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selinux: Add support for unprivileged mounts from user namespaces 

Security labels from unprivileged mounts in user namespaces must
be ignored. Force superblocks from user namespaces whose labeling
behavior is to use xattrs to use mountpoint labeling instead.
For the mountpoint label, default to converting the current task
context into a form suitable for file objects, but also allow the
policy writer to specify a different label through policy
transition rules.

Pieced together from code snippets provided by Stephen Smalley.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Seth Forshee 2016-04-26 14:36:20 -05:00 committed by Eric W. Biederman
parent 809c02e091
commit aad82892af
1 changed files with 23 additions and 0 deletions
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23
security/selinux/hooks.c
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@ -830,6 +830,28 @@ static int selinux_set_mnt_opts(struct super_block *sb,
goto out;
}
}
/*
* If this is a user namespace mount, no contexts are allowed
* on the command line and security labels must be ignored.
*/
if (sb->s_user_ns != &init_user_ns) {
if (context_sid || fscontext_sid || rootcontext_sid ||
defcontext_sid) {
rc = -EACCES;
goto out;
}
if (sbsec->behavior == SECURITY_FS_USE_XATTR) {
sbsec->behavior = SECURITY_FS_USE_MNTPOINT;
rc = security_transition_sid(current_sid(), current_sid(),
SECCLASS_FILE, NULL,
&sbsec->mntpoint_sid);
if (rc)
goto out;
}
goto out_set_opts;
}
/* sets the context of the superblock for the fs being mounted. */
if (fscontext_sid) {
rc = may_context_mount_sb_relabel(fscontext_sid, sbsec, cred);
@ -898,6 +920,7 @@ static int selinux_set_mnt_opts(struct super_block *sb,
sbsec->def_sid = defcontext_sid;
}
out_set_opts:
rc = sb_finish_set_opts(sb);
out:
mutex_unlock(&sbsec->lock);