On Mon, Jan 9, 2023 at 2:28 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote: > > On 1/9/2023 1:38 PM, T.J. Mercier wrote: > > Any process can cause a memory charge transfer to occur to any other > > process when transmitting a file descriptor through binder. This should > > only be possible for central allocator processes, > > How is a "central allocator process" identified? Any process with the transfer_charge permission. On Android this is the graphics allocator HAL which would have this added to its policy. > If I have a LSM that > is not SELinux (e.g. AppArmor, Smack) or no LSM at all, how can/should this > be enforced? Sorry, why would you be expecting enforcement with no LSM? Are you suggesting that this check should be different than the ones that already exist for Binder here? https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/lsm_hook_defs.h#n29 > Why isn't binder enforcing this restriction itself? Binder has no direct knowledge of which process has been designated as an allocator / charge transferrer. That is defined externally by whoever configures the system. > > so a new SELinux > > permission is added to restrict which processes are allowed to initiate > > these charge transfers. > > Which is all perfectly reasonable if you have SELinux. > > > > > Signed-off-by: T.J. Mercier <tjmercier@xxxxxxxxxx> > > --- > > drivers/android/binder.c | 5 +++++ > > include/linux/lsm_hook_defs.h | 2 ++ > > include/linux/lsm_hooks.h | 6 ++++++ > > include/linux/security.h | 2 ++ > > security/security.c | 6 ++++++ > > security/selinux/hooks.c | 9 +++++++++ > > security/selinux/include/classmap.h | 2 +- > > 7 files changed, 31 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/android/binder.c b/drivers/android/binder.c > > index 9830848c8d25..9063db04826d 100644 > > --- a/drivers/android/binder.c > > +++ b/drivers/android/binder.c > > @@ -2279,6 +2279,11 @@ static int binder_translate_fd(u32 fd, binder_size_t fd_offset, __u32 flags, > > if (IS_ENABLED(CONFIG_MEMCG) && (flags & BINDER_FD_FLAG_XFER_CHARGE)) { > > struct dma_buf *dmabuf; > > > > + if (security_binder_transfer_charge(proc->cred, target_proc->cred)) { > > + ret = -EPERM; > > + goto err_security; > > + } > > + > > if (unlikely(!is_dma_buf_file(file))) { > > binder_user_error( > > "%d:%d got transaction with XFER_CHARGE for non-dmabuf fd, %d\n", > > diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h > > index ed6cb2ac55fa..8db2a958557e 100644 > > --- a/include/linux/lsm_hook_defs.h > > +++ b/include/linux/lsm_hook_defs.h > > @@ -33,6 +33,8 @@ LSM_HOOK(int, 0, binder_transfer_binder, const struct cred *from, > > const struct cred *to) > > LSM_HOOK(int, 0, binder_transfer_file, const struct cred *from, > > const struct cred *to, struct file *file) > > +LSM_HOOK(int, 0, binder_transfer_charge, const struct cred *from, > > + const struct cred *to) > > LSM_HOOK(int, 0, ptrace_access_check, struct task_struct *child, > > unsigned int mode) > > LSM_HOOK(int, 0, ptrace_traceme, struct task_struct *parent) > > diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h > > index 0a5ba81f7367..39c40c7bf519 100644 > > --- a/include/linux/lsm_hooks.h > > +++ b/include/linux/lsm_hooks.h > > @@ -1385,6 +1385,12 @@ > > * @file contains the struct file being transferred. > > * @to contains the struct cred for the receiving process. > > * Return 0 if permission is granted. > > + * @binder_transfer_charge: > > + * Check whether @from is allowed to transfer the memory charge for a > > + * buffer out of its cgroup to @to. > > + * @from contains the struct cred for the sending process. > > + * @to contains the struct cred for the receiving process. > > + * Return 0 if permission is granted. > > * > > * @ptrace_access_check: > > * Check permission before allowing the current process to trace the > > diff --git a/include/linux/security.h b/include/linux/security.h > > index 5b67f208f7de..3b7472308430 100644 > > --- a/include/linux/security.h > > +++ b/include/linux/security.h > > @@ -270,6 +270,8 @@ int security_binder_transfer_binder(const struct cred *from, > > const struct cred *to); > > int security_binder_transfer_file(const struct cred *from, > > const struct cred *to, struct file *file); > > +int security_binder_transfer_charge(const struct cred *from, > > + const struct cred *to); > > int security_ptrace_access_check(struct task_struct *child, unsigned int mode); > > int security_ptrace_traceme(struct task_struct *parent); > > int security_capget(struct task_struct *target, > > diff --git a/security/security.c b/security/security.c > > index d1571900a8c7..97e1e74d1ff2 100644 > > --- a/security/security.c > > +++ b/security/security.c > > @@ -801,6 +801,12 @@ int security_binder_transfer_file(const struct cred *from, > > return call_int_hook(binder_transfer_file, 0, from, to, file); > > } > > > > +int security_binder_transfer_charge(const struct cred *from, > > + const struct cred *to) > > +{ > > + return call_int_hook(binder_transfer_charge, 0, from, to); > > +} > > + > > int security_ptrace_access_check(struct task_struct *child, unsigned int mode) > > { > > return call_int_hook(ptrace_access_check, 0, child, mode); > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > > index 3c5be76a9199..823ef14924bd 100644 > > --- a/security/selinux/hooks.c > > +++ b/security/selinux/hooks.c > > @@ -2066,6 +2066,14 @@ static int selinux_binder_transfer_file(const struct cred *from, > > &ad); > > } > > > > +static int selinux_binder_transfer_charge(const struct cred *from, const struct cred *to) > > +{ > > + return avc_has_perm(&selinux_state, > > + cred_sid(from), cred_sid(to), > > + SECCLASS_BINDER, BINDER__TRANSFER_CHARGE, > > + NULL); > > +} > > + > > static int selinux_ptrace_access_check(struct task_struct *child, > > unsigned int mode) > > { > > @@ -7052,6 +7060,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = { > > LSM_HOOK_INIT(binder_transaction, selinux_binder_transaction), > > LSM_HOOK_INIT(binder_transfer_binder, selinux_binder_transfer_binder), > > LSM_HOOK_INIT(binder_transfer_file, selinux_binder_transfer_file), > > + LSM_HOOK_INIT(binder_transfer_charge, selinux_binder_transfer_charge), > > > > LSM_HOOK_INIT(ptrace_access_check, selinux_ptrace_access_check), > > LSM_HOOK_INIT(ptrace_traceme, selinux_ptrace_traceme), > > diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h > > index a3c380775d41..2eef180d10d7 100644 > > --- a/security/selinux/include/classmap.h > > +++ b/security/selinux/include/classmap.h > > @@ -172,7 +172,7 @@ const struct security_class_mapping secclass_map[] = { > > { "tun_socket", > > { COMMON_SOCK_PERMS, "attach_queue", NULL } }, > > { "binder", { "impersonate", "call", "set_context_mgr", "transfer", > > - NULL } }, > > + "transfer_charge", NULL } }, > > { "cap_userns", > > { COMMON_CAP_PERMS, NULL } }, > > { "cap2_userns",
