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Re: [PATCH 4/5] linux ttyname and ttyname_r: Make the TTY equivalence tests consistent [BZ #22145]
- From: Christian Brauner <christian dot brauner at mailbox dot org>
- To: Luke Shumaker <lukeshu at parabola dot nu>
- Cc: libc-alpha at sourceware dot org, christian dot brauner at ubuntu dot com
- Date: Thu, 12 Oct 2017 13:16:15 +0200 (CEST)
- Subject: Re: [PATCH 4/5] linux ttyname and ttyname_r: Make the TTY equivalence tests consistent [BZ #22145]
- Authentication-results: sourceware.org; auth=none
- References: <20171012035321.22094-1-lukeshu@parabola.nu> <20171012035321.22094-5-lukeshu@parabola.nu>
On Wed, Oct 11, 2017 at 11:53:20PM -0400, Luke Shumaker wrote:
> In the ttyname and ttyname_r routines on Linux, at several points it
> it needs to test if a given TTY is the TTY we are looking for. It used to
> be that this test was (to see if `maybe` is `mytty`):
>
> __xstat64(_STAT_VER, maybe_filename, &maybe) == 0
> #ifdef _STATBUF_ST_RDEV
> && S_ISCHR(maybe.st_mode) && maybe.st_rdev == mytty.st_rdev
> #else
> && maybe.st_ino == mytty.st_ino && maybe.st_dev == mytty.st_dev
> #endif
>
> This check appears in several places.
>
> Then, in commit 15e9a4f3 by Christian Brauner
> <christian.brauner@canonical.com>, that check changed to:
>
> __xstat64(_STAT_VER, maybe_filename, &maybe) == 0
> #ifdef _STATBUF_ST_RDEV
> && S_ISCHR(maybe.st_mode) && maybe.st_rdev == mytty.st_rdev
> #endif
> && maybe.st_ino == mytty.st_ino && maybe.st_dev == mytty.st_dev
>
> That is, he made st_ino and st_dev checks happen even if we have the
> st_rdev member. This is a good change, because kernel namespaces allow you
> to create a new namespace, and to create a new device with the same
> st_rdev, but isn't the same file.
>
> However, this check appears twice in each file (ttyname.c and
> ttyname_r.c), but Christian only changed it in one place in each file.
> Now, that kind-of made sense. The common use-case for this is that
> you're in a chroot, and have inherited a file descriptor to a TTY
> outside of the chroot. In the ttyname routine, the first check is on
> the passed-in file descriptor, while the remaining checks are for
> files we open by their absolute path; so we'd expect them to be in the
> new namespace. But that's just the "normal" situation, users can do
> all kinds of funny things, so update the check everywhere.
>
> Make it easy to keep consistent by pulling the check in to a static inline
> function.
> ---
> ChangeLog | 5 +++++
> sysdeps/unix/sysv/linux/ttyname.c | 40 ++++++++----------------------------
> sysdeps/unix/sysv/linux/ttyname.h | 12 +++++++++++
> sysdeps/unix/sysv/linux/ttyname_r.c | 41 ++++++++-----------------------------
> 4 files changed, 34 insertions(+), 64 deletions(-)
>
> diff --git a/ChangeLog b/ChangeLog
> index 1921f8883b..5973b9d50b 100644
> --- a/ChangeLog
> +++ b/ChangeLog
> @@ -1,5 +1,10 @@
> 2017-10-11 Luke Shumaker <lukeshu@parabola.nu>
>
> + [BZ #22145]
> + * sysdeps/unix/sysv/linux/ttyname.h (is_mytty): New function.
> + * sysdeps/unix/sysv/linux/ttyname.c: Call it.
> + * sysdeps/unix/sysv/linux/ttyname_r.c: Likewise.
> +
> [BZ #22145]
> * sysdeps/unix/sysv/linux/tst-ttyname.c: New file.
> * sysdeps/unix/sysv/linux/Makefile: Add tst-ttyname to tests.
