From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta0.migadu.com (out-174.mta0.migadu.com [91.218.175.174]) (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 B6CB02080C8 for ; Sun, 26 Oct 2025 16:38:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761496731; cv=none; b=KXJn96WbYtrKZh7eqiQ7Q//fjsCuGECqVXjEeaeBq94cX+4qmbVQJc3+S8t42AX+79s1UWoWtXxHF7+VB8+3pFXkLVHYkI/YFj2Aabns0aufvuA3n3ijfeifegT3aK22frSVZjQyVOb0aKl5ZS5uJ523uMJZxGZ07Q3apYXfN7M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761496731; c=relaxed/simple; bh=DEw7ZOeAhejnvjJ1BDBFz3PfQdtqnj7GFeIhTc3OuG0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=EeSts5ONfMRcLq9FajBqPKrZmqB5rLQINqE5jkLEgeReIQkeAOTKPIWwQH4smz9n28ilS1YeO1WOp3mHBdMFan6RhlHUKKs5EOJjdsx/Xqtg/gu/dxigkq5qjgzRw9pNdyJETTY2sDpQrB2gEhR2iPpjLqzai9dQcrPGrTFMLV8= 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=LzSQOpsJ; arc=none smtp.client-ip=91.218.175.174 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="LzSQOpsJ" 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=1761496727; 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: in-reply-to:in-reply-to:references:references; bh=HFoJR/u0IaB/0PpKtMKlYiR9B8oxdFtp8dSKC4xgXkY=; b=LzSQOpsJHn6rFsK+TfZWJOs4aaD/pVMhAHOY7TtByt2X/ef4VXy8Ycy/E2zHUZLDkEmcth wvzNb6T5mXqUyzqvrZAI6tPdjcqa09KbyDEoCvvcfZ07nZ0VqFzqa9i8GCrHdcepqmHzCg A77mM81A8q33C3GBRRAa0e/EGqhNbbI= From: KaFai Wan To: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, shuah@kernel.org, paul.chaignon@gmail.com, m.shachnai@gmail.com, memxor@gmail.com, harishankar.vishwanathan@gmail.com, colin.i.king@gmail.com, kafai.wan@linux.dev, luis.gerhorst@fau.de, shung-hsi.yu@suse.com, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: syzbot+c950cc277150935cc0b5@syzkaller.appspotmail.com Subject: [PATCH bpf-next 1/2] bpf: Fix tnum_overlap to check for zero mask first Date: Mon, 27 Oct 2025 00:38:05 +0800 Message-ID: <20251026163806.3300636-2-kafai.wan@linux.dev> In-Reply-To: <20251026163806.3300636-1-kafai.wan@linux.dev> References: <20251026163806.3300636-1-kafai.wan@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Syzbot reported a kernel warning due to a range invariant violation in the BPF verifier. The issue occurs when tnum_overlap() fails to detect that two tnums don't have any overlapping bits. The problematic BPF program: 0: call bpf_get_prandom_u32 1: r6 = r0 2: r6 &= 0xFFFFFFFFFFFFFFF0 3: r7 = r0 4: r7 &= 0x07 5: r7 -= 0xFF 6: if r6 == r7 goto After instruction 5, R7 has the range: R7: u64=[0xffffffffffffff01, 0xffffffffffffff08] var_off=(0xffffffffffffff00; 0xf) R6 and R7 don't overlap since they have no agreeing bits. However, is_branch_taken() fails to recognize this, causing the verifier to refine register bounds and end up with inconsistent bounds: 6: if r6 == r7 goto R6: u64=[0xffffffffffffff01, 0xffffffffffffff00] var_off=(0xffffffffffffff00, 0x0) R7: u64=[0xffffffffffffff01, 0xffffffffffffff00] var_off=(0xffffffffffffff00, 0x0) The root cause is that tnum_overlap() doesn't properly handle the case where the masks have no overlapping bits. Fix this by adding an early check for zero mask intersection in tnum_overlap(). Reported-by: syzbot+c950cc277150935cc0b5@syzkaller.appspotmail.com Fixes: f41345f47fb2 ("bpf: Use tnums for JEQ/JNE is_branch_taken logic") Signed-off-by: KaFai Wan --- kernel/bpf/tnum.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/bpf/tnum.c b/kernel/bpf/tnum.c index f8e70e9c3998..af2f38b4f840 100644 --- a/kernel/bpf/tnum.c +++ b/kernel/bpf/tnum.c @@ -163,6 +163,8 @@ bool tnum_overlap(struct tnum a, struct tnum b) { u64 mu; + if ((a.mask & b.mask) == 0) + return false; mu = ~a.mask & ~b.mask; return (a.value & mu) == (b.value & mu); } -- 2.43.0