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 332b4a2cbb948876be27c4d4220d31efd467d158..c5fd7908fc9135938d5c4a4fcbb3e1c0959d4eff 100644 (file)
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2285,7 +2285,7 @@ static int binder_translate_binder(struct flat_binder_object *fp,
                ret = -EINVAL;
                goto done;
        }
-       if (security_binder_transfer_binder(proc->tsk, target_proc->tsk)) {
+       if (security_binder_transfer_binder(proc->cred, target_proc->cred)) {
                ret = -EPERM;
                goto done;
        }
@@ -2331,7 +2331,7 @@ static int binder_translate_handle(struct flat_binder_object *fp,
                                  proc->pid, thread->pid, fp->handle);
                return -EINVAL;
        }
-       if (security_binder_transfer_binder(proc->tsk, target_proc->tsk)) {
+       if (security_binder_transfer_binder(proc->cred, target_proc->cred)) {
                ret = -EPERM;
                goto done;
        }
@@ -2415,7 +2415,7 @@ static int binder_translate_fd(int fd,
                ret = -EBADF;
                goto err_fget;
        }
-       ret = security_binder_transfer_file(proc->tsk, target_proc->tsk, file);
+       ret = security_binder_transfer_file(proc->cred, target_proc->cred, file);
        if (ret < 0) {
                ret = -EPERM;
                goto err_security;
@@ -2802,8 +2802,8 @@ static void binder_transaction(struct binder_proc *proc,
                        return_error_line = __LINE__;
                        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;
                        return_error_param = -EPERM;
                        return_error_line = __LINE__;
@@ -4469,7 +4469,7 @@ 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(context->binder_context_mgr_uid)) {

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index c9258124e41757187cdb8b2f83c5901966345902..569debc49f3d74541f87f5a37912fef1c51922bf 100644 (file)
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1170,22 +1170,22 @@
  *
  * @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
@@ -1353,13 +1353,13 @@
  *     @ctxlen points to the place to put the length of @ctx.
  */
 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 dab093af4ee8dabba9208eefefdac9482b941b65..1c8968a267c2b14d933cfa4e0d9e11e7fddf39a0 100644 (file)
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -197,13 +197,13 @@ 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,
@@ -424,25 +424,25 @@ 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 4fbe4e495c0211f6de4ca4712d1cc3a04b48e818..737a5985343cdc60cc96ee8aba56c96fdad93b3c 100644 (file)
--- a/security/security.c
+++ b/security/security.c
@@ -222,25 +222,25 @@ EXPORT_SYMBOL(unregister_lsm_notifier);
 
 /* 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 895d369bc4103faa9fb2b51accd456ade20d1c1d..9bb1d492f70472490c796432fc5f680bd9f5593d 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2136,21 +2136,18 @@ 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) {
@@ -2164,21 +2161,19 @@ 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;