> diff --git a/sysdeps/unix/sysv/linux/ttyname.c b/sysdeps/unix/sysv/linux/ttyname.c
> index 116cf350e5..138a8a57f8 100644
> --- a/sysdeps/unix/sysv/linux/ttyname.c
> +++ b/sysdeps/unix/sysv/linux/ttyname.c
> @@ -35,14 +35,14 @@
> char *__ttyname;
> #endif
>
> -static char *getttyname (const char *dev, dev_t mydev,
> - ino64_t myino, int save, int *dostat);
> +static char *getttyname (const char *dev, struct stat64 *mytty,
> + int save, int *dostat);
>
> libc_freeres_ptr (static char *getttyname_name);
>
> static char *
> attribute_compat_text_section
> -getttyname (const char *dev, dev_t mydev, ino64_t myino, int save, int *dostat)
> +getttyname (const char *dev, struct stat64 *mytty, int save, int *dostat)
> {
> static size_t namelen;
> struct stat64 st;
> @@ -63,7 +63,7 @@ getttyname (const char *dev, dev_t mydev, ino64_t myino, int save, int *dostat)
> *((char *) __mempcpy (getttyname_name, dev, devlen - 1)) = '/';
>
> while ((d = __readdir64 (dirstream)) != NULL)
> - if ((d->d_fileno == myino || *dostat)
> + if ((d->d_fileno == mytty->st_ino || *dostat)
> && strcmp (d->d_name, "stdin")
> && strcmp (d->d_name, "stdout")
> && strcmp (d->d_name, "stderr"))
> @@ -85,12 +85,7 @@ getttyname (const char *dev, dev_t mydev, ino64_t myino, int save, int *dostat)
> }
> memcpy (&getttyname_name[devlen], d->d_name, dlen);
> if (__xstat64 (_STAT_VER, getttyname_name, &st) == 0
> -#ifdef _STATBUF_ST_RDEV
> - && S_ISCHR (st.st_mode) && st.st_rdev == mydev
> -#else
> - && d->d_fileno == myino && st.st_dev == mydev
> -#endif
> - )
> + && is_mytty (mytty, &st))
> {
> (void) __closedir (dirstream);
> #if 0
> @@ -167,12 +162,7 @@ ttyname (int fd)
> /* Verify readlink result, fall back on iterating through devices. */
> if (ttyname_buf[0] == '/'
> && __xstat64 (_STAT_VER, ttyname_buf, &st1) == 0
> -#ifdef _STATBUF_ST_RDEV
> - && S_ISCHR (st1.st_mode)
> - && st1.st_rdev == st.st_rdev
> -#endif
> - && st1.st_ino == st.st_ino
> - && st1.st_dev == st.st_dev)
> + && is_mytty (&st, &st1))
> return ttyname_buf;
>
> /* If the link doesn't exist, then it points to a device in another
> @@ -186,11 +176,7 @@ ttyname (int fd)
>
> if (__xstat64 (_STAT_VER, "/dev/pts", &st1) == 0 && S_ISDIR (st1.st_mode))
> {
> -#ifdef _STATBUF_ST_RDEV
> - name = getttyname ("/dev/pts", st.st_rdev, st.st_ino, save, &dostat);
> -#else
> - name = getttyname ("/dev/pts", st.st_dev, st.st_ino, save, &dostat);
> -#endif
> + name = getttyname ("/dev/pts", &st, save, &dostat);
> }
> else
> {
> @@ -200,21 +186,13 @@ ttyname (int fd)
>
> if (!name && dostat != -1)
> {
> -#ifdef _STATBUF_ST_RDEV
> - name = getttyname ("/dev", st.st_rdev, st.st_ino, save, &dostat);
> -#else
> - name = getttyname ("/dev", st.st_dev, st.st_ino, save, &dostat);
> -#endif
> + name = getttyname ("/dev", &st, save, &dostat);
> }
>
> if (!name && dostat != -1)
> {
> dostat = 1;
> -#ifdef _STATBUF_ST_RDEV
> - name = getttyname ("/dev", st.st_rdev, st.st_ino, save, &dostat);
> -#else
> - name = getttyname ("/dev", st.st_dev, st.st_ino, save, &dostat);
> -#endif
> + name = getttyname ("/dev", &st, save, &dostat);
> }
>
> return name;
> diff --git a/sysdeps/unix/sysv/linux/ttyname.h b/sysdeps/unix/sysv/linux/ttyname.h
> index dd7873d1ff..15f7b066b6 100644
> --- a/sysdeps/unix/sysv/linux/ttyname.h
> +++ b/sysdeps/unix/sysv/linux/ttyname.h
> @@ -33,3 +33,15 @@ is_pty (struct stat64 *sb)
> return false;
> #endif
> }
> +
> +static inline int
> +is_mytty(struct stat64 *mytty, struct stat64 *maybe)
> +{
> + return 1
> +#ifdef _STATBUF_ST_RDEV
> + && S_ISCHR (maybe->st_mode)
> + && maybe->st_rdev == mytty->st_rdev
> +#endif
> + && maybe->st_ino == mytty->st_ino
> + && maybe->st_dev == mytty->st_dev;
> +}
I find that hard to read. At first I thought this would unconditionally return
1. I'd rather prefer something like (In the appropriate GNU coding style
eventually of course.):
static inline bool is_mytty(struct stat64 *mytty, struct stat64 *maybe)
{
if (maybe->st_ino == mytty->st_ino && maybe->st_dev == mytty->st_dev
#ifdef _STATBUF_ST_RDEV
&& S_ISCHR(maybe->st_mode) && maybe->st_rdev == mytty->st_rdev
#endif
)
return true;
return false;
}
But others might be fine with it. But I think having it return a bool here is
perfectly fine since there's no other possible outcome than true or false.
