gnu: shadow: Fix CVE-2018-7169.
* 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.
This commit is contained in:
Leo Famulari
parent
71f9ca53e5
commit
20ecede969
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@ -1082,6 +1082,7 @@ dist_patch_DATA = \
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%D%/packages/patches/scotch-test-threading.patch \
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%D%/packages/patches/sdl-libx11-1.6.patch \
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%D%/packages/patches/seq24-rename-mutex.patch \
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%D%/packages/patches/shadow-CVE-2018-7169.patch \
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%D%/packages/patches/shepherd-close-fds.patch \
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%D%/packages/patches/shepherd-herd-status-sorted.patch \
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%D%/packages/patches/shishi-fix-libgcrypt-detection.patch \
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@ -360,6 +360,7 @@ hostname.")
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(uri (string-append
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"https://github.com/shadow-maint/shadow/releases/"
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"download/" version "/shadow-" version ".tar.xz"))
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(patches (search-patches "shadow-CVE-2018-7169.patch"))
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(sha256
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(base32
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"0hdpai78n63l3v3fgr3kkiqzhd0awrpfnnzz4mf7lmxdh61qb37w"))))
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@ -0,0 +1,191 @@
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Fix CVE-2018-7169:
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https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-7169
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Patch copied from upstream source repository:
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https://github.com/shadow-maint/shadow/commit/fb28c99b8a66ff2605c5cb96abc0a4d975f92de0
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From fb28c99b8a66ff2605c5cb96abc0a4d975f92de0 Mon Sep 17 00:00:00 2001
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From: Aleksa Sarai <asarai@suse.de>
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Date: Thu, 15 Feb 2018 23:49:40 +1100
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Subject: [PATCH] newgidmap: enforce setgroups=deny if self-mapping a group
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This is necessary to match the kernel-side policy of "self-mapping in a
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user namespace is fine, but you cannot drop groups" -- a policy that was
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created in order to stop user namespaces from allowing trivial privilege
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escalation by dropping supplementary groups that were "blacklisted" from
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certain paths.
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This is the simplest fix for the underlying issue, and effectively makes
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it so that unless a user has a valid mapping set in /etc/subgid (which
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only administrators can modify) -- and they are currently trying to use
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that mapping -- then /proc/$pid/setgroups will be set to deny. This
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workaround is only partial, because ideally it should be possible to set
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an "allow_setgroups" or "deny_setgroups" flag in /etc/subgid to allow
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administrators to further restrict newgidmap(1).
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We also don't write anything in the "allow" case because "allow" is the
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default, and users may have already written "deny" even if they
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technically are allowed to use setgroups. And we don't write anything if
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the setgroups policy is already "deny".
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Ref: https://bugs.launchpad.net/ubuntu/+source/shadow/+bug/1729357
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Fixes: CVE-2018-7169
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Reported-by: Craig Furman <craig.furman89@gmail.com>
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Signed-off-by: Aleksa Sarai <asarai@suse.de>
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---
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src/newgidmap.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++------
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1 file changed, 80 insertions(+), 9 deletions(-)
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diff --git a/src/newgidmap.c b/src/newgidmap.c
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index b1e33513..59a2e75c 100644
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--- a/src/newgidmap.c
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+++ b/src/newgidmap.c
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@@ -46,32 +46,37 @@
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*/
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const char *Prog;
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-static bool verify_range(struct passwd *pw, struct map_range *range)
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+
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+static bool verify_range(struct passwd *pw, struct map_range *range, bool *allow_setgroups)
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{
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/* An empty range is invalid */
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if (range->count == 0)
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return false;
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- /* Test /etc/subgid */
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- if (have_sub_gids(pw->pw_name, range->lower, range->count))
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+ /* Test /etc/subgid. If the mapping is valid then we allow setgroups. */
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+ if (have_sub_gids(pw->pw_name, range->lower, range->count)) {
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+ *allow_setgroups = true;
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return true;
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+ }
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- /* Allow a process to map its own gid */
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- if ((range->count == 1) && (pw->pw_gid == range->lower))
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+ /* Allow a process to map its own gid. */
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+ if ((range->count == 1) && (pw->pw_gid == range->lower)) {
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+ /* noop -- if setgroups is enabled already we won't disable it. */
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return true;
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+ }
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return false;
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}
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static void verify_ranges(struct passwd *pw, int ranges,
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- struct map_range *mappings)
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+ struct map_range *mappings, bool *allow_setgroups)
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{
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struct map_range *mapping;
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int idx;
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mapping = mappings;
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for (idx = 0; idx < ranges; idx++, mapping++) {
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- if (!verify_range(pw, mapping)) {
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+ if (!verify_range(pw, mapping, allow_setgroups)) {
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fprintf(stderr, _( "%s: gid range [%lu-%lu) -> [%lu-%lu) not allowed\n"),
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Prog,
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mapping->upper,
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@@ -89,6 +94,70 @@ static void usage(void)
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exit(EXIT_FAILURE);
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}
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+void write_setgroups(int proc_dir_fd, bool allow_setgroups)
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+{
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+ int setgroups_fd;
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+ char *policy, policy_buffer[4096];
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+
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+ /*
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+ * Default is "deny", and any "allow" will out-rank a "deny". We don't
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+ * forcefully write an "allow" here because the process we are writing
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+ * mappings for may have already set themselves to "deny" (and "allow"
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+ * is the default anyway). So allow_setgroups == true is a noop.
