linux-kernel - Re: SELinux change in 3.13 causes sync hang

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Message-ID: <1386707123.23829.23.camel@flatline.rdu.redhat.com>
Date:	Tue, 10 Dec 2013 15:25:23 -0500
From:	Eric Paris <eparis@...hat.com>
To:	Josh Boyer <jwboyer@...oraproject.org>
Cc:	Anand Avati <avati@...hat.com>, James Morris <jmorris@...ei.org>,
	Eric Sandeen <sandeen@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: SELinux change in 3.13 causes sync hang

I still believe (assuming Josh says it tests ok) that a revert is a
reasonable fix until next window.  But I might know the actual problem:

Lets assume policy says:
   fuse.gluster == use_xattr

Lets assume this function is called with
sb->s_type->name == fuse
sb->s_subtype == NULL

int security_fs_use(struct super_block *sb)
{
        int rc = 0;
        struct ocontext *c;
        struct superblock_security_struct *sbsec = sb->s_security;
        const char *fstype = sb->s_type->name;
        const char *subtype = (sb->s_subtype && sb->s_subtype[0]) ? sb->s_subtype : NULL;
        struct ocontext *base = NULL;

        read_lock(&policy_rwlock);

        for (c = policydb.ocontexts[OCON_FSUSE]; c; c = c->next) {
                char *sub;
                int baselen;

                baselen = strlen(fstype);

		**********  assume c == the above rule   name = fuse.gluster

                /* if base does not match, this is not the one */
                if (strncmp(fstype, c->u.name, baselen))    <----------- this will match
                        continue;

                /* if there is no subtype, this is the one! */
                if (!subtype)   <--------------------------------------- we will break here!
                        break;
[snip]
        }
[snip]
        if (c) {
                sbsec->behavior = c->v.behavior;

So we just matched on the fuse.gluster rule even though the mount in
question was fstype=fuse subtype=NULL     So we will try to use xattrs
on a fuse FS that can/will deadlock.

I'll try to write a patch to fix that logic...

-Eric

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