security: Add LSM hook to setgroups() syscall

Give the LSM framework the ability to filter setgroups() syscalls. There
are already analagous hooks for the set*uid() and set*gid() syscalls.
The SafeSetID LSM will use this new hook to ensure setgroups() calls are
allowed by the installed security policy. Tested by putting print
statement in security_task_fix_setgroups() hook and confirming that it
gets hit when userspace does a setgroups() syscall.

Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Micah Morton <mortonm@chromium.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/kernel/groups.c b/kernel/groups.c
index 787b381c7c00..9aaed2a31073 100644
--- a/kernel/groups.c
+++ b/kernel/groups.c
@@ -134,13 +134,26 @@ EXPORT_SYMBOL(set_groups);
 int set_current_groups(struct group_info *group_info)
 {
 	struct cred *new;
+	const struct cred *old;
+	int retval;
 
 	new = prepare_creds();
 	if (!new)
 		return -ENOMEM;
 
+	old = current_cred();
+
 	set_groups(new, group_info);
+
+	retval = security_task_fix_setgroups(new, old);
+	if (retval < 0)
+		goto error;
+
 	return commit_creds(new);
+
+error:
+	abort_creds(new);
+	return retval;
 }
 
 EXPORT_SYMBOL(set_current_groups);