From patchwork Thu Feb 15 21:12:17 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Martin KaFai Lau X-Patchwork-Id: 13559151 X-Patchwork-Delegate: bpf@iogearbox.net Received: from out-174.mta1.migadu.com (out-174.mta1.migadu.com [95.215.58.174]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 661CA135A66 for ; Thu, 15 Feb 2024 21:12:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.174 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708031560; cv=none; b=qoeucrAAvO+7xniA6nBvyJimGdw5AD28v24v6XFk/MMYRWAZdX02EcMH2ZMxb1fic3+af0+bB2ebBG5lL2c2dUeWaul94S9PZ5wIsi4ZKL4C85MQ+z/0HgOfUSpHX/+1MYTdT8o98LGjfjvk/Z+gjJwneUGbmQdExnzV0Z0MrP0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708031560; c=relaxed/simple; bh=WnQlAUoPaOq0riWFICNCJZ2GacqZG+XDDVp2SNa9Nnw=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=GDT4fIUFw1vyCEf5pC3Rg8dint/Ra1f4wzrqay25vH6M2pMkQeqPQMBeaNzB/NK5pHSqlAr7CXJxgtgMgoScx02/HYk4AbQCA6X2oxOIJvVM63hqPPB12+vNmI+jqk+hpMSV1SGbERxgvhzx3f1YabpZQ06hxdunYIaEzVd318Y= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=JbOCsCZt; arc=none smtp.client-ip=95.215.58.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="JbOCsCZt" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1708031556; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=4xQU1NAHNvLSXv9fJK/aKOfTnBei6Bpc3D8TitP0rFY=; b=JbOCsCZtlBSRHcOC2Wb0Lcfm7Kv+5sNIuLAXfgpacPs1EHE0Mri1ddY4rdFXHvzTasip4S gFV0jT5C1Q0Mv85dOS5nPvU3JR77ufpI48ep5dcLn+N2HwIhz2VLeQTKxefrRllaEeZon/ Xl2d0omG2y2AP2yoR0NGujSmmQoOfy8= From: Martin KaFai Lau To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , kernel-team@meta.com Subject: [PATCH bpf 1/2] bpf: Fix racing between bpf_timer_cancel_and_free and bpf_timer_cancel Date: Thu, 15 Feb 2024 13:12:17 -0800 Message-Id: <20240215211218.990808-1-martin.lau@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT X-Patchwork-Delegate: bpf@iogearbox.net From: Martin KaFai Lau The following race is possible between bpf_timer_cancel_and_free and bpf_timer_cancel. It will lead a UAF on the timer->timer. bpf_timer_cancel(); spin_lock(); t = timer->time; spin_unlock(); bpf_timer_cancel_and_free(); spin_lock(); t = timer->timer; timer->timer = NULL; spin_unlock(); hrtimer_cancel(&t->timer); kfree(t); /* UAF on t */ hrtimer_cancel(&t->timer); In bpf_timer_cancel_and_free, this patch frees the timer->timer after a rcu grace period. This requires a rcu_head addition to the "struct bpf_hrtimer". Another kfree(t) happens in bpf_timer_init, this does not need a kfree_rcu because it is still under the spin_lock and timer->timer has not been visible by others yet. In bpf_timer_cancel, rcu_read_lock() is added because this helper can be used in a non rcu critical section context (e.g. from a sleepable bpf prog). Other timer->timer usages in helpers.c have been audited, bpf_timer_cancel() is the only place where timer->timer is used outside of the spin_lock. Another solution considered is to mark a t->flag in bpf_timer_cancel and clear it after hrtimer_cancel() is done. In bpf_timer_cancel_and_free, it busy waits for the flag to be cleared before kfree(t). This patch goes with a straight forward solution and frees timer->timer after a rcu grace period. Fixes: b00628b1c7d5 ("bpf: Introduce bpf timers.") Suggested-by: Alexei Starovoitov Signed-off-by: Martin KaFai Lau Acked-by: Hou Tao --- kernel/bpf/helpers.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index be72824f32b2..d19cd863d294 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -1101,6 +1101,7 @@ struct bpf_hrtimer { struct bpf_prog *prog; void __rcu *callback_fn; void *value; + struct rcu_head rcu; }; /* the actual struct hidden inside uapi struct bpf_timer */ @@ -1332,6 +1333,7 @@ BPF_CALL_1(bpf_timer_cancel, struct bpf_timer_kern *, timer) if (in_nmi()) return -EOPNOTSUPP; + rcu_read_lock(); __bpf_spin_lock_irqsave(&timer->lock); t = timer->timer; if (!t) { @@ -1353,6 +1355,7 @@ BPF_CALL_1(bpf_timer_cancel, struct bpf_timer_kern *, timer) * if it was running. */ ret = ret ?: hrtimer_cancel(&t->timer); + rcu_read_unlock(); return ret; } @@ -1407,7 +1410,7 @@ void bpf_timer_cancel_and_free(void *val) */ if (this_cpu_read(hrtimer_running) != t) hrtimer_cancel(&t->timer); - kfree(t); + kfree_rcu(t, rcu); } BPF_CALL_2(bpf_kptr_xchg, void *, map_value, void *, ptr)