From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 9FC56606A332 for ; Mon, 26 Oct 2026 21:53:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20251104 header.b=ne/rp042 Received: by kanga.kvack.org (Postfix) id 35A6E6B05B9; Mon, 26 Oct 2026 17:52:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2E4516B05BA; Mon, 26 Oct 2026 17:52:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 137926B05BB; Mon, 26 Oct 2026 17:52:58 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id D77D36B05B9 for ; Mon, 26 Oct 2026 17:52:57 -0400 (EDT) Received: from smtpin11.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id E3AE1A843C for ; Mon, 26 Oct 2026 21:52:56 +0000 (UTC) X-FDA: 85366127952.11.91F3ABF Received: from mail-pj1-f70.google.com (mail-pj1-f70.google.com [209.85.216.70]) by imf02.hostedemail.com (Postfix) with ESMTP id 4488180004 for ; Mon, 26 Oct 2026 21:52:55 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=google.com header.s=20251104 header.b="ne/rp042"; spf=pass (imf02.hostedemail.com: domain of 3tcvfagoKCCoPZNUaMNZUTMUUMRK.IUSROTad-SSQbGIQ.UXM@flex--jthoughton.bounces.google.com designates 209.85.216.70 as permitted sender) smtp.mailfrom=3tcvfagoKCCoPZNUaMNZUTMUUMRK.IUSROTad-SSQbGIQ.UXM@flex--jthoughton.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793051575; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=UPD1DyegWTB9pcC/MXMtMDXG2VZzMQeq5nacp4T1bXw=; b=Lb10nN2W+GNM299N70WJb3XV0UT38W5QZx8PRGG3ZFTW/bQAce3bxFSusGMqsn55/T7h8b MfEP9NhoqnfoIZj2kMiP3aMMT00tYxTzR2Dox/suHzNtNtFItykkAOKdUD6vpzARgwaSjx Tdl03XY8kF2X/Fz34wOFXwZ4CE/0H0I= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=google.com header.s=20251104 header.b="ne/rp042"; spf=pass (imf02.hostedemail.com: domain of 3tcvfagoKCCoPZNUaMNZUTMUUMRK.IUSROTad-SSQbGIQ.UXM@flex--jthoughton.bounces.google.com designates 209.85.216.70 as permitted sender) smtp.mailfrom=3tcvfagoKCCoPZNUaMNZUTMUUMRK.IUSROTad-SSQbGIQ.UXM@flex--jthoughton.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793051575; b=0KH8YRKuhKcbzmZ/BHYt2wUKOIt452FtTbr1w5qa+oEaqNnByNWZghRxIb/4tJakjZ/Ig6 x7SoYmPHwPT/lmo21IJBL6aeISLKkUxhoVYd3TAKb/I25huXQVM0nUV4bBBNxDLfh3h9Vr wSFavI4pEaOClzRzMR8/GH3Bv8NLjWk= Received: by mail-pj1-f70.google.com with SMTP id 98e67ed59e1d1-3aaf955db5fso5549287a91.0 for ; Mon, 26 Oct 2026 14:52:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1793051574; x=1793656374; darn=kvack.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=UPD1DyegWTB9pcC/MXMtMDXG2VZzMQeq5nacp4T1bXw=; b=ne/rp042/l5TVp6Fuc+LsWZU4yutTqen/3hkPs8iNz0BXYZyMVHxOzYhDSnEtp23xr VPzn0+r9cJgxvBORJXPONoN07P3Og83WpSTju9KpnLPts8LX4pOaCCotMCJ43psgZmo/ wy3Z6136dqCdSprAx3tDeU6cggw1lUE2NYDuN1dTWnt1RARQjar2f7tcBbgbFaw/VMVP h0u417qXowKJI5SbTnwU+EsJ745apWD29g5HqdDHQvATLypM/hdjFCpRq6eyzEO2iT39 ypHPPjDs26BuCgW1hpVP4T3HhEbF2r+61eAuvmXHO0IR+wZJ2abxT1Z4F9j3yCpsZEXQ JjeQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1793051574; x=1793656374; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=UPD1DyegWTB9pcC/MXMtMDXG2VZzMQeq5nacp4T1bXw=; b=zr00Dg+nzhTJ3ksZNlslmFjk5k8UVnUCkAVDKPDl+xbmHGK6OousTSqx2UtMKca1SH aFWqkz7HKfRWYTvwPko0Lkvw6TLwJhZi/3wf5uhnZi3WZ3lUpZW9sTJJO5TtpqPeyI2P waegCUHAWGesoM/42hN7uaKbNeb/iJQ+tL/KOny66b9KIMX7625ERn1a4S4BPVBu03Jw ozbgunp10HtJJXg2+0HhyaPCmmvDjDhn5vEfK3SiO/H/JnBcW+AdwO2Bg1+tjVwgHNyD xdcFEI4RzWIqtPpij49GXBT+NWRoivh7kaV0SGjzCBkxSCMgrAW6cEiSzVmnfu/64V/i mAGw== X-Forwarded-Encrypted: i=1; AKwUvBwJT36P70tYF7hy+yeYXBITDPEEZYFvhf57oZtpXxYaaNGUM4giPx6s/XpHiT8OzRO8ZrqpTPjwvQ==@kvack.org X-Gm-Message-State: AFq9FYL0dvchh86Enx1KrtwClA5/SEk2R2Izy7c3dTH+vCSxorrva9VU MPYf4tcpnn7CwJTWxeBrViRWUMVPWr6PuKol4uMdL1+HKKne9J1XNRu8HxpSQSvE7xe0zG5Whgj 93VsC8KpDNDCfPe3V4WwJ+g== X-Received: from pjyp7.prod.google.com ([2002:a17:90a:e707:b0:3ab:c373:bf62]) (user=jthoughton job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:3e4d:b0:3ac:403d:6232 with SMTP id 98e67ed59e1d1-3adeb120167mr6870324a91.55.1793051573802; Mon, 26 Oct 2026 14:52:53 -0700 (PDT) Date: Mon, 26 Oct 2026 21:52:23 +0000 In-Reply-To: <20261026215226.3713941-1-jthoughton@google.com> X-Archived-By: Mime-Version: 1.0 References: <20261026215226.3713941-1-jthoughton@google.com> X-Mailer: git-send-email 2.56.0.307.g5fe7bd680c-goog Message-ID: <20261026215226.3713941-8-jthoughton@google.com> Subject: [RFC PATCH 07/10] uaccess: Fail user nofault helpers quietly when current->mm is NULL From: James Houghton To: Andrew Morton , Alexander Viro Cc: Thomas Gleixner , Peter Zijlstra , Kees Cook , Arnd Bergmann , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Sean Christopherson , Paolo Bonzini , Jim Mattson , Jens Axboe , Pavel Begunkov , "James E.J. Bottomley" , "Martin K. Petersen" , David Sterba , Chris Mason , Alexei Starovoitov , Daniel Borkmann , John Fastabend , Josh Poimboeuf , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org, io-uring@vger.kernel.org, linux-scsi@vger.kernel.org, linux-btrfs@vger.kernel.org, bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, James Houghton Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 4488180004 X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: i7thgoen4b3r1phuxtt8u98s6pt8i3rn X-HE-Tag: 1793051575-468285 X-HE-Meta: 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 DlsmwdGX 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 The user nofault helpers (copy_{from,to}_user_nofault(), strncpy_from_user_nofault() and strnlen_user_nofault()) are meant to be callable from any context, e.g. from BPF programs, kprobes or perf, which may run on behalf of a kernel thread or of a task that has already gone through exit_mm(). In such a context, there is no user memory to access, and the right answer is simply to fail. Since the previous commit, the uaccess helpers they use warn when current->mm is NULL, e.g. bpf_probe_read_user_str() from a BPF program attached to a function called by a kernel thread would now trip the WARN_ON_ONCE() in strncpy_from_user(). Check for a NULL current->mm up front in these helpers, and fail without warning and without attempting the access. On x86, copy_from_user_nofault() was already refusing such accesses, as nmi_uaccess_okay() returns false when current->mm is not the loaded mm. For the same reason, make copy_to_user_iter_nofault() use should_fail_usercopy() directly, leaving the NULL mm check to copy_to_user_nofault(). Signed-off-by: James Houghton --- lib/iov_iter.c | 2 +- mm/maccess.c | 17 +++++++++++++++++ 2 files changed, 18 insertions(+), 1 deletion(-) diff --git a/lib/iov_iter.c b/lib/iov_iter.c index 3d6ecb50d778..21e2ccf1e8f2 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -33,7 +33,7 @@ size_t copy_to_user_iter_nofault(void __user *iter_to, size_t progress, { ssize_t res; - if (uaccess_should_fail()) + if (should_fail_usercopy()) return len; from += progress; diff --git a/mm/maccess.c b/mm/maccess.c index 486559d68858..678bb6165b39 100644 --- a/mm/maccess.c +++ b/mm/maccess.c @@ -121,6 +121,14 @@ long copy_from_user_nofault(void *dst, const void __user *src, size_t size) { long ret = -EFAULT; + /* + * The user nofault helpers may be called from any context, including + * from tasks that have no user memory to access (e.g. kernel threads). + * Fail quietly instead of tripping the warning in the uaccess helpers. + */ + if (!current->mm) + return ret; + if (!__access_ok(src, size)) return ret; @@ -150,6 +158,9 @@ long copy_to_user_nofault(void __user *dst, const void *src, size_t size) { long ret = -EFAULT; + if (!current->mm) + return ret; + if (access_ok(dst, size)) { pagefault_disable(); ret = __copy_to_user_inatomic(dst, src, size); @@ -188,6 +199,9 @@ long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr, if (unlikely(count <= 0)) return 0; + if (!current->mm) + return -EFAULT; + pagefault_disable(); ret = strncpy_from_user(dst, unsafe_addr, count); pagefault_enable(); @@ -222,6 +236,9 @@ long strnlen_user_nofault(const void __user *unsafe_addr, long count) { int ret; + if (!current->mm) + return 0; + pagefault_disable(); ret = strnlen_user(unsafe_addr, count); pagefault_enable(); -- 2.56.0.307.g5fe7bd680c-goog