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linux ttyname{_r}: Make tty checks consistent

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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 15e9a4f378
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.

Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
This commit is contained in:
Luke Shumaker
2017-11-15 20:34:30 +01:00
committed by Christian Brauner
parent d10d6cab16
commit 2fbce9c203
4 changed files with 36 additions and 64 deletions
Download Patch File Download Diff File Expand all files Collapse all files

40
sysdeps/unix/sysv/linux/ttyname.c
View File

@ -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;