write_lock(¤t->fs->lock) guarantees we can't wrongly miss LSM_UNSAFE_SHARE, this is what we care about. Use rcu_read_lock() instead of ->siglock to iterate over the sub-threads. We must see all CLONE_THREAD|CLONE_FS threads which didn't pass exit_fs(), it takes fs->lock too. With or without this patch we can miss the freshly cloned thread and set LSM_UNSAFE_SHARE, we don't care. Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> --- PTRACE/fs/exec.c~2_NO_SIGLOCK 2009-04-24 00:01:53.000000000 +0200 +++ PTRACE/fs/exec.c 2009-04-24 00:36:22.000000000 +0200 @@ -1060,7 +1060,6 @@ EXPORT_SYMBOL(install_exec_creds); int check_unsafe_exec(struct linux_binprm *bprm) { struct task_struct *p = current, *t; - unsigned long flags; unsigned n_fs; int res = 0; @@ -1068,11 +1067,12 @@ int check_unsafe_exec(struct linux_binpr n_fs = 1; write_lock(&p->fs->lock); - lock_task_sighand(p, &flags); + rcu_read_lock(); for (t = next_thread(p); t != p; t = next_thread(t)) { if (t->fs == p->fs) n_fs++; } + rcu_read_lock(); if (p->fs->users > n_fs) { bprm->unsafe |= LSM_UNSAFE_SHARE; @@ -1083,8 +1083,6 @@ int check_unsafe_exec(struct linux_binpr res = 1; } } - - unlock_task_sighand(p, &flags); write_unlock(&p->fs->lock); return res; -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html