From patchwork Fri Apr 15 18:47:46 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Serge Hallyn X-Patchwork-Id: 11765 Received: (qmail 30905 invoked by alias); 15 Apr 2016 18:48:04 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 30863 invoked by uid 89); 15 Apr 2016 18:48:02 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=0.5 required=5.0 tests=AWL, BAYES_50, KAM_LAZY_DOMAIN_SECURITY autolearn=no version=3.3.2 spammy=UD:st.st_rdev, stst_rdev, UD:st_rdev, st1st_dev X-HELO: youngberry.canonical.com Date: Fri, 15 Apr 2016 18:47:46 +0000 From: Serge Hallyn To: Florian Weimer , libc-alpha@sourceware.org Cc: Serge Hallyn Subject: Re: [PATCH 1/1] linux ttyname: return link if appropriate Message-ID: <20160415184746.GA10830@ubuntumail> References: <20160415152929.GA7932@ubuntumail> <5711165D.5040902@redhat.com> <20160415164652.GE8450@ubuntumail> <57111F9C.8030902@redhat.com> <20160415174245.GA9610@ubuntumail> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20160415174245.GA9610@ubuntumail> User-Agent: Mutt/1.5.21 (2010-09-15) Quoting Serge Hallyn (serge.hallyn@ubuntu.com): > Quoting Florian Weimer (fweimer@redhat.com): > > On 04/15/2016 06:46 PM, Serge Hallyn wrote: > > >Quoting Florian Weimer (fweimer@redhat.com): > > >>On 04/15/2016 05:29 PM, Serge Hallyn wrote: > > >>>The current ttyname does the wrong thing in two cases: > > >>> > > >>>1. If the passed-in link (say /proc/self/fd/0) points to a > > >>>device, say /dev/pts/2, in a parent mount namespace, and a > > >>>/dev/pts/2 exists (in a different devpts) in the current > > >>>namespace, then it returns /dev/pts/2. But /dev/pts/2 is > > >>>NOT the current tty, it is a different file and device. > > >> > > >>Is this the first change? > > > > > >Right, it ensures that the filesystem of the two files is > > >the same. > > > > > >>>2. If the passed-in link (say /proc/self/fd/0) points to > > >>>a device, say /dev/pts/2, in a parent mount namespace, and > > >>>/dev/pts/2 does not exist in the current namespace, it > > >>>returns success but an empty name. As far as I can tell, > > >>>there is no reason for it to not return /proc/self/fd/0. > > >>>http://pubs.opengroup.org/onlinepubs/009695399/functions/ttyname.html > > >>>does not say anything about not returning a link. > > >> > > >>Is it safe to drop the verification that ttyname ordinarily would do? > > > > > >Which verification do you mean exactly? > > > > That the file descriptor actually belongs to a PTY device listed > > under /dev/pts. > > Oh, yeah. I think that adding a chck that this is a pts (using st_rdev) > before returning "/proc/self/fd/N" (in my newly added block) would be good. Something like: From ba0dc51e90d884b107145924821a1e8caf43a468 Mon Sep 17 00:00:00 2001 From: Serge Hallyn Date: Fri, 15 Apr 2016 10:21:07 -0500 Subject: [PATCH 1/1] linux ttyname: return link if appropriate The current ttyname does the wrong thing in two cases: 1. If the passed-in link (say /proc/self/fd/0) points to a device, say /dev/pts/2, in a parent mount namespace, and a /dev/pts/2 exists (in a different devpts) in the current namespace, then it returns /dev/pts/2. But /dev/pts/2 is NOT the current tty, it is a different file and device. 2. If the passed-in link (say /proc/self/fd/0) points to a device, say /dev/pts/2, in a parent mount namespace, and /dev/pts/2 does not exist in the current namespace, it returns success but an empty name. As far as I can tell, there is no reason for it to not return /proc/self/fd/0. http://pubs.opengroup.org/onlinepubs/009695399/functions/ttyname.html does not say anything about not returning a link. Signed-off-by: Serge Hallyn --- sysdeps/unix/sysv/linux/ttyname.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/sysdeps/unix/sysv/linux/ttyname.c b/sysdeps/unix/sysv/linux/ttyname.c index 7a001b4..54d0e6b 100644 --- a/sysdeps/unix/sysv/linux/ttyname.c +++ b/sysdeps/unix/sysv/linux/ttyname.c @@ -33,6 +33,21 @@ char *__ttyname; #endif +/* + * Return true if this is a UNIX98 pty device, as defined in + * linux/Documentation/devices.txt + */ +static int +is_pty (struct stat *sb) +{ +#ifdef _STATBUF_ST_RDEV + int m = major (sb.st_rdev); + return (136 <= m && m <= 143); +#else + return false; +#endif +} + static char *getttyname (const char *dev, dev_t mydev, ino64_t myino, int save, int *dostat) internal_function; @@ -170,12 +185,22 @@ ttyname (int fd) #ifdef _STATBUF_ST_RDEV && S_ISCHR (st1.st_mode) && st1.st_rdev == st.st_rdev + && st1.st_dev == st.st_dev #else && st1.st_ino == st.st_ino && st1.st_dev == st.st_dev #endif ) return ttyname_buf; + /* If the link doesn't exist, then it points to a dvice in another + * namespace. If it is a UNIX98 pty, then return the /proc/self + * fd, as it points to a name unreachable in our namespace */ + if (is_pty (st) && strlen (procname) < buflen - 1) + { + memcpy (ttyname_buf, procname, strlen (procname)); + ttyname_buf[strlen (procname)] = '\0'; + return ttyname_buf; + } } if (__xstat64 (_STAT_VER, "/dev/pts", &st1) == 0 && S_ISDIR (st1.st_mode))