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+ */
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+ policy = "deny\n";
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+ if (allow_setgroups)
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+ return;
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+
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+ setgroups_fd = openat(proc_dir_fd, "setgroups", O_RDWR|O_CLOEXEC);
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+ if (setgroups_fd < 0) {
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+ /*
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+ * If it's an ENOENT then we are on too old a kernel for the setgroups
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+ * code to exist. Emit a warning and bail on this.
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+ */
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+ if (ENOENT == errno) {
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+ fprintf(stderr, _("%s: kernel doesn't support setgroups restrictions\n"), Prog);
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+ goto out;
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+ }
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+ fprintf(stderr, _("%s: couldn't open process setgroups: %s\n"),
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+ Prog,
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+ strerror(errno));
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+ exit(EXIT_FAILURE);
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+ }
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+
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+ /*
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+ * Check whether the policy is already what we want. /proc/self/setgroups
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+ * is write-once, so attempting to write after it's already written to will
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+ * fail.
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+ */
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+ if (read(setgroups_fd, policy_buffer, sizeof(policy_buffer)) < 0) {
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+ fprintf(stderr, _("%s: failed to read setgroups: %s\n"),
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+ Prog,
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+ strerror(errno));
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+ exit(EXIT_FAILURE);
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+ }
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+ if (!strncmp(policy_buffer, policy, strlen(policy)))
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+ goto out;
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+
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+ /* Write the policy. */
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+ if (lseek(setgroups_fd, 0, SEEK_SET) < 0) {
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+ fprintf(stderr, _("%s: failed to seek setgroups: %s\n"),
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+ Prog,
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+ strerror(errno));
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+ exit(EXIT_FAILURE);
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+ }
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+ if (dprintf(setgroups_fd, "%s", policy) < 0) {
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+ fprintf(stderr, _("%s: failed to setgroups %s policy: %s\n"),
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+ Prog,
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+ policy,
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+ strerror(errno));
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+ exit(EXIT_FAILURE);
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+ }
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+
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+out:
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+ close(setgroups_fd);
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+}
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+
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/*
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* newgidmap - Set the gid_map for the specified process
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*/
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@@ -103,6 +172,7 @@ int main(int argc, char **argv)
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struct stat st;
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struct passwd *pw;
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int written;
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+ bool allow_setgroups = false;
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Prog = Basename (argv[0]);
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@@ -145,7 +215,7 @@ int main(int argc, char **argv)
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(unsigned long) getuid ()));
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return EXIT_FAILURE;
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}
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-
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+
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/* Get the effective uid and effective gid of the target process */
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if (fstat(proc_dir_fd, &st) < 0) {
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fprintf(stderr, _("%s: Could not stat directory for target %u\n"),
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@@ -177,8 +247,9 @@ int main(int argc, char **argv)
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if (!mappings)
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usage();
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- verify_ranges(pw, ranges, mappings);
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+ verify_ranges(pw, ranges, mappings, &allow_setgroups);
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+ write_setgroups(proc_dir_fd, allow_setgroups);
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write_mapping(proc_dir_fd, ranges, mappings, "gid_map");
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sub_gid_close();
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--
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2.16.2
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