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bh=9iuQw4oBOJmmh92bEqn9/c7IbdmVFU2VnRDwXJhZ5bY=; b=T duJ16xE+Hm7/r7TeN32czhWV9J5lqCyNrF0M3u7CerKGjPLzAxNAc5P44a/8fsu6AZbh/ykwtZVn9 wuoK3fsNJKmXaR5/whdH4UjsX4aQur49p5c/RWJA5pL2jinTAG8o1Cpdz1ZS1cSFp4swHBwPQt2Iy bcQU1gXq+9M93phI=; Received: from mail.kernel.org ([198.145.29.99]) by sfi-mx-1.v28.lw.sourceforge.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.92.2) id 1jfqij-000j3Y-2s for linux-f2fs-devel@lists.sourceforge.net; Mon, 01 Jun 2020 20:07:42 +0000 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 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 X-Headers-End: 1jfqij-000j3Y-2s Subject: [f2fs-dev] [PATCH v2] ext4: avoid utf8_strncasecmp() with unstable name X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Daniel Rosenberg , stable@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, Al Viro , linux-fsdevel@vger.kernel.org, Gabriel Krisman Bertazi Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net 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 _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel