Re: [PATCH v2 3/3] selinux: require PROCESS__PTRACE for FOLL_FORCE introspection

[Paul Moore <paul@paul-moore.com>]

On Aug 25, 2026 Jann Horn <jannh@google.com> wrote:
> 
> On systems configured with PROC_MEM_FORCE_ALWAYS, ensure that a process can
> only create anonymous executable memory via /proc/self/mem if it has
> PROCESS__PTRACE (like when using /proc/$pid/mem of another process).
> 
> This closes a hole in code integrity enforcement that Project Zero has used
> in a remote Android exploit chain:
> It was possible to use a memory corruption bug in a service without
> EXECMEM/EXECMOD/PTRACE permission to overwrite executable code via
> /proc/self/mem, which made it possible to load and run shellcode containing
> a kernel exploit.
> 
> Signed-off-by: Jann Horn <jannh@google.com>
> Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com>
> Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
> ---
>  security/selinux/hooks.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 18dd28b2bb13..2c2c60e9e0fe 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2157,6 +2157,27 @@ static int selinux_ptrace_traceme(struct task_struct *parent)
>  			    SECCLASS_PROCESS, PROCESS__PTRACE, NULL);
>  }
>  
> +/*
> + * Decide whether it should be possible to read non-readable VMAs and write
> + * non-writable VMAs via /proc/self/mem.
> + * This only applies to systems configured with PROC_MEM_FORCE_ALWAYS, and only
> + * triggers on accesses that are not visible to selinux_ptrace_access_check()
> + * because of the introspection exceptions in may_access_mm() and
> + * __ptrace_may_access().
> + *
> + * This allows a process to overwrite read-only code in its own address space.
> + *
> + * Creating an audit record on denial doesn't make sense here, since we can't
> + * tell whether FOLL_FORCE matters for the accessed VMAs.
> + */
> +static int selinux_mem_foll_force_opened_by_owner(const struct cred *subject)
> +{
> +	struct av_decision avd;
> +	u32 sid = cred_sid(subject);
> +
> +	return avc_has_perm_noaudit(sid, sid, SECCLASS_PROCESS, PROCESS__PTRACE, 0, &avd);
> +}

I realize not all of the SELinux hook callbacks use proper kdoc comments,
but I'm trying to fix that.  If you could make this a kdoc function header
comment I would appreciate it.

--
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