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From 4a49d45dd58994f4fc9b40c502252403caadee88 Mon Sep 17 00:00:00 2001
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From: Stephen Smalley <sds@tycho.nsa.gov>
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Date: Thu, 8 Dec 2016 09:14:47 -0500
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Subject: [PATCH] selinux: allow context mounts on tmpfs, ramfs, devpts within
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user namespaces
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commit aad82892af261b9903cc11c55be3ecf5f0b0b4f8 ("selinux: Add support for
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unprivileged mounts from user namespaces") prohibited any use of context
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mount options within non-init user namespaces. However, this breaks
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use of context mount options for tmpfs mounts within user namespaces,
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which are being used by Docker/runc. There is no reason to block such
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usage for tmpfs, ramfs or devpts. Exempt these filesystem types
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from this restriction.
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Before:
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sh$ userns_child_exec -p -m -U -M '0 1000 1' -G '0 1000 1' bash
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sh# mount -t tmpfs -o context=system_u:object_r:user_tmp_t:s0:c13 none /tmp
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mount: tmpfs is write-protected, mounting read-only
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mount: cannot mount tmpfs read-only
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After:
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sh$ userns_child_exec -p -m -U -M '0 1000 1' -G '0 1000 1' bash
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sh# mount -t tmpfs -o context=system_u:object_r:user_tmp_t:s0:c13 none /tmp
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sh# ls -Zd /tmp
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unconfined_u:object_r:user_tmp_t:s0:c13 /tmp
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Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
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Signed-off-by: Paul Moore <paul@paul-moore.com>
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---
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security/selinux/hooks.c | 10 +++++++---
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1 file changed, 7 insertions(+), 3 deletions(-)
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diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
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index b508a5a..e7c5481 100644
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--- a/security/selinux/hooks.c
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+++ b/security/selinux/hooks.c
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@@ -834,10 +834,14 @@ static int selinux_set_mnt_opts(struct super_block *sb,
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}
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/*
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- * If this is a user namespace mount, no contexts are allowed
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- * on the command line and security labels must be ignored.
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+ * If this is a user namespace mount and the filesystem type is not
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+ * explicitly whitelisted, then no contexts are allowed on the command
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+ * line and security labels must be ignored.
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*/
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- if (sb->s_user_ns != &init_user_ns) {
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+ if (sb->s_user_ns != &init_user_ns &&
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+ strcmp(sb->s_type->name, "tmpfs") &&
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+ strcmp(sb->s_type->name, "ramfs") &&
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+ strcmp(sb->s_type->name, "devpts")) {
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if (context_sid || fscontext_sid || rootcontext_sid ||
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defcontext_sid) {
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rc = -EACCES;
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--
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2.4.11
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