binder: use cred instead of task for selinux checks

commit 52f88693378a58094c538662ba652aff0253c4fe upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index fe1a70447c1e11da422edb3beabfc40069c61861..f78f7d06ad9fcf4faaccc540e57ac8f8a54569b0 100644 (file)
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -1432,8 +1432,8 @@ static void binder_transaction(struct binder_proc *proc,
                        return_error = BR_FAILED_REPLY;
                        goto err_invalid_target_handle;
                }
-               if (security_binder_transaction(proc->tsk,
-                                               target_proc->tsk) < 0) {
+               if (security_binder_transaction(proc->cred,
+                                               target_proc->cred) < 0) {
                        return_error = BR_FAILED_REPLY;
                        goto err_invalid_target_handle;
                }
@@ -1594,8 +1594,8 @@ static void binder_transaction(struct binder_proc *proc,
                                return_error = BR_FAILED_REPLY;
                                goto err_binder_get_ref_for_node_failed;
                        }
-                       if (security_binder_transfer_binder(proc->tsk,
-                                                           target_proc->tsk)) {
+                       if (security_binder_transfer_binder(proc->cred,
+                                                           target_proc->cred)) {
                                return_error = BR_FAILED_REPLY;
                                goto err_binder_get_ref_for_node_failed;
                        }
@@ -1634,8 +1634,8 @@ static void binder_transaction(struct binder_proc *proc,
                                return_error = BR_FAILED_REPLY;
                                goto err_binder_get_ref_failed;
                        }
-                       if (security_binder_transfer_binder(proc->tsk,
-                                                           target_proc->tsk)) {
+                       if (security_binder_transfer_binder(proc->cred,
+                                                           target_proc->cred)) {
                                return_error = BR_FAILED_REPLY;
                                goto err_binder_get_ref_failed;
                        }
@@ -1698,8 +1698,8 @@ static void binder_transaction(struct binder_proc *proc,
                                return_error = BR_FAILED_REPLY;
                                goto err_fget_failed;
                        }
-                       if (security_binder_transfer_file(proc->tsk,
-                                                         target_proc->tsk,
+                       if (security_binder_transfer_file(proc->cred,
+                                                         target_proc->cred,
                                                          file) < 0) {
                                fput(file);
                                return_error = BR_FAILED_REPLY;
@@ -2781,7 +2781,7 @@ static int binder_ioctl_set_ctx_mgr(struct file *filp)
                ret = -EBUSY;
                goto out;
        }
-       ret = security_binder_set_context_mgr(proc->tsk);
+       ret = security_binder_set_context_mgr(proc->cred);
        if (ret < 0)
                goto out;
        if (uid_valid(binder_context_mgr_uid)) {

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 558adfa5c8a87730f0d0177a1def7570e4883596..53ac461f342bb684a599cf472a659d426782bc64 100644 (file)
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1147,22 +1147,22 @@
  *
  * @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.
- * @binder_transfer_binder
+ *     @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.
- * @binder_transfer_file
+ *     @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
@@ -1332,13 +1332,13 @@
  */
 
 union security_list_options {
-       int (*binder_set_context_mgr)(struct task_struct *mgr);
-       int (*binder_transaction)(struct task_struct *from,
-                                       struct task_struct *to);
-       int (*binder_transfer_binder)(struct task_struct *from,
-                                       struct task_struct *to);
-       int (*binder_transfer_file)(struct task_struct *from,
-                                       struct task_struct *to,
+       int (*binder_set_context_mgr)(const struct cred *mgr);
+       int (*binder_transaction)(const struct cred *from,
+                                       const struct cred *to);
+       int (*binder_transfer_binder)(const struct cred *from,
+                                       const struct cred *to);
+       int (*binder_transfer_file)(const struct cred *from,
+                                       const struct cred *to,
                                        struct file *file);
 
        int (*ptrace_access_check)(struct task_struct *child,

diff --git a/include/linux/security.h b/include/linux/security.h
index c2125e9093e8e51b51662ba8ce4a5faa767710b6..2f5d282bd3ecaf6be99a3fecd86f2902403e8acf 100644 (file)
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -184,13 +184,13 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
 extern int 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,
@@ -394,25 +394,25 @@ static inline int security_init(void)
        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 112df16be770d9b29b12bb44e96c86b00759cb0a..9a13d72a64465777dded12d15d8113d6b4cb7c24 100644 (file)
--- a/security/security.c
+++ b/security/security.c
@@ -131,25 +131,25 @@ int __init security_module_enable(const char *module)
 
 /* 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 a2b63a6a33c7e00c5e9de7cdbb986600f728afa4..607c7fc4f24d310ba4cd9afc6317b5fbaf066da0 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2065,21 +2065,18 @@ static inline u32 open_file_to_av(struct file *file)
 
 /* 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(mysid, mgrsid, SECCLASS_BINDER,
+       return avc_has_perm(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) {
@@ -2093,21 +2090,19 @@ static int selinux_binder_transaction(struct task_struct *from,
                            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(fromsid, tosid, SECCLASS_BINDER, BINDER__TRANSFER,
+       return avc_has_perm(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 = file->f_security;
        struct dentry *dentry = file->f_path.dentry;
        struct inode_security_struct *isec;