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 C683A335BA3; Mon, 18 Aug 2025 13:27:16 +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=1755523636; cv=none; b=NcjbgOsGhZGIyekLRblD+fs/s1xThx40RjSE5MPuDfg/4wkvqP8XWL+D8CxRJUtqOsvP8uHPXFm2h8UguIALcO0VyKwQWxs6jgGJpi27nQ8g+UtSlspzqBbobAx2aSYvlJpaGVnjeSh4zfRMOpicBIcTIwetaCpJqXTjG+IvQ/0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755523636; c=relaxed/simple; bh=CWZqlD6dHS2Bw2h7lLMfEX49jZs4MCCcHbJKUyhBhK8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tPXZZyiFTCi23PHgytF21m4CZI2A6PYGaE4WHuQCTuDWQ+pEZjHzAYDRwOeQIqLiTk5Ta8TPcsh/ZAP3ZecHpjvObQNP9/KUIZxax2mZo41p4wnfYMi7d9BqoPbkQqgtD8lFw3ZgD+1LVEsGnkNjX4JuqlEiB2aXH55RHgUmNgc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Jvr7opi2; 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="Jvr7opi2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4B7FFC4CEEB; Mon, 18 Aug 2025 13:27:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1755523636; bh=CWZqlD6dHS2Bw2h7lLMfEX49jZs4MCCcHbJKUyhBhK8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Jvr7opi2HST8kmnHwvKAURD+vs6W7qwGNiI6ETcczUKyHWyjXw6e2niAtVxvXcAEr bV5QPkr5Ypi0Q85t2WP34qGL5keaJOtCelZRI9r6mECCG2sW70wacymiMyWYjoHgUx Jbua0AABpCrrf1Kim6bhd8QUUAXpdvm7bO0AtV38= 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 6.15 233/515] bpf: Forget ranges when refining tnum after JSET Date: Mon, 18 Aug 2025 14:43:39 +0200 Message-ID: <20250818124507.347750641@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250818124458.334548733@linuxfoundation.org> References: <20250818124458.334548733@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 6.15-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 a1ecad2944a8..bdeed2a24910 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -16014,6 +16014,10 @@ 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