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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

41
sysdeps/unix/sysv/linux/ttyname_r.c
View File

@ -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,
ret = getttyname_r (buf, buflen, &st, save,
&dostat);
#else
ret = getttyname_r (buf, buflen, st.st_dev, st.st_ino, 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,
ret = getttyname_r (buf, buflen, &st,
save, &dostat);
#else
ret = getttyname_r (buf, buflen, st.st_dev, st.st_ino,
save, &dostat);
#endif
}
return ret;