Prog,
++			policy,
++			strerror(errno));
++		exit(EXIT_FAILURE);
++	}
++
++out:
++	close(setgroups_fd);
++}
++
+ /*
+  * newgidmap - Set the gid_map for the specified process
+  */
+@@ -103,6 +172,7 @@ int main(int argc, char **argv)
+ 	struct stat st;
+ 	struct passwd *pw;
+ 	int written;
++	bool allow_setgroups = false;
+ 
+ 	Prog = Basename (argv[0]);
+ 
+@@ -145,7 +215,7 @@ int main(int argc, char **argv)
+ 				(unsigned long) getuid ()));
+ 		return EXIT_FAILURE;
+ 	}
+-	
++
+ 	/* Get the effective uid and effective gid of the target process */
+ 	if (fstat(proc_dir_fd, &st) < 0) {
+ 		fprintf(stderr, _("%s: Could not stat directory for target %u\n"),
+@@ -177,8 +247,9 @@ int main(int argc, char **argv)
+ 	if (!mappings)
+ 		usage();
+ 
+-	verify_ranges(pw, ranges, mappings);
++	verify_ranges(pw, ranges, mappings, &allow_setgroups);
+ 
++	write_setgroups(proc_dir_fd, allow_setgroups);
+ 	write_mapping(proc_dir_fd, ranges, mappings, "gid_map");
+ 	sub_gid_close();
+ 
+-- 
+2.16.2
+
-- 
2.16.2