39a706fbcf
Avoiding taking a lock in an IRQ context is not enough to prevent deadlocks, as discovered by syzbot: === WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected 5.5.0-syzkaller #0 Not tainted ----------------------------------------------------- syz-executor.0/8927 [HC0[0]:SC0[2]:HE1:SE0] is trying to acquire: ffff888027c94098 (&(&s->cache_lock)->rlock){+.+.}, at: spin_lock include/linux/spinlock.h:338 [inline] ffff888027c94098 (&(&s->cache_lock)->rlock){+.+.}, at: sidtab_sid2str_put.part.0+0x36/0x880 security/selinux/ss/sidtab.c:533 and this task is already holding: ffffffff898639b0 (&(&nf_conntrack_locks[i])->rlock){+.-.}, at: spin_lock include/linux/spinlock.h:338 [inline] ffffffff898639b0 (&(&nf_conntrack_locks[i])->rlock){+.-.}, at: nf_conntrack_lock+0x17/0x70 net/netfilter/nf_conntrack_core.c:91 which would create a new lock dependency: (&(&nf_conntrack_locks[i])->rlock){+.-.} -> (&(&s->cache_lock)->rlock){+.+.} but this new dependency connects a SOFTIRQ-irq-safe lock: (&(&nf_conntrack_locks[i])->rlock){+.-.} [...] other info that might help us debug this: Possible interrupt unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&(&s->cache_lock)->rlock); local_irq_disable(); lock(&(&nf_conntrack_locks[i])->rlock); lock(&(&s->cache_lock)->rlock); <Interrupt> lock(&(&nf_conntrack_locks[i])->rlock); *** DEADLOCK *** [...] === Fix this by simply locking with irqsave/irqrestore and stop giving up on !in_task(). It makes the locking a bit slower, but it shouldn't make a big difference in real workloads. Under the scenario from [1] (only cache hits) it only increased the runtime overhead from the security_secid_to_secctx() function from ~2% to ~3% (it was ~5-65% before introducing the cache). [1] https://bugzilla.redhat.com/show_bug.cgi?id=1733259 Fixes: d97bd23c2d7d ("selinux: cache the SID -> context string translation") Reported-by: syzbot+61cba5033e2072d61806@syzkaller.appspotmail.com Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com> Acked-by: Stephen Smalley <sds@tycho.nsa.gov> Signed-off-by: Paul Moore <paul@paul-moore.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.