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 42DE113C8E8; Mon, 18 Aug 2025 13:56:31 +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=1755525391; cv=none; b=Tt1dbZKk5Yim2Jwjz4Y6E0vdcp0qNzAcjea/WbQl4LaZAbRr8W06dkbSj+ca8YiKeyG3sKNyC7TFzjtt+a+trYVRRSv72yJd+GzAOOqKxIBk9TXbLbYuK5pYLkvGhSXPNO9MafIHWihiUuCzha6zKaltBU7TdFLgLvIxEhHKNKM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755525391; c=relaxed/simple; bh=D4eFwirA7D8VIfjR49OqxRtqaWZ2VWfxiGjbHaPJvE4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=i1/4tobiDJiwlD8A8AiIeykgugtU475vMprhWRmjD2nytpmXgxgFn5w4Rv0OrmqgOfa+pfZJfwyprGkcuNZMOshCvK0uPq4fdM5lZlNGsKYhBweuE7t1VgiOuF0xEKUp3MDHTKFfmvLNysdALPuC+WXcpOorEIAiENTqZyyeIiI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=czHqnlka; 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="czHqnlka" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B5015C4CEEB; Mon, 18 Aug 2025 13:56:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1755525391; bh=D4eFwirA7D8VIfjR49OqxRtqaWZ2VWfxiGjbHaPJvE4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=czHqnlkaC2aXFOH61i/jQNiKq3QpIM7CU1TGXTAckqB+aCscp2BCH54IbkcXaqwKR qeFc0bIXXLyLXch6JLCYM5ptlpPYYlmb0tc4kr3uUMhmngG8a+5GE/LYBUsNpyFW28 ldrlyP7uxd3zVCUrgpk0gEpbTyvXI9w2q6hFT6aI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+c711ce17dd78e5d4fdcf@syzkaller.appspotmail.com, Eduard Zingerman , Yonghong Song , Paul Chaignon , Alexei Starovoitov , Sasha Levin Subject: [PATCH 6.16 249/570] bpf: Forget ranges when refining tnum after JSET Date: Mon, 18 Aug 2025 14:43:56 +0200 Message-ID: <20250818124515.412655187@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250818124505.781598737@linuxfoundation.org> References: <20250818124505.781598737@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.16-stable review patch. If anyone has any objections, please let me know. ------------------ From: Paul Chaignon [ Upstream commit 6279846b9b2532e1b04559ef8bd0dec049f29383 ] Syzbot reported a kernel warning due to a range invariant violation on the following BPF program. 0: call bpf_get_netns_cookie 1: if r0 == 0 goto 2: if r0 & Oxffffffff goto The issue is on the path where we fall through both jumps. That path is unreachable at runtime: after insn 1, we know r0 != 0, but with the sign extension on the jset, we would only fallthrough insn 2 if r0 == 0. Unfortunately, is_branch_taken() isn't currently able to figure this out, so the verifier walks all branches. The verifier then refines the register bounds using the second condition and we end up with inconsistent bounds on this unreachable path: 1: if r0 == 0 goto r0: u64=[0x1, 0xffffffffffffffff] var_off=(0, 0xffffffffffffffff) 2: if r0 & 0xffffffff goto r0 before reg_bounds_sync: u64=[0x1, 0xffffffffffffffff] var_off=(0, 0) r0 after reg_bounds_sync: u64=[0x1, 0] var_off=(0, 0) Improving the range refinement for JSET to cover all cases is tricky. We also don't expect many users to rely on JSET given LLVM doesn't generate those instructions. So instead of improving the range refinement for JSETs, Eduard suggested we forget the ranges whenever we're narrowing tnums after a JSET. This patch implements that approach. Reported-by: syzbot+c711ce17dd78e5d4fdcf@syzkaller.appspotmail.com Suggested-by: Eduard Zingerman Acked-by: Yonghong Song Acked-by: Eduard Zingerman Signed-off-by: Paul Chaignon Link: https://lore.kernel.org/r/9d4fd6432a095d281f815770608fdcd16028ce0b.1752171365.git.paul.chaignon@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- kernel/bpf/verifier.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 97e07eb31fec..94ff01f1ab8a 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -16028,6 +16028,10 @@ static void regs_refine_cond_op(struct bpf_reg_state *reg1, struct bpf_reg_state if (!is_reg_const(reg2, is_jmp32)) break; val = reg_const_value(reg2, is_jmp32); + /* Forget the ranges before narrowing tnums, to avoid invariant + * violations if we're on a dead branch. + */ + __mark_reg_unbounded(reg1); if (is_jmp32) { t = tnum_and(tnum_subreg(reg1->var_off), tnum_const(~val)); reg1->var_off = tnum_with_subreg(reg1->var_off, t); -- 2.39.5