On Tue, Jul 14, 2020 at 08:30:02AM -0500, Eric W. Biederman wrote: > > Currently it is necessary for the usermode helper code and the code that > launches init to use set_fs so that pages coming from the kernel look like > they are coming from userspace. > > To allow that usage of set_fs to be removed cleanly the argument copying > from userspace needs to happen earlier. Move the allocation and > initialization of bprm->mm into alloc_bprm so that the bprm->mm is > available early to store the new user stack into. This is a prerequisite > for copying argv and envp into the new user stack early before ther rest of > exec. > > To keep the things consistent the cleanup of bprm->mm is moved into > free_bprm. So that bprm->mm will be cleaned up whenever bprm->mm is > allocated and free_bprm are called. > > Moving bprm_mm_init earlier is safe as it does not depend on any files, > current->in_execve, current->fs->in_exec, bprm->unsafe, or the if the file > table is shared. (AKA bprm_mm_init does not depend on any of the code that > happens between alloc_bprm and where it was previously called.) > > This moves bprm->mm cleanup after current->fs->in_exec is set to 0. This > is safe because current->fs->in_exec is only used to preventy taking an > additional reference on the fs_struct. > > This moves bprm->mm cleanup after current->in_execve is set to 0. This is > safe because current->in_execve is only used by the lsms (apparmor and > tomoyou) and always for LSM specific functions, never for anything to do > with the mm. > > This adds bprm->mm cleanup into the successful return path. This is safe > because being on the successful return path implies that begin_new_exec > succeeded and set brpm->mm to NULL. As bprm->mm is NULL bprm cleanup I am > moving into free_bprm will do nothing. > > Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> This looks correct, and is required before moving the arg pages stuff, so good. :) -- Kees Cook
