From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 0F03A54BD4; Tue, 27 Feb 2024 13:59:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709042394; cv=none; b=HmCONVfTd9caa/Ug20aUt1CiC5034Rn8ThE2BJke8hf+Vsxm9Jp33DvMlukBFL3b0DaI89Wv70ES2XaamDFoPgttnXM1KS23/UW6k4ZyYPcqi27O4oP/oNP362Pl5+7SFxUvqLxA0oYxcuciCTrqLMTifvgFTcxq4+u1zf8AdEk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709042394; c=relaxed/simple; bh=oBL6ImcBnrjVJWebeeDJgNW0Kd5pwMj5Y7QTr83xnk4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=kS+1E4p5tggb7HDTHtHm+VcXU0CvIfTh4GuLGpoaHRyxdJkjfWtg3t+/BZsVpj6qiwye2/jqDFoOxZMM3uRB1hfQeA/1xzqgyOVydfRgGmvB8yLYnrOXXp8Op1nORZ9klSWQAisYIcgOgKD/UkpFkmnIGtrH62C3V8cSlD38q58= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=JVZYgnGN; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="JVZYgnGN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 47952C433F1; Tue, 27 Feb 2024 13:59:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1709042393; bh=oBL6ImcBnrjVJWebeeDJgNW0Kd5pwMj5Y7QTr83xnk4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=JVZYgnGNSN8sXK//lUkvT1bGtRSFG09bx4nkV0M2k2eOeLKtrHpP4aPLhisKVq8Mz F6j7iQqLJdU/MfUkmfN60tv2LvDtdnxwBSL+liB4aqILuNAZB2qtBbD6VEGXzII5MI OJKD5sKUtEbzkDvfzYpTT0ePWP58plsvNZ1pI2vI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Alexei Starovoitov , Martin KaFai Lau , Daniel Borkmann , Hou Tao , Sasha Levin Subject: [PATCH 6.6 252/299] bpf: Fix racing between bpf_timer_cancel_and_free and bpf_timer_cancel Date: Tue, 27 Feb 2024 14:26:03 +0100 Message-ID: <20240227131633.830677078@linuxfoundation.org> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240227131625.847743063@linuxfoundation.org> References: <20240227131625.847743063@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Martin KaFai Lau [ Upstream commit 0281b919e175bb9c3128bd3872ac2903e9436e3f ] 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 Signed-off-by: Daniel Borkmann Acked-by: Hou Tao Link: https://lore.kernel.org/bpf/20240215211218.990808-1-martin.lau@linux.dev Signed-off-by: Sasha Levin --- 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 e68ef39cda675..a5ce840f4fbef 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -1100,6 +1100,7 @@ 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 */ @@ -1328,6 +1329,7 @@ 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) { @@ -1349,6 +1351,7 @@ 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; } @@ -1403,7 +1406,7 @@ 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) -- 2.43.0