diff --git a/sysdeps/unix/sysv/linux/ttyname_r.c b/sysdeps/unix/sysv/linux/ttyname_r.c
index 18f35ef2b7..d975d95d0d 100644
--- a/sysdeps/unix/sysv/linux/ttyname_r.c
+++ b/sysdeps/unix/sysv/linux/ttyname_r.c
@@ -31,12 +31,12 @@
#include "ttyname.h"
static int getttyname_r (char *buf, size_t buflen,
- dev_t mydev, ino64_t myino, int save,
+ struct stat64 *mytty, int save,
int *dostat);
static int
attribute_compat_text_section
-getttyname_r (char *buf, size_t buflen, dev_t mydev, ino64_t myino,
+getttyname_r (char *buf, size_t buflen, struct stat64 *mytty,
int save, int *dostat)
{
struct stat64 st;
@@ -52,7 +52,7 @@ getttyname_r (char *buf, size_t buflen, dev_t mydev, ino64_t myino,
}
while ((d = __readdir64 (dirstream)) != NULL)
- if ((d->d_fileno == myino || *dostat)
+ if ((d->d_fileno == mytty->st_ino || *dostat)
&& strcmp (d->d_name, "stdin")
&& strcmp (d->d_name, "stdout")
&& strcmp (d->d_name, "stderr"))
@@ -72,12 +72,7 @@ getttyname_r (char *buf, size_t buflen, dev_t mydev, ino64_t myino,
cp[0] = '\0';
if (__xstat64 (_STAT_VER, buf, &st) == 0
-#ifdef _STATBUF_ST_RDEV
- && S_ISCHR (st.st_mode) && st.st_rdev == mydev
-#else
- && d->d_fileno == myino && st.st_dev == mydev
-#endif
- )
+ && is_mytty (mytty, &st))
{
(void) __closedir (dirstream);
__set_errno (save);
@@ -151,12 +146,7 @@ __ttyname_r (int fd, char *buf, size_t buflen)
/* Verify readlink result, fall back on iterating through devices. */
if (buf[0] == '/'
&& __xstat64 (_STAT_VER, buf, &st1) == 0
-#ifdef _STATBUF_ST_RDEV
- && S_ISCHR (st1.st_mode)
- && st1.st_rdev == st.st_rdev
-#endif
- && st1.st_ino == st.st_ino
- && st1.st_dev == st.st_dev)
+ && is_mytty (&st, &st1))
return 0;
/* If the link doesn't exist, then it points to a device in another
@@ -175,13 +165,8 @@ __ttyname_r (int fd, char *buf, size_t buflen)
if (__xstat64 (_STAT_VER, buf, &st1) == 0 && S_ISDIR (st1.st_mode))
{
-#ifdef _STATBUF_ST_RDEV
- ret = getttyname_r (buf, buflen, st.st_rdev, st.st_ino, save,
+ ret = getttyname_r (buf, buflen, &st, save,
&dostat);
-#else
- ret = getttyname_r (buf, buflen, st.st_dev, st.st_ino, save,
- &dostat);
-#endif
}
else
{
@@ -193,26 +178,16 @@ __ttyname_r (int fd, char *buf, size_t buflen)
{
buf[sizeof ("/dev/") - 1] = '\0';
buflen += sizeof ("pts/") - 1;
-#ifdef _STATBUF_ST_RDEV
- ret = getttyname_r (buf, buflen, st.st_rdev, st.st_ino, save,
- &dostat);
-#else
- ret = getttyname_r (buf, buflen, st.st_dev, st.st_ino, save,
+ ret = getttyname_r (buf, buflen, &st, save,
&dostat);
-#endif
}
if (ret && dostat != -1)
{
buf[sizeof ("/dev/") - 1] = '\0';
dostat = 1;
-#ifdef _STATBUF_ST_RDEV
- ret = getttyname_r (buf, buflen, st.st_rdev, st.st_ino,
- save, &dostat);
-#else
- ret = getttyname_r (buf, buflen, st.st_dev, st.st_ino,
+ ret = getttyname_r (buf, buflen, &st,
save, &dostat);
-#endif
}
return ret;
--
2.14.2