From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: [PATCH v6 21/26] fs: Handle intra-page faults in copy_mount_options() Date: Fri, 3 Jul 2020 16:37:13 +0100 Message-ID: <20200703153718.16973-22-catalin.marinas@arm.com> References: <20200703153718.16973-1-catalin.marinas@arm.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: Received: from mail.kernel.org ([198.145.29.99]:41698 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726147AbgGCPiN (ORCPT ); Fri, 3 Jul 2020 11:38:13 -0400 In-Reply-To: <20200703153718.16973-1-catalin.marinas@arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: linux-arm-kernel@lists.infradead.org Cc: linux-mm@kvack.org, linux-arch@vger.kernel.org, Will Deacon , Dave P Martin , Vincenzo Frascino , Szabolcs Nagy , Kevin Brodsky , Andrey Konovalov , Peter Collingbourne , Andrew Morton , Alexander Viro The copy_mount_options() function takes a user pointer argument but no size and it tries to read up to a PAGE_SIZE. However, copy_from_user() is not guaranteed to return all the accessible bytes if, for example, the access crosses a page boundary and gets a fault on the second page. To work around this, the current copy_mount_options() implementation performs two copy_from_user() passes, first to the end of the current page and the second to what's left in the subsequent page. On arm64 with MTE enabled, access to a user page may trigger a fault after part of the buffer in a page has been copied (when the user pointer tag, bits 56-59, no longer matches the allocation tag stored in memory). Allow copy_mount_options() to handle such intra-page faults by resorting to byte at a time copy in case of copy_from_user() failure. Note that copy_from_user() handles the zeroing of the kernel buffer in case of error. Signed-off-by: Catalin Marinas Cc: Alexander Viro --- Notes: v6: - Simplified logic to fall-back to byte-by-byte if the copy_from_user() fails. v4: - Rewrite to avoid arch_has_exact_copy_from_user() New in v3. fs/namespace.c | 25 ++++++++++++++++++------- 1 file changed, 18 insertions(+), 7 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index f30ed401cc6d..163ac986dc2d 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -3074,7 +3074,7 @@ static void shrink_submounts(struct mount *mnt) void *copy_mount_options(const void __user * data) { char *copy; - unsigned size; + unsigned left, offset; if (!data) return NULL; @@ -3083,16 +3083,27 @@ void *copy_mount_options(const void __user * data) if (!copy) return ERR_PTR(-ENOMEM); - size = PAGE_SIZE - offset_in_page(data); + left = copy_from_user(copy, data, PAGE_SIZE); - if (copy_from_user(copy, data, size)) { + /* + * Not all architectures have an exact copy_form_user(). Resort to + * byte at a time. + */ + offset = PAGE_SIZE - left; + while (left) { + char c; + if (get_user(c, (const char __user *)data + offset)) + break; + copy[offset] = c; + left--; + offset++; + } + + if (left == PAGE_SIZE) { kfree(copy); return ERR_PTR(-EFAULT); } - if (size != PAGE_SIZE) { - if (copy_from_user(copy + size, data + size, PAGE_SIZE - size)) - memset(copy + size, 0, PAGE_SIZE - size); - } + return copy; }