Commit 01593d32 authored Jan 09, 2017 by Stephen Smalley Committed by Paul Moore Jan 09, 2017

selinux: allow context mounts on tmpfs, ramfs, devpts within user namespaces



commit aad82892 ("selinux: Add support for
unprivileged mounts from user namespaces") prohibited any use of context
mount options within non-init user namespaces.  However, this breaks
use of context mount options for tmpfs mounts within user namespaces,
which are being used by Docker/runc.  There is no reason to block such
usage for tmpfs, ramfs or devpts.  Exempt these filesystem types
from this restriction.

Before:
sh$ userns_child_exec  -p -m -U -M '0 1000 1' -G '0 1000 1' bash
sh# mount -t tmpfs -o context=system_u:object_r:user_tmp_t:s0:c13 none /tmp
mount: tmpfs is write-protected, mounting read-only
mount: cannot mount tmpfs read-only

After:
sh$ userns_child_exec  -p -m -U -M '0 1000 1' -G '0 1000 1' bash
sh# mount -t tmpfs -o context=system_u:object_r:user_tmp_t:s0:c13 none /tmp
sh# ls -Zd /tmp
unconfined_u:object_r:user_tmp_t:s0:c13 /tmp

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>

parent ef37979a

security/selinux/hooks.c

+7 −3

Original line number	Diff line number	Diff line
		@@ -834,10 +834,14 @@ static int selinux_set_mnt_opts(struct super_block *sb,
		}

		/*
		* If this is a user namespace mount, no contexts are allowed
		* on the command line and security labels must be ignored.
		* If this is a user namespace mount and the filesystem type is not
		* explicitly whitelisted, then no contexts are allowed on the command
		* line and security labels must be ignored.
		*/
		if (sb->s_user_ns != &init_user_ns) {
		if (sb->s_user_ns != &init_user_ns &&
		strcmp(sb->s_type->name, "tmpfs") &&
		strcmp(sb->s_type->name, "ramfs") &&
		strcmp(sb->s_type->name, "devpts")) {
		if (context_sid \|\| fscontext_sid \|\| rootcontext_sid \|\|
		defcontext_sid) {
		rc = -EACCES;

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