From 2fbce9c2031e70b6bd67876accfc34b0ec492878 Mon Sep 17 00:00:00 2001 From: Luke Shumaker Date: Wed, 15 Nov 2017 20:34:30 +0100 Subject: linux ttyname{_r}: Make tty checks consistent 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. Reviewed-by: Christian Brauner --- sysdeps/unix/sysv/linux/ttyname.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'sysdeps/unix/sysv/linux/ttyname.h') diff --git a/sysdeps/unix/sysv/linux/ttyname.h b/sysdeps/unix/sysv/linux/ttyname.h index cdaf60fb87..48181330a9 100644 --- a/sysdeps/unix/sysv/linux/ttyname.h +++ b/sysdeps/unix/sysv/linux/ttyname.h @@ -34,3 +34,15 @@ 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 + ); +} -- cgit 1.4.1