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SubjectRe: apparmor: WARNING: suspicious RCU usage
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On 9/21/21 1:32 AM, Thomas Gleixner wrote:
>
> 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 Thomas, I look into it

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