Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933624AbbFJH7r (ORCPT ); Wed, 10 Jun 2015 03:59:47 -0400 Received: from linuxhacker.ru ([217.76.32.60]:43115 "EHLO fiona.linuxhacker.ru" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S933555AbbFJH7b convert rfc822-to-8bit (ORCPT ); Wed, 10 Jun 2015 03:59:31 -0400 Subject: Re: [PATCH 2/2] staging/lustre/llite: fix ll_getname user buffer copy Mime-Version: 1.0 (Apple Message framework v1283) Content-Type: text/plain; charset=windows-1252 From: Oleg Drokin In-Reply-To: <20150610075209.GC28762@mwanda> Date: Wed, 10 Jun 2015 03:59:16 -0400 Cc: Greg Kroah-Hartman , devel@driverdev.osuosl.org, Andreas Dilger , Linux Kernel Mailing List Content-Transfer-Encoding: 8BIT Message-Id: <52AED89D-753F-4A91-824F-53410267F2FD@linuxhacker.ru> References: <1433911283-24902-1-git-send-email-green@linuxhacker.ru> <1433911283-24902-3-git-send-email-green@linuxhacker.ru> <20150610075209.GC28762@mwanda> To: Dan Carpenter X-Mailer: Apple Mail (2.1283) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2970 Lines: 79 On Jun 10, 2015, at 3:52 AM, Dan Carpenter wrote: > On Wed, Jun 10, 2015 at 12:41:23AM -0400, green@linuxhacker.ru wrote: >> From: Oleg Drokin >> >> strncpy_from_user could return negative values on error, >> so need to take those into account. >> Since ll_getname is used to get a single component name from userspace >> to transfer to server as-is, there's no need to allocate 4k buffer >> as done by __getname. Allocate NAME_MAX+1 buffer instead to ensure >> we have enough for a null terminated max valid length buffer. >> >> This was discovered by Al Viro in https://lkml.org/lkml/2015/4/11/243 >> >> Signed-off-by: Oleg Drokin >> --- >> drivers/staging/lustre/lustre/llite/dir.c | 20 +++++++++++--------- >> 1 file changed, 11 insertions(+), 9 deletions(-) >> >> diff --git a/drivers/staging/lustre/lustre/llite/dir.c b/drivers/staging/lustre/lustre/llite/dir.c >> index 87a042c..e0b9043 100644 >> --- a/drivers/staging/lustre/lustre/llite/dir.c >> +++ b/drivers/staging/lustre/lustre/llite/dir.c >> @@ -1213,29 +1213,31 @@ out: >> return rc; >> } >> >> -static char * >> -ll_getname(const char __user *filename) >> +/* This function tries to get a single name component, >> + * to send to the server. No actual path traversal involved, >> + * so we limit to NAME_MAX */ >> +static char *ll_getname(const char __user *filename) >> { >> int ret = 0, len; >> - char *tmp = __getname(); >> + char *tmp = kzalloc(NAME_MAX + 1, GFP_KERNEL); > > Doing allocations in the declaration block is rare in the kernel but it > accounts for around a quarter of the missing NULL checks and many memory > leaks in the kbuild zero day bot testing. It's a bad idea and some > subsystems ban the practice, but Greg is fine with it so I'm not going > to complain. Fair. I can redo this. >> >> if (!tmp) >> return ERR_PTR(-ENOMEM); >> >> - len = strncpy_from_user(tmp, filename, PATH_MAX); >> - if (len == 0) >> + len = strncpy_from_user(tmp, filename, NAME_MAX); >> + if (len < 0) >> + ret = len; >> + else if (len == 0) >> ret = -ENOENT; >> - else if (len > PATH_MAX) >> - ret = -ENAMETOOLONG; > > I don't like how this does silent truncation. strncpy_from_user() > return -EFAULT if we run into unmapped memory. Otherwise if the user > supplies a too long name it returns len == PATH_MAX. (I think, the > documentation for this function is hard to understand). > > Of course, the check was never true in the original code? Right. It's no big deal to ask for NAME_MAX+1 and then restore the len > NAME_MAX check and return -ENAMETOOLONG in that case. Then the silent truncate is gone and logic wise we don't care all that much either way, I imagine. Bye, Oleg-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/