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 CEF0A531AFE for ; Wed, 16 Sep 2026 18:33:10 +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=1789583598; cv=none; b=OtNgf3gjyBTip9lQ1JT16un9G5RTZU3bVP/N2SbUeuS0cWnFGhR6gn7dw6499pFM38xFySLaEi+BPmHStEp03pop9saKRidd+K3R+Omlh10HeBLCTu3hnJjhRsOSGVRQWrgg8oHoClRzUz4AoUhYy7Ra7eA87gWjWxhLe71vvYs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789583598; c=relaxed/simple; bh=7bZ+CD7MxU7KyaS2HcKIEJd5GKcxRooEie8Av6bWjK0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=dYLg3sBgYm8kt+JKv0D+bQu6Ge/GdMxZqH6xleHt8f5bVoeHxlJDG9I7XdwuX5Ta5a67SGy7CSP3N7uEghqBOaeiy3QCy6h8bxxkkL7fcU1r8AbcfMdg33MYFfRZ2FMruor+YDOXu8ko7UM/ypNaKxGhqDV/SV+BAbK32BFXSCo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=i4TOxlxQ; 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="i4TOxlxQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 619071F0089E; Wed, 16 Sep 2026 18:33:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789583586; bh=avwd/pLizCblJy1+dOq4I9WvHtAxM0pHrDvv48z6tWQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=i4TOxlxQ8y+6qW18LmieJFFUshTJPiH+GDV1rOTzL77aLlnuBeDvkDSn+t78enP8b nTl2zz3lJuLYQOhZKx2qygZ5C8fG/0hXAxgbGRND2Rn/m6bHSfr4gxsyD4XLkGR+Ne urPkYDM1L+hBBLTAt+GWxY4Y3RmvUEaz1iWLBrgxT888j+qpQBNox5CrhjRjo970k7 pDCn0EKbaxSL+PEm5dXbii72KdKg2b+9QpTrrHCOkpE8NBGmz8tNd0t1kcbljuOQGE 4xQLhgMnFF9ZP0ECMzI1O2F4G5W3kW7qLGLc1BnFF16/dBZ3Vf+U0zFEDSGdbODI7K dmj1VlRgZ9s5Q== From: Chris Mason To: mason@kernel.org, bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, brauner@kernel.org Subject: [PATCH RFC 1/2] bpf: fix UAF via trusted BTF walk after release Date: Wed, 16 Sep 2026 18:33:02 +0000 Message-ID: <20260916183303.3504885-2-mason@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260916183303.3504885-1-mason@kernel.org> References: <20260916183303.3504885-1-mason@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit A BPF program can keep dereferencing a trusted pointer that it loaded from a referenced object after it has released that reference. With a file from bpf_get_task_exe_file(), f->f_inode stays usable after bpf_put_file(), and loads through it read freed or reused inode memory. A pointer derived from a referenced object is only valid while the reference is held. release_reference() enforces that by invalidating every register whose id or parent_id matches the released id. However, check_ptr_to_btf_access() builds the loaded register with mark_btf_ld_reg(), which is not given the source register and zeroes both fields. The verifier state for the f_inode case: file = bpf_get_task_exe_file(task) file: id=N, referenced inode = file->f_inode inode: trusted, id=0, parent_id=0 bpf_put_file(file) release_reference(N) skips inode inode->i_ino accepted, unprobed load Reproduced by reading inode->i_ino after bpf_put_file() once the task owning the file had exited and new fds were created. Fix this by recording the source's reference id in the parent_id of a trusted PTR_TO_BTF_ID load. A program that dereferences such a pointer after the release is now rejected with "invalid mem access 'scalar'". Assisted-by: kres Fixes: 57539b1c0ac2 ("bpf: Enable annotating trusted nested pointers") Signed-off-by: Chris Mason --- kernel/bpf/verifier.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 6c6b8d8520cd..8b48bf796823 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6219,9 +6219,25 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env, } if (atype == BPF_READ && value_regno >= 0) { + u32 link_id = 0; + + /* + * A trusted pointer walked from a referenced object is only + * valid while that reference is held. Remember the reference + * id of the source, or the one it inherited, so that + * release_reference() invalidates the loaded register too. + * Read it now, reg may alias regs[value_regno]. + */ + if (ret == PTR_TO_BTF_ID && (flag & PTR_TRUSTED)) + link_id = reg_is_referenced(env, reg) ? reg->id : reg->parent_id; + ret = mark_btf_ld_reg(env, regs, value_regno, ret, reg->btf, btf_id, flag); if (ret < 0) return ret; + + /* mark_btf_ld_reg() cleared parent_id, set it afterwards. */ + if (link_id) + regs[value_regno].parent_id = link_id; } return 0; -- 2.54.0