BACKPORT: binder: use cred instead of task for selinux checks
Since binder was integrated with selinux, it has passed
'struct task_struct' associated with the binder_proc
to represent the source and target of transactions.
The conversion of task to SID was then done in the hook
implementations. It turns out that there are race conditions
which can result in an incorrect security context being used.
Fix by using the 'struct cred' saved during binder_open and pass
it to the selinux subsystem.
Cc: stable@vger.kernel.org # 5.14 (need backport for earlier stables)
Fixes: 79af73079d75 ("Add security hooks to binder and implement the hooks for SELinux.")
Suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Todd Kjos <tkjos@google.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Bug: 200688826
(cherry picked from commit 52f88693378a58094c538662ba652aff0253c4fe)
[ refactored to avoid changing KMI: struct binder_proc ]
Change-Id: I1664c1f0c2142c17e9ca0d6790bb94de79f531e3
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 9a0b718..052fbff 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2172,7 +2172,8 @@
ret = -EINVAL;
goto done;
}
- if (security_binder_transfer_binder(proc->tsk, target_proc->tsk)) {
+ if (security_binder_transfer_binder(binder_get_cred(proc),
+ binder_get_cred(target_proc))) {
ret = -EPERM;
goto done;
}
@@ -2218,7 +2219,8 @@
proc->pid, thread->pid, fp->handle);
return -EINVAL;
}
- if (security_binder_transfer_binder(proc->tsk, target_proc->tsk)) {
+ if (security_binder_transfer_binder(binder_get_cred(proc),
+ binder_get_cred(target_proc))) {
ret = -EPERM;
goto done;
}
@@ -2306,7 +2308,8 @@
ret = -EBADF;
goto err_fget;
}
- ret = security_binder_transfer_file(proc->tsk, target_proc->tsk, file);
+ ret = security_binder_transfer_file(binder_get_cred(proc),
+ binder_get_cred(target_proc), file);
if (ret < 0) {
ret = -EPERM;
goto err_security;
@@ -2716,8 +2719,8 @@
}
e->to_node = target_node->debug_id;
trace_android_vh_binder_trans(target_proc, proc, thread, tr);
- if (security_binder_transaction(proc->tsk,
- target_proc->tsk) < 0) {
+ if (security_binder_transaction(binder_get_cred(proc),
+ binder_get_cred(target_proc)) < 0) {
return_error = BR_FAILED_REPLY;
return_error_param = -EPERM;
return_error_line = __LINE__;
@@ -4685,7 +4688,7 @@
ret = -EBUSY;
goto out;
}
- ret = security_binder_set_context_mgr(proc->tsk);
+ ret = security_binder_set_context_mgr(binder_get_cred(proc));
if (ret < 0)
goto out;
if (uid_valid(context->binder_context_mgr_uid)) {
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 435a2e2..37dc559 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -26,13 +26,13 @@
* #undef LSM_HOOK
* };
*/
-LSM_HOOK(int, 0, binder_set_context_mgr, struct task_struct *mgr)
-LSM_HOOK(int, 0, binder_transaction, struct task_struct *from,
- struct task_struct *to)
-LSM_HOOK(int, 0, binder_transfer_binder, struct task_struct *from,
- struct task_struct *to)
-LSM_HOOK(int, 0, binder_transfer_file, struct task_struct *from,
- struct task_struct *to, struct file *file)
+LSM_HOOK(int, 0, binder_set_context_mgr, const struct cred *mgr)
+LSM_HOOK(int, 0, binder_transaction, const struct cred *from,
+ const struct cred *to)
+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, 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 3af055b..0ad8aa6 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1297,22 +1297,22 @@
*
* @binder_set_context_mgr:
* Check whether @mgr is allowed to be the binder context manager.
- * @mgr contains the task_struct for the task being registered.
+ * @mgr contains the struct cred for the current binder process.
* Return 0 if permission is granted.
* @binder_transaction:
* Check whether @from is allowed to invoke a binder transaction call
* to @to.
- * @from contains the task_struct for the sending task.
- * @to contains the task_struct for the receiving task.
+ * @from contains the struct cred for the sending process.
+ * @to contains the struct cred for the receiving process.
* @binder_transfer_binder:
* Check whether @from is allowed to transfer a binder reference to @to.
- * @from contains the task_struct for the sending task.
- * @to contains the task_struct for the receiving task.
+ * @from contains the struct cred for the sending process.
+ * @to contains the struct cred for the receiving process.
* @binder_transfer_file:
* Check whether @from is allowed to transfer @file to @to.
- * @from contains the task_struct for the sending task.
+ * @from contains the struct cred for the sending process.
* @file contains the struct file being transferred.
- * @to contains the task_struct for the receiving task.
+ * @to contains the struct cred for the receiving process.
