From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C606DC433E1 for ; Mon, 1 Jun 2020 20:07:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9911A20734 for ; Mon, 1 Jun 2020 20:07:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591042052; bh=WLG4kcqEt9VdTt2Je1rr3PBXsRXzaEOmL6iqofLYZlU=; h=From:To:Cc:Subject:Date:List-ID:From; b=jP06mN+duwvGW0fn3DPjy3jNDGD/4fKB0wgyLr7sffWJKKNRBiDrsXNgVsY6bJq6H U8+pu8M7JdvdBrdfmQqdhDd2c3/lTXxtqazfWoU75hHn8Hz25IjCs4rHc1SleQz9Ch P3TgyRrUbIgQnkNhHzyENV5IdXCekfz0HSA62ykc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728410AbgFAUHb (ORCPT ); Mon, 1 Jun 2020 16:07:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:46082 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726201AbgFAUHb (ORCPT ); Mon, 1 Jun 2020 16:07:31 -0400 Received: from sol.hsd1.ca.comcast.net (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 898D82074B; Mon, 1 Jun 2020 20:07:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591042050; bh=WLG4kcqEt9VdTt2Je1rr3PBXsRXzaEOmL6iqofLYZlU=; h=From:To:Cc:Subject:Date:From; b=U/7r1QVUCvm+wEhm5Ri1zhOAfxcLfglh4KLlLcNS7Ul+dX4GsRGMJKMuQfOpLEixR gwU3C/dECGBpe0rLgADp2TyoAXRq6gM/6EYE30LI9Llwg9z18xiFP3PNvAUMGLiTYC 9kTnCYrYqc79N0QRx7pf5oOhOXRh/o6brZJRhtwY= From: Eric Biggers To: linux-ext4@vger.kernel.org Cc: Daniel Rosenberg , stable@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, Al Viro , linux-fsdevel@vger.kernel.org, Gabriel Krisman Bertazi Subject: [PATCH v2] ext4: avoid utf8_strncasecmp() with unstable name Date: Mon, 1 Jun 2020 13:05:43 -0700 Message-Id: <20200601200543.59417-1-ebiggers@kernel.org> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Eric Biggers If the dentry name passed to ->d_compare() fits in dentry::d_iname, then it may be concurrently modified by a rename. This can cause undefined behavior (possibly out-of-bounds memory accesses or crashes) in utf8_strncasecmp(), since fs/unicode/ isn't written to handle strings that may be concurrently modified. Fix this by first copying the filename to a stack buffer if needed. This way we get a stable snapshot of the filename. Fixes: b886ee3e778e ("ext4: Support case-insensitive file name lookups") Cc: # v5.2+ Cc: Al Viro Cc: Daniel Rosenberg Cc: Gabriel Krisman Bertazi Signed-off-by: Eric Biggers --- v2: use memcpy() + barrier() instead of a byte-by-byte copy. fs/ext4/dir.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c index c654205f648dd..1d82336b1cd45 100644 --- a/fs/ext4/dir.c +++ b/fs/ext4/dir.c @@ -675,6 +675,7 @@ static int ext4_d_compare(const struct dentry *dentry, unsigned int len, struct qstr qstr = {.name = str, .len = len }; const struct dentry *parent = READ_ONCE(dentry->d_parent); const struct inode *inode = READ_ONCE(parent->d_inode); + char strbuf[DNAME_INLINE_LEN]; if (!inode || !IS_CASEFOLDED(inode) || !EXT4_SB(inode->i_sb)->s_encoding) { @@ -683,6 +684,21 @@ static int ext4_d_compare(const struct dentry *dentry, unsigned int len, return memcmp(str, name->name, len); } + /* + * If the dentry name is stored in-line, then it may be concurrently + * modified by a rename. If this happens, the VFS will eventually retry + * the lookup, so it doesn't matter what ->d_compare() returns. + * However, it's unsafe to call utf8_strncasecmp() with an unstable + * string. Therefore, we have to copy the name into a temporary buffer. + */ + if (len <= DNAME_INLINE_LEN - 1) { + memcpy(strbuf, str, len); + strbuf[len] = 0; + qstr.name = strbuf; + /* prevent compiler from optimizing out the temporary buffer */ + barrier(); + } + return ext4_ci_compare(inode, name, &qstr, false); } -- 2.26.2