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SubjectRe: [PATCH 5/7] exec: Factor bprm_execve out of do_execve_common
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@xmission.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

--
Kees Cook

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