*
* @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 22ef624..83eb9040 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -251,13 +251,13 @@
extern int early_security_init(void);
/* Security operations */
-int security_binder_set_context_mgr(struct task_struct *mgr);
-int security_binder_transaction(struct task_struct *from,
- struct task_struct *to);
-int security_binder_transfer_binder(struct task_struct *from,
- struct task_struct *to);
-int security_binder_transfer_file(struct task_struct *from,
- struct task_struct *to, struct file *file);
+int security_binder_set_context_mgr(const struct cred *mgr);
+int security_binder_transaction(const struct cred *from,
+ const struct cred *to);
+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_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,
@@ -493,25 +493,25 @@
return 0;
}
-static inline int security_binder_set_context_mgr(struct task_struct *mgr)
+static inline int security_binder_set_context_mgr(const struct cred *mgr)
{
return 0;
}
-static inline int security_binder_transaction(struct task_struct *from,
- struct task_struct *to)
+static inline int security_binder_transaction(const struct cred *from,
+ const struct cred *to)
{
return 0;
}
-static inline int security_binder_transfer_binder(struct task_struct *from,
- struct task_struct *to)
+static inline int security_binder_transfer_binder(const struct cred *from,
+ const struct cred *to)
{
return 0;
}
-static inline int security_binder_transfer_file(struct task_struct *from,
- struct task_struct *to,
+static inline int security_binder_transfer_file(const struct cred *from,
+ const struct cred *to,
struct file *file)
{
return 0;
diff --git a/security/security.c b/security/security.c
index cf8ddca..1e0f79c 100644
--- a/security/security.c
+++ b/security/security.c
@@ -689,25 +689,25 @@
/* Security operations */
-int security_binder_set_context_mgr(struct task_struct *mgr)
+int security_binder_set_context_mgr(const struct cred *mgr)
{
return call_int_hook(binder_set_context_mgr, 0, mgr);
}
-int security_binder_transaction(struct task_struct *from,
- struct task_struct *to)
+int security_binder_transaction(const struct cred *from,
+ const struct cred *to)
{
return call_int_hook(binder_transaction, 0, from, to);
}
-int security_binder_transfer_binder(struct task_struct *from,
- struct task_struct *to)
+int security_binder_transfer_binder(const struct cred *from,
+ const struct cred *to)
{
return call_int_hook(binder_transfer_binder, 0, from, to);
}
-int security_binder_transfer_file(struct task_struct *from,
- struct task_struct *to, struct file *file)
+int security_binder_transfer_file(const struct cred *from,
+ const struct cred *to, struct file *file)
{
return call_int_hook(binder_transfer_file, 0, from, to, file);
}
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index a490c84..0a18cbc 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2007,22 +2007,19 @@
/* Hook functions begin here. */
-static int selinux_binder_set_context_mgr(struct task_struct *mgr)
+static int selinux_binder_set_context_mgr(const struct cred *mgr)
{
- u32 mysid = current_sid();
- u32 mgrsid = task_sid(mgr);
-
return avc_has_perm(&selinux_state,
- mysid, mgrsid, SECCLASS_BINDER,
+ current_sid(), cred_sid(mgr), SECCLASS_BINDER,
BINDER__SET_CONTEXT_MGR, NULL);
}
-static int selinux_binder_transaction(struct task_struct *from,
- struct task_struct *to)
+static int selinux_binder_transaction(const struct cred *from,
+ const struct cred *to)
{
u32 mysid = current_sid();
- u32 fromsid = task_sid(from);
- u32 tosid = task_sid(to);
+ u32 fromsid = cred_sid(from);
+ u32 tosid = cred_sid(to);
int rc;
if (mysid != fromsid) {
@@ -2033,27 +2030,24 @@
return rc;
}
- return avc_has_perm(&selinux_state,
- fromsid, tosid, SECCLASS_BINDER, BINDER__CALL,
- NULL);
+ return avc_has_perm(&selinux_state, fromsid, tosid,
+ SECCLASS_BINDER, BINDER__CALL, NULL);
}
-static int selinux_binder_transfer_binder(struct task_struct *from,
- struct task_struct *to)
+static int selinux_binder_transfer_binder(const struct cred *from,
+ const struct cred *to)
{
- u32 fromsid = task_sid(from);
- u32 tosid = task_sid(to);
-
return avc_has_perm(&selinux_state,
- fromsid, tosid, SECCLASS_BINDER, BINDER__TRANSFER,
+ cred_sid(from), cred_sid(to),
+ SECCLASS_BINDER, BINDER__TRANSFER,
NULL);
}
-static int selinux_binder_transfer_file(struct task_struct *from,
- struct task_struct *to,
+static int selinux_binder_transfer_file(const struct cred *from,
+ const struct cred *to,
struct file *file)
{
- u32 sid = task_sid(to);
+ u32 sid = cred_sid(to);
struct file_security_struct *fsec = selinux_file(file);
struct dentry *dentry = file->f_path.dentry;
struct inode_security_struct *isec;
