I have read through the code in exec_mmap and I do not see anything that depends on sighand or the sighand lock, or on signals in anyway so this should be safe.

This rearrangement of code has two significant benefits. It makes the determination of passing the point of no return by testing bprm->mm accurate. All failures prior to that point in flush_old_exec are either truly recoverable or they are fatal.

Further this consolidates all of the possible indefinite waits for userspace together at the top of flush_old_exec. The possible wait for a ptracer on PTRACE_EVENT_EXIT, the possible wait for a page fault to be resolved in clear_child_tid, and the possible wait for a page fault in exit_robust_list.

This consolidation allows the creation of a mutex to replace cred_guard_mutex that is not held over possible indefinite userspace waits. Which will allow removing deadlock scenarios from the kernel.

Signed-off-by: "Eric W. Biederman" ebiederm@xmission.com Reviewed-by: Bernd Edlinger bernd.edlinger@hotmail.de Reviewed-by: Kees Cook keescook@chromium.org Reviewed-by: Kirill Tkhai ktkhai@virtuozzo.com --- fs/exec.c | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c index 215d86f7..d820a72 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1272,18 +1272,6 @@ int flush_old_exec(struct linux_binprm * bprm) if (retval) goto out;

-#ifdef CONFIG_POSIX_TIMERS - exit_itimers(me->signal); - flush_itimer_signals(); -#endif - - /* - * Make the signal table private. - */ - retval = unshare_sighand(me); - if (retval) - goto out; - /* * Must be called _before_ exec_mmap() as bprm->mm is * not visibile until then. This also enables the update @@ -1307,6 +1295,18 @@ int flush_old_exec(struct linux_binprm * bprm) */ bprm->mm = NULL;

+#ifdef CONFIG_POSIX_TIMERS + exit_itimers(me->signal); + flush_itimer_signals(); +#endif + + /* + * Make the signal table private. + */ + retval = unshare_sighand(me); + if (retval) + goto out; + set_fs(USER_DS); me->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD | PF_NOFREEZE | PF_NO_SETAFFINITY);