| Message ID | 20171110200827.32265-6-lukeshu@lukeshu.com |
|---|---|
| State | New |
| Headers | show |
| Series | Fixup linux ttyname and ttyname_r [BZ #22145] | expand |
On Fri, Nov 10, 2017 at 03:08:26PM -0500, Luke Shumaker wrote: > 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(-) Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com> > > diff --git a/ChangeLog b/ChangeLog > index f28c7c1afc..9ea727499c 100644 > --- a/ChangeLog > +++ b/ChangeLog > @@ -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. > diff --git a/sysdeps/unix/sysv/linux/ttyname.c b/sysdeps/unix/sysv/linux/ttyname.c > index 6e97d2d455..f4c955f25b 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 58eb919c3f..00eefc2c5c 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; > } > > -- > 2.15.0 >
diff --git a/ChangeLog b/ChangeLog index f28c7c1afc..9ea727499c 100644 --- a/ChangeLog +++ b/ChangeLog @@ -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. diff --git a/sysdeps/unix/sysv/linux/ttyname.c b/sysdeps/unix/sysv/linux/ttyname.c index 6e97d2d455..f4c955f25b 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 58eb919c3f..00eefc2c5c 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; }
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(-)