From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 63E393B27DB for ; Mon, 27 Jul 2026 15:41:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785166868; cv=none; b=JzJVRx1JyPjFZlnWx5Zc83ledKCT60eO3dRnQLqaEfOzuTJ6yDm2rvM/onbBpEzyO9LS9AncNClSzS25loKhYB7u6qWEHzQNBmrRqjlUDYzF0QAkrfAMvfjW0lYTSkSLZ8R5rg/jRdvWj36hOhuwUIuCl/F71VUYsw6nstJY/AA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785166868; c=relaxed/simple; bh=aLdebKuqpPjYyiXqING6Kshh+B61ZgePmcotJBZ75GY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=mUHh61Fq0dFo+hIJLmMf/SjHIw2j/lVAeVQgJgZQhdw/e6/6w7M0HMJ4G8Vfsf7h1CCftiq+6IsnU5pzrK7QlwEtz3Mys1y2igq1QhdE/Yv+Yt3qy0gAk9S4hz6Uzx/nT0TvYpG/wo+wFs80Jqt8Nc2X7kF0FzT859pi/ertHU4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eVSd9pIF; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="eVSd9pIF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7BB541F00A3A; Mon, 27 Jul 2026 15:41:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785166867; bh=dMHu5FZRUYJfyOt2A9g+6xGqjXFHc12zfGiobjTFjO4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=eVSd9pIFZYMlWeJzWDMjrK71gQ2kIzJZmKtUrrmllzekNyyMcKBZDpiPvjOyrVFLe wd1CJibScggthzn9OS0cMyr6n60IvtL9QYSFFPuIPRgEMGVjepTJCOZMX2IcdjIa55 VIKr0Fa2qAWprvLdvEZm52LOyCvQnAX41DY3jtaGki7LH4YGGTnq+v1f9pudgcj/nt Y0tXgiv4bZC1EKEl0j0BnCjp+qnPo5Tu0xits+r1rKfpGDOYyzN1ivfVsR/ML/IvbA hb/2L2SgjUS4hlmXcZ5FVyRKjwlP7R3RxaKlZQdIEeGlDjto85OSaVkrN+HIQ2nwDG LPBXLQOflq5Sg== From: Sasha Levin To: stable@vger.kernel.org Cc: Tristan Madani , Eduard Zingerman , Alexei Starovoitov , Sasha Levin Subject: [PATCH 6.12.y 3/3] bpf: Reset register bounds before narrowing retval range in check_mem_access() Date: Mon, 27 Jul 2026 11:41:03 -0400 Message-ID: <20260727154103.1515347-3-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260727154103.1515347-1-sashal@kernel.org> References: <2026072011-poach-marina-ef6e@gregkh> <20260727154103.1515347-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tristan Madani [ Upstream commit 5e0b273e0a62cc04ec338c7b502797c66c2ed42a ] When the BPF verifier processes a context load of an LSM hook return value, it calls __mark_reg_s32_range() to narrow the register to the hook's valid range. However, __mark_reg_s32_range() intersects the new range with the register's existing bounds using max_t()/min_t() rather than replacing them. If the destination register carries stale bounds from a prior instruction (e.g. BPF_MOV64_IMM), the intersection can produce a range narrower than reality. The verifier then believes it knows the register's exact value, while at runtime the actual hook return value is loaded, creating a verifier/runtime mismatch that can be used to bypass BPF memory safety checks. The else branch already calls mark_reg_unknown() to reset register state before any narrowing. Apply the same reset in the is_retval path so stale bounds are cleared before __mark_reg_s32_range() intersects. Fixes: 5d99e198be27 ("bpf, lsm: Add check for BPF LSM return value") Cc: stable@vger.kernel.org Signed-off-by: Tristan Madani Acked-by: Eduard Zingerman Link: https://lore.kernel.org/r/20260622230123.3695446-2-tristmd@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- kernel/bpf/verifier.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 373e6a2326946e..38436a2708e564 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -7219,6 +7219,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn */ if (info.reg_type == SCALAR_VALUE) { if (info.is_retval && get_func_retval_range(env->prog, &range)) { + mark_reg_unknown(env, regs, value_regno); err = __mark_reg_s32_range(env, regs, value_regno, range.minval, range.maxval); if (err) -- 2.53.0