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[PATCH 5/5] linux ttyname and ttyname_r: Fix namespace check [BZ #22145]
- From: Luke Shumaker <lukeshu at parabola dot nu>
- To: libc-alpha at sourceware dot org
- Cc: christian dot brauner at mailbox dot org
- Date: Wed, 11 Oct 2017 23:53:21 -0400
- Subject: [PATCH 5/5] linux ttyname and ttyname_r: Fix namespace check [BZ #22145]
- Authentication-results: sourceware.org; auth=none
- References: <20171012035321.22094-1-lukeshu@parabola.nu>
In commit 15e9a4f Christian Brauner introduced logic for ttyname() sending
back ENODEV to signal that we can't get a name for the TTY because we
inherited it from a different mount namespace.
However, just because we inherited it from a different mount namespace, and
it isn't available at its original path, doesn't mean that its name is
unknowable; we can still find it by allowing the normal fall back on
iterating through devices.
A common scenario where this happens is with "/dev/console" in
containers. Common container managers (including systemd-nspawn) will
call openpty() on a ptmx device in the host's mount namespace to
allocate a pty master/slave pair, then send the slave FD to the
container, and bind-mounted at "/dev/console" in the container's mount
namespace. Inside of the container, the slave-end isn't available at
its original path ("/dev/pts/$X"), since the container mount namespace
has a separate devpts instance from the host (that path may or may not
exist in the container; if it does exist, it's not the same PTY slave
device). Currently ttyname{_r}() sees that the original path isn't a
match, and fails early and gives up, even though if it kept searching
it would find the TTY at "/dev/console". This fixes that so that the
ENODEV path does not force an early return inhibiting the fall-back
search.
---
ChangeLog | 5 +++++
sysdeps/unix/sysv/linux/ttyname.c | 19 ++++++++++++-------
sysdeps/unix/sysv/linux/ttyname_r.c | 20 ++++++++++++--------
3 files changed, 29 insertions(+), 15 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 5973b9d50b..28f31d345b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
2017-10-11 Luke Shumaker <lukeshu@parabola.nu>
+ [BZ #22145]
+ * sysdeps/unix/sysv/linux/ttyname.c (ttyname):
+ Defer is_pty check until end.
+ * sysdeps/unix/sysv/linux/ttyname_r.c (ttyname_r): Likewise.
+
[BZ #22145]
* sysdeps/unix/sysv/linux/ttyname.h (is_mytty): New function.
* sysdeps/unix/sysv/linux/ttyname.c: Call it.
diff --git a/sysdeps/unix/sysv/linux/ttyname.c b/sysdeps/unix/sysv/linux/ttyname.c
index 138a8a57f8..ebd916f68e 100644
--- a/sysdeps/unix/sysv/linux/ttyname.c
+++ b/sysdeps/unix/sysv/linux/ttyname.c
@@ -115,6 +115,7 @@ ttyname (int fd)
char procname[30];
struct stat64 st, st1;
int dostat = 0;
+ int doispty = 0;
char *name;
int save = errno;
struct termios term;
@@ -165,13 +166,7 @@ ttyname (int fd)
&& is_mytty (&st, &st1))
return ttyname_buf;
- /* If the link doesn't exist, then it points to a device in another
- namespace. */
- if (is_pty (&st))
- {
- __set_errno (ENODEV);
- return NULL;
- }
+ doispty = 1;
}
if (__xstat64 (_STAT_VER, "/dev/pts", &st1) == 0 && S_ISDIR (st1.st_mode))
@@ -195,5 +190,15 @@ ttyname (int fd)
name = getttyname ("/dev", &st, save, &dostat);
}
+ if (!name && doispty && is_pty (&st))
+ {
+ /* We failed to figure out the TTY's name, but we can at least
+ * signal that we did verify that it really is a PTY slave.
+ * This happens when we have inherited the file descriptor from
+ * a different mount namespace. */
+ __set_errno (ENODEV);
+ return NULL;
+ }
+
return name;
}
diff --git a/sysdeps/unix/sysv/linux/ttyname_r.c b/sysdeps/unix/sysv/linux/ttyname_r.c
index d975d95d0d..adcffacb2c 100644
--- a/sysdeps/unix/sysv/linux/ttyname_r.c
+++ b/sysdeps/unix/sysv/linux/ttyname_r.c
@@ -95,6 +95,7 @@ __ttyname_r (int fd, char *buf, size_t buflen)
char procname[30];
struct stat64 st, st1;
int dostat = 0;
+ int doispty = 0;
int save = errno;
/* Test for the absolute minimal size. This makes life easier inside
@@ -149,14 +150,7 @@ __ttyname_r (int fd, char *buf, size_t buflen)
&& is_mytty (&st, &st1))
return 0;
- /* If the link doesn't exist, then it points to a device in another
- * namespace.
- */
- if (is_pty (&st))
- {
- __set_errno (ENODEV);
- return ENODEV;
- }
+ doispty = 1;
}
/* Prepare the result buffer. */
@@ -190,6 +184,16 @@ __ttyname_r (int fd, char *buf, size_t buflen)
save, &dostat);
}
+ if (ret && doispty && is_pty (&st))
+ {
+ /* We failed to figure out the TTY's name, but we can at least
+ * signal that we did verify that it really is a PTY slave.
+ * This happens when we have inherited the file descriptor from
+ * a different mount namespace. */
+ __set_errno (ENODEV);
+ return ENODEV;
+ }
+
return ret;
}
--
2.14.2