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

[Lorenzo Stoakes (ARM)]

On Tue, Aug 25, 2026 at 08:39:19PM +0200, Jann Horn 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 at google.com>

Not really my area but in general looks reasonable so:

Acked-by: Lorenzo Stoakes (ARM) <ljs at 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);
> +}
> +
>  static int selinux_capget(const struct task_struct *target, kernel_cap_t *effective,
>  			  kernel_cap_t *inheritable, kernel_cap_t *permitted)
>  {
> @@ -7558,6 +7579,7 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
>
>  	LSM_HOOK_INIT(ptrace_access_check, selinux_ptrace_access_check),
>  	LSM_HOOK_INIT(ptrace_traceme, selinux_ptrace_traceme),
> +	LSM_HOOK_INIT(mem_foll_force_opened_by_owner, selinux_mem_foll_force_opened_by_owner),
>  	LSM_HOOK_INIT(capget, selinux_capget),
>  	LSM_HOOK_INIT(capset, selinux_capset),
>  	LSM_HOOK_INIT(capable, selinux_capable),
>
> --
> 2.55.0.860.g4b6b3295ed-goog
>

--
Cheers, Lorenzo