From: Thomas Gleixner <tglx@linutronix.de>
To: John Johansen <john.johansen@canonical.com>
Cc: James Morris <jmorris@namei.org>,
LSM List <linux-security-module@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: apparmor: WARNING: suspicious RCU usage
Date: Tue, 21 Sep 2021 10:32:37 +0200 [thread overview]
Message-ID: <877dfa72hm.ffs@tglx> (raw)
Running with CONFIG_PROVE_RCU_LIST triggers the following splat:
[ 6.805926] =============================
[ 6.806848] WARNING: suspicious RCU usage
[ 6.807738] 5.15.0-rc2+ #24 Tainted: G E
[ 6.808860] -----------------------------
[ 6.809734] security/apparmor/include/lib.h:191 RCU-list traversed in non-reader section!!
[ 6.811508]
other info that might help us debug this:
[ 6.811516]
rcu_scheduler_active = 2, debug_locks = 1
[ 6.811527] 2 locks held by apparmor_parser/1897:
[ 6.811530] #0: ffff88885f139450 (sb_writers#7){.+.+}-{0:0}, at: ksys_write+0x68/0xe0
[ 6.816110] #1: ffff8881000578a0 (&ns->lock){+.+.}-{3:3}, at: aa_replace_profiles+0x16d/0x11e0
[ 6.817418]
stack backtrace:
[ 6.818086] CPU: 38 PID: 1897 Comm: apparmor_parser Tainted: G E 5.15.0-rc2+ #24
[ 6.819359] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
[ 6.820536] Call Trace:
[ 6.820918] dump_stack_lvl+0x57/0x72
[ 6.821499] __lookupn_profile+0x193/0x1a0
[ 6.822461] aa_replace_profiles+0x395/0x11e0
[ 6.823448] policy_update+0x13f/0x240
[ 6.824326] profile_replace+0xb1/0x120
[ 6.825213] vfs_write+0xe4/0x3b0
[ 6.826027] ksys_write+0x68/0xe0
[ 6.826576] do_syscall_64+0x3b/0x90
[ 6.827099] entry_SYSCALL_64_after_hwframe+0x44/0xae
which is pretty obvious because aa_replace_profile() invokes:
__lookup_replace()
__lookup_profile()
__strn_find_child()
__policy_strn_find()
list_for_each_entry_rcu() <- Splat
The code is "correct" as this is the writer side and holding ns->lock,
but it's incorrect to use list_for_each_entry_rcu() without being in a
read side critical section unless it is properly annotated.
Same problem in the same function vs. __lookup_parent() and there are
more issues of that sort, e.g. vs. __lookup_profile() in
aa_remove_profiles().
Thanks,
tglx
next reply other threads:[~2021-09-21 8:32 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-21 8:32 Thomas Gleixner [this message]
2021-09-21 21:23 ` apparmor: WARNING: suspicious RCU usage John Johansen
2025-07-05 15:47 ` Breno Leitao
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