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linux ttyname{_r}: Don't bail prematurely [BZ #22145]
Commit15e9a4f378
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 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/$X" path doesn't match the FD passed to it, and fails early and gives up, even though if it kept searching it would find the TTY at "/dev/console". Fix that; don't have the ENODEV path force an early return inhibiting the fall-back search. This change is based on the previous patch that adds use of is_mytty in getttyname and getttyname_r. Without that change, this effectively reverts15e9a4f
, which made us disregard the false similarity of file pointed to by "/proc/self/fd/$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. Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
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@ -1,5 +1,10 @@
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2017-11-15 Luke Shumaker <lukeshu@parabola.nu>
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[BZ #22145]
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* sysdeps/unix/sysv/linux/ttyname.c (ttyname):
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Defer is_pty check until end of the function.
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* sysdeps/unix/sysv/linux/ttyname_r.c (__ttyname_r): Likewise.
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[BZ #22145]
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* sysdeps/unix/sysv/linux/ttyname.h (is_mytty): New function.
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* sysdeps/unix/sysv/linux/ttyname.c (getttyname): Call is_mytty.
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@ -115,6 +115,7 @@ ttyname (int fd)
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char procname[30];
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struct stat64 st, st1;
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int dostat = 0;
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int doispty = 0;
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char *name;
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int save = errno;
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struct termios term;
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@ -165,13 +166,7 @@ ttyname (int fd)
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&& is_mytty (&st, &st1))
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return ttyname_buf;
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/* If the link doesn't exist, then it points to a device in another
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namespace. */
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if (is_pty (&st))
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{
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__set_errno (ENODEV);
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return NULL;
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}
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doispty = 1;
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}
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if (__xstat64 (_STAT_VER, "/dev/pts", &st1) == 0 && S_ISDIR (st1.st_mode))
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@ -195,5 +190,15 @@ ttyname (int fd)
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name = getttyname ("/dev", &st, save, &dostat);
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}
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if (!name && doispty && is_pty (&st))
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{
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/* We failed to figure out the TTY's name, but we can at least
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signal that we did verify that it really is a PTY slave.
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This happens when we have inherited the file descriptor from
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a different mount namespace. */
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__set_errno (ENODEV);
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return NULL;
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}
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return name;
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}
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@ -95,6 +95,7 @@ __ttyname_r (int fd, char *buf, size_t buflen)
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char procname[30];
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struct stat64 st, st1;
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int dostat = 0;
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int doispty = 0;
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int save = errno;
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/* Test for the absolute minimal size. This makes life easier inside
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@ -149,14 +150,7 @@ __ttyname_r (int fd, char *buf, size_t buflen)
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&& is_mytty (&st, &st1))
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return 0;
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/* If the link doesn't exist, then it points to a device in another
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* namespace.
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*/
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if (is_pty (&st))
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{
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__set_errno (ENODEV);
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return ENODEV;
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}
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doispty = 1;
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}
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/* Prepare the result buffer. */
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@ -190,6 +184,16 @@ __ttyname_r (int fd, char *buf, size_t buflen)
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save, &dostat);
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}
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if (ret && doispty && is_pty (&st))
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{
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/* We failed to figure out the TTY's name, but we can at least
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signal that we did verify that it really is a PTY slave.
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This happens when we have inherited the file descriptor from
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a different mount namespace. */
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__set_errno (ENODEV);
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return ENODEV;
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}
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return ret;
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}
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