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From 01593d3299a1cfdb5e08acf95f63ec59dd674906 Mon Sep 17 00:00:00 2001
From: Stephen Smalley <sds@tycho.nsa.gov>
Date: Mon, 9 Jan 2017 10:07:31 -0500
Subject: [PATCH] selinux: allow context mounts on tmpfs, ramfs, devpts within
user namespaces
commit aad82892af261b9903cc11c55be3ecf5f0b0b4f8 ("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>
---
security/selinux/hooks.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index e4b953f..e32f4b5 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -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;
--
2.9.3
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