[v7,5/6] linux ttyname and ttyname_r: Don't bail prematurely [BZ #22145]
Commit Message
From: Luke Shumaker <lukeshu@parabola.nu>
Commit 15e9a4f378c8607c2ae1aa465436af4321db0e23 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 try to find it by allowing the normal fall back on
iterating through devices.
An example scenario where this happens is with "/dev/console" in
containers. It's a common practice among container managers (including
systemd-nspawn) to allocate a PTY master/slave pair in the host's mount
namespace (the slave having a path like "/dev/pty/$X"), bind mount the
slave to "/dev/console" in the container's mount namespace, and send the
slave FD to a process in the container. Inside of the container, the
slave-end isn't available at its original path ("/dev/pts/$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 file
at the original "/dev/pts/$X" path doesn't match the FD passed to it, and
fails early and gives up, even though if it kept searching it would find
the TTY at "/dev/console". Fix that; don't have the ENODEV path force an
early return inhibiting the fall-back search.
This change is based on the previous patch that adds use of is_mytty in
getttyname and getttyname_r. Without that change, this effectively reverts
15e9a4f, which made us disregard the false similarity of file pointed to by
"/proc/self/fd/$Y", because if it doesn't bail prematurely then that file
("/dev/pts/$X") will just come up again anyway in the fall-back search.
v2:
- Rearrange commit order
- Revise commit message
v3:
- Revise commit message
- Revise ChangeLog message
- Fix style of block comments
---
ChangeLog | 5 +++++
sysdeps/unix/sysv/linux/ttyname.c | 19 ++++++++++++-------
sysdeps/unix/sysv/linux/ttyname_r.c | 20 ++++++++++++--------
3 files changed, 29 insertions(+), 15 deletions(-)
@@ -1,5 +1,10 @@
2017-11-07 Luke Shumaker <lukeshu@parabola.nu>
+ [BZ #22145]
+ * sysdeps/unix/sysv/linux/ttyname.c (ttyname):
+ Defer is_pty check until end of the function.
+ * 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 (getttyname): Call is_mytty.
@@ -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;
}
@@ -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;
}