Re: [PATCH v6 4/6] linux ttyname and ttyname_r: Make the TTY equivalence checks consistent

[Christian Brauner <christian dot brauner at mailbox dot org>]

On Fri, Nov 10, 2017 at 03:08:25PM -0500, Luke Shumaker wrote:
> From: Luke Shumaker <lukeshu@parabola.nu>
> 
> In the ttyname and ttyname_r routines on Linux, at several points it needs
> to check if a given TTY is the TTY we are looking for.  It used to be that
> this check 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, one of the changes made in commit
> 15e9a4f378c8607c2ae1aa465436af4321db0e23 was to change that check 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, it made the st_ino and st_dev parts of the check happen even if we
> have the st_rdev member.  This is an important change, because the kernel
> allows multiple devpts filesystem instances to be created; a device file in
> one devpts instance may share the same st_rdev with a file in another
> devpts instance, but they aren't the same file.
> 
> This check appears twice in each file (ttyname.c and ttyname_r.c), once (in
> ttyname and __ttyname_r) to check if a candidate file found by inspecting
> /proc is the desired TTY, and once (in getttyname and getttyname_r) to
> check if a candidate file found by searching /dev is the desired TTY.
> However, 15e9a4f only updated the checks for files found via /proc; but the
> concern about collisions between devpts instances is just as valid for
> files found via /dev.
> 
> So, update all 4 occurrences the check to be consistent with the version of
> the check introduced in 15e9a4f.  Make it easy to keep all 4 occurrences of
> the check consistent by pulling it in to a static inline function,
> is_mytty.
> 
> v2:
>  - Rearrange commit order
>  - Expand commit message
>  - Reformat is_mytty
>  - Have is_pty and is_mytty return bool instead of int
>  - Specify 'const' on pointer arguments as necessary
> v3:
>  - Revise commit message
>  - Revise ChangeLog message
>  - Split is_pty change into a separate commit
>  - Fix whitespace style
> ---
>  ChangeLog                           |  7 +++++++
>  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, 36 insertions(+), 64 deletions(-)

Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>

> 
> diff --git a/ChangeLog b/ChangeLog
> index 11709a01ac..f28c7c1afc 100644
> --- a/ChangeLog
> +++ b/ChangeLog
> @@ -1,5 +1,12 @@
>  2017-11-07  Luke Shumaker  <lukeshu@parabola.nu>
>  
> +	[BZ #22145]
> +	* sysdeps/unix/sysv/linux/ttyname.h (is_mytty): New function.
> +	* sysdeps/unix/sysv/linux/ttyname.c (getttyname): Call is_mytty.
> +	(ttyname): Likewise.
> +	* sysdeps/unix/sysv/linux/ttyname_r.c (getttyname_r): Likewise.
> +	(__ttyname_r): Likewise.
> +
>  	* sysdeps/unix/sysv/linux/ttyname.h (is_pty): Change return type from
>  	int to bool.
>  
> diff --git a/sysdeps/unix/sysv/linux/ttyname.c b/sysdeps/unix/sysv/linux/ttyname.c
> index 116cf350e5..6e97d2d455 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, const 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, const 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 ce4845a587..c290bfab36 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 bool
> +is_mytty (const struct stat64 *mytty, const struct stat64 *maybe)
> +{
> +  return (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
> +	  );
> +}
> diff --git a/sysdeps/unix/sysv/linux/ttyname_r.c b/sysdeps/unix/sysv/linux/ttyname_r.c
> index 18f35ef2b7..58eb919c3f 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,
> +			 const 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, const 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;
> -- 
> 2.15.0
>

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