On Tue, Jul 14, 2020 at 08:30:30AM -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. Factor bprm_execve > out of do_execve_common to separate out the copying of arguments > to the newe stack, and the rest of exec. > > In separating bprm_execve from do_execve_common the copying > of the arguments onto the new stack happens earlier. > > As the copying of the arguments does not depend any security hooks, > files, the file table, current->in_execve, current->fs->in_exec, > bprm->unsafe, or creds this is safe. > > Likewise the security hook security_creds_for_exec does not depend upon > preventing the argument copying from happening. > > In addition to making it possible to implement kernel_execve that > performs the copying differently, this separation of bprm_execve from > do_execve_common makes for a nice separation of responsibilities making > the exec code easier to navigate. > > Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -- Kees Cook
