[PATCH v2 4/4] security: binder: Add binder object flags to selinux_binder_transfer_file

T.J. Mercier
2023-01-23T19:17:26Z

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, so the binder object
flags are added to the security_binder_transfer_file hook so that LSMs
can enforce restrictions on charge transfers.

Signed-off-by: T.J. Mercier <tjmercier-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
---
drivers/android/binder.c | 2 +-
include/linux/lsm_hook_defs.h | 2 +-
include/linux/lsm_hooks.h | 5 ++++-
include/linux/security.h | 6 ++++--
security/security.c | 4 ++--
security/selinux/hooks.c | 13 ++++++++++++-
security/selinux/include/classmap.h | 2 +-
7 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 5e707974793f..7b1bb23b6b79 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2270,7 +2270,7 @@ static int binder_translate_fd(u32 fd, binder_size_t fd_offset, __u32 flags,
ret = -EBADF;
goto err_fget;
}
- ret = security_binder_transfer_file(proc->cred, target_proc->cred, file);
+ ret = security_binder_transfer_file(proc->cred, target_proc->cred, file, flags);
if (ret < 0) {
ret = -EPERM;
goto err_security;
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index ed6cb2ac55fa..84ee61089f7b 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -32,7 +32,7 @@ LSM_HOOK(int, 0, binder_transaction, const struct cred *from,
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)
+ const struct cred *to, struct file *file, u32 binder_object_flags)
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..d57977336ae8 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1381,9 +1381,12 @@
* Return 0 if permission is granted.
* @binder_transfer_file:
* Check whether @from is allowed to transfer @file to @to.
+ * If @binder_object_flags indicates a memory charge transfer for @file, then
+ * permission for the charge transfer can be checked as well.
* @from contains the struct cred for the sending process.
- * @file contains the struct file being transferred.
* @to contains the struct cred for the receiving process.
+ * @file contains the struct file being transferred.
+ * @binder_object_flags contains the flags associated with the binder object.
* Return 0 if permission is granted.
*
* @ptrace_access_check:
diff --git a/include/linux/security.h b/include/linux/security.h
index 5b67f208f7de..c4b80fc8d104 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -269,7 +269,8 @@ int security_binder_transaction(const struct cred *from,
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);
+ const struct cred *to, struct file *file,
+ u32 binder_object_flags);
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,
@@ -542,7 +543,8 @@ static inline int security_binder_transfer_binder(const struct cred *from,

static inline int security_binder_transfer_file(const struct cred *from,
const struct cred *to,
- struct file *file)
+ struct file *file,
+ u32 binder_object_flags)
{
return 0;
}
diff --git a/security/security.c b/security/security.c
index d1571900a8c7..12ccaca744c0 100644
--- a/security/security.c
+++ b/security/security.c
@@ -796,9 +796,9 @@ int security_binder_transfer_binder(const struct cred *from,
}

int security_binder_transfer_file(const struct cred *from,
- const struct cred *to, struct file *file)
+ const struct cred *to, struct file *file, u32 binder_object_flags)
{
- return call_int_hook(binder_transfer_file, 0, from, to, file);
+ return call_int_hook(binder_transfer_file, 0, from, to, file, binder_object_flags);
}

int security_ptrace_access_check(struct task_struct *child, unsigned int mode)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 3c5be76a9199..d4cfca3c9a3b 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -88,6 +88,7 @@
#include <linux/bpf.h>
#include <linux/kernfs.h>
#include <linux/stringhash.h> /* for hashlen_string() */
+#include <uapi/linux/android/binder.h>
#include <uapi/linux/mount.h>
#include <linux/fsnotify.h>
#include <linux/fanotify.h>
@@ -2029,7 +2030,8 @@ static int selinux_binder_transfer_binder(const struct cred *from,

static int selinux_binder_transfer_file(const struct cred *from,
const struct cred *to,
- struct file *file)
+ struct file *file,
+ u32 binder_object_flags)
{
u32 sid = cred_sid(to);
struct file_security_struct *fsec = selinux_file(file);
@@ -2038,6 +2040,15 @@ static int selinux_binder_transfer_file(const struct cred *from,
struct common_audit_data ad;
int rc;

+ if (binder_object_flags & BINDER_FD_FLAG_XFER_CHARGE) {
+ rc = avc_has_perm(&selinux_state,
+ cred_sid(from), sid,
+ SECCLASS_BINDER, BINDER__TRANSFER_CHARGE,
+ NULL);
+ if (rc)
+ return rc;
+ }
+
ad.type = LSM_AUDIT_DATA_PATH;
ad.u.path = file->f_path;

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",
--
2.39.0.246.g2a6d74b583-goog