Messages in this thread Patch in this message | | | Subject | Re: How to lock current->signal->tty | From | Stephen Smalley <> | Date | Tue, 08 Aug 2006 13:11:54 -0400 |
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On Tue, 2006-08-08 at 16:17 +0100, Alan Cox wrote: > The biggest crawly horror I've found so far in auditing the tty locking > is current->signal->tty. The tty layer currently and explicitly protects > this using tty_mutex. The core kernel likewise knows about this. > > Unfortunately: > SELinux doesn't do any locking at all > Dquot passes the tty to tty_write_message without locking > audit_log_exit doesn't do any locking at all > acct.c thinks tasklist_lock protects it (wrong) > drivers/char/sx misuses it unlocked in debug info > fs/proc/array thinks tasklist_lock will save it (also wrong) > fs3270 does fascinating things with it which don't look safe > ebtables remote debugging (#if 0 thankfully) does no locking > and just for fun calls the tty driver directly with no > driver locking either. > voyager_thread sets up a thread and then touches ->tty unlocked > (and it seems daemonize already fixed it) > Sparc solaris_procids sets it to NULL without locking > arch/ia64/kernel/unanligned seems to write to it without locking > arch/um/kernel/exec.c appears to believe task_lock is used > > The semantics are actually as follows > > signal->tty must not be changed without holding tty_mutex > signal->tty must not be used unless tty_mutex is held from before > reading it to completing using it > Simple if(signal->tty == NULL) type checks are ok > > I'm looking longer term at tty ref counting and the like but for now and > current distributions it might be an idea to fix the existing problems.
Does this look sane? Or do we need a common helper factored from disassociate_ctty()? Why is the locking different for TIOCNOTTY in the non-leader case?
---
selinux: fix tty locking
Take tty_mutex when accessing ->signal->tty. Noted by Alan Cox.
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
---
security/selinux/hooks.c | 5 ++++- 1 files changed, 4 insertions(+), 1 deletion(-)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 5d1b8c7..4b0f904 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -1711,10 +1711,12 @@ static inline void flush_unauthorized_fi { struct avc_audit_data ad; struct file *file, *devnull = NULL; - struct tty_struct *tty = current->signal->tty; + struct tty_struct *tty; struct fdtable *fdt; long j = -1; + mutex_lock(&tty_mutex); + tty = current->signal->tty; if (tty) { file_list_lock(); file = list_entry(tty->tty_files.next, typeof(*file), f_u.fu_list); @@ -1734,6 +1736,7 @@ static inline void flush_unauthorized_fi } file_list_unlock(); } + mutex_unlock(&tty_mutex); /* Revalidate access to inherited open files. */
-- Stephen Smalley National Security Agency
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