From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL autolearn=ham autolearn_force=no version=3.4.2 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by inbox.vuxu.org (OpenSMTPD) with SMTP id 867a6512 for ; Wed, 19 Feb 2020 14:16:51 +0000 (UTC) Received: (qmail 28470 invoked by uid 550); 19 Feb 2020 14:16:49 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 28446 invoked from network); 19 Feb 2020 14:16:48 -0000 Date: Wed, 19 Feb 2020 09:16:36 -0500 From: Rich Felker To: musl@lists.openwall.com Message-ID: <20200219141636.GG1663@brightrain.aerifal.cx> References: <2dd69ee3939f469ab98a07d5337a8bf0@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2dd69ee3939f469ab98a07d5337a8bf0@huawei.com> User-Agent: Mutt/1.5.21 (2010-09-15) Subject: Re: [musl] [PATCH] stdio: Fix fdopen bug On Wed, Feb 19, 2020 at 06:47:53AM +0000, zhangtianci wrote: > > On Wed, Feb 19, 2020 at 10:37:29AM +0800, Zhang Tianci wrote: > > > Currently, in musl the fdopen doesn't check the consistence between > > > fd's mode and corresponding file's mode. > > > > > > For example, > > > > > > int fd = open("file1", O_RDONLY); > > > FILE *f = fdopen(fd, "W") > > > > > > In musl, above code will be Okay. > > > While according to POSIX, above code (fdopen) will return EINVAL. > > > > > > Signed-off-by: Zhang Tianci > > > --- > > > src/stdio/__fdopen.c | 10 ++++++++++ > > > 1 file changed, 10 insertions(+) > > > > > > diff --git a/src/stdio/__fdopen.c b/src/stdio/__fdopen.c index > > > 116e78e..23c4ffd 100644 > > > --- a/src/stdio/__fdopen.c > > > +++ b/src/stdio/__fdopen.c > > > @@ -26,6 +26,16 @@ FILE *__fdopen(int fd, const char *mode) > > > /* Impose mode restrictions */ > > > if (!strchr(mode, '+')) f->flags = (*mode == 'r') ? F_NOWR : F_NORD; > > > > > > + int fd_flag = __syscall(SYS_fcntl, fd, F_GETFL); > > > + > > > + if (fd_flag == -1) return 0; > > > + > > > + if (((fd_flag & O_ACCMODE) == O_RDONLY && !(f->flags & F_NORD)) > > || > > > + ((fd_flag & O_ACCMODE) == O_WRONLY && !(f->flags & > > F_NOWR))) { > > > + errno = EINVAL; > > > + return 0; > > > + } > > > + > > > /* Apply close-on-exec flag */ > > > if (strchr(mode, 'e')) __syscall(SYS_fcntl, fd, F_SETFD, > > > FD_CLOEXEC); > > > > > > -- > > > 2.17.1 > > > > Per POSIX this is a "may fail" not a "shall fail". Testing for this is more costly > > (see added code/syscalls in the patch) and serves no purpose, which is why > > it's not done. > > > > Rich > > POSIX's require on fdopen: > > The application shall ensure that the mode of the stream as expressed by the ^^^^^^^^^^^^^^^ > mode argument is allowed by the file access mode of the open file description > to which fildes refers. > > So I think the example above should return EINVAL. The text you're quoting is placing a requirement on the application, not the implementation. If the application fails to meet a "shall", it has undefined behavior and there are no obligations whatsoever on the implementation. The error is clearly a "may fail" if you read the ERRORS section of the specification. Rich