Staging: binder: Keep a reference to the files_struct while the driver is mmapped

This prevents breaking fget_light if a single threaded application
allows incoming file descriptors (in replies or on nodes).
Should also prevent inserting a file in the wrong files_struct if the
receving process execs in the middle of a transaction (between
task_get_unused_fd_flags and task_fd_install).

Signed-off-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 63 insertions, 16 deletions

diff --git a/drivers/staging/android/binder.c b/drivers/staging/android/binder.c
index 64f95ee8a704..09962e87c600 100644
--- a/drivers/staging/android/binder.c
+++ b/drivers/staging/android/binder.c
@@ -41,6 +41,8 @@ static int binder_last_id;
 static struct proc_dir_entry *binder_proc_dir_entry_root;
 static struct proc_dir_entry *binder_proc_dir_entry_proc;
 static struct hlist_head binder_dead_nodes;
+static HLIST_HEAD(binder_release_files_list);
+static DEFINE_MUTEX(binder_release_files_lock);
 
 static int binder_read_proc_proc(
         char *page, char **start, off_t off, int count, int *eof, void *data);
@@ -241,6 +243,8 @@ struct binder_proc {
         int pid;
         struct vm_area_struct *vma;
         struct task_struct *tsk;
+        struct files_struct *files;
+        struct hlist_node release_files_node;
         void *buffer;
         size_t user_buffer_offset;
 
@@ -309,9 +313,9 @@ struct binder_transaction {
 /*
  * copied from get_unused_fd_flags
  */
-int task_get_unused_fd_flags(struct task_struct *tsk, int flags)
+int task_get_unused_fd_flags(struct binder_proc *proc, int flags)
 {
-        struct files_struct *files = get_files_struct(tsk);
+        struct files_struct *files = proc->files;
         int fd, error;
         struct fdtable *fdt;
         unsigned long rlim_cur;
@@ -333,9 +337,9 @@ repeat:
          * will limit the total number of files that can be opened.
          */
         rlim_cur = 0;
-        if (lock_task_sighand(tsk, &irqs)) {
-                rlim_cur = tsk->signal->rlim[RLIMIT_NOFILE].rlim_cur;
-                unlock_task_sighand(tsk, &irqs);
+        if (lock_task_sighand(proc->tsk, &irqs)) {
+                rlim_cur = proc->tsk->signal->rlim[RLIMIT_NOFILE].rlim_cur;
+                unlock_task_sighand(proc->tsk, &irqs);
         }
         if (fd >= rlim_cur)
                 goto out;
@@ -371,7 +375,6 @@ repeat:
 
 out:
         spin_unlock(&files->file_lock);
-        put_files_struct(files);
         return error;
 }
 
@@ -379,9 +382,9 @@ out:
  * copied from fd_install
  */
 static void task_fd_install(
-        struct task_struct *tsk, unsigned int fd, struct file *file)
+        struct binder_proc *proc, unsigned int fd, struct file *file)
 {
-        struct files_struct *files = get_files_struct(tsk);
+        struct files_struct *files = proc->files;
         struct fdtable *fdt;
 
         if (files == NULL)
@@ -392,7 +395,6 @@ static void task_fd_install(
         BUG_ON(fdt->fd[fd] != NULL);
         rcu_assign_pointer(fdt->fd[fd], file);
         spin_unlock(&files->file_lock);
-        put_files_struct(files);
 }
 
 /*
@@ -409,10 +411,10 @@ static void __put_unused_fd(struct files_struct *files, unsigned int fd)
 /*
  * copied from sys_close
  */
-static long task_close_fd(struct task_struct *tsk, unsigned int fd)
+static long task_close_fd(struct binder_proc *proc, unsigned int fd)
 {
         struct file *filp;
-        struct files_struct *files = get_files_struct(tsk);
+        struct files_struct *files = proc->files;
         struct fdtable *fdt;
         int retval;
 
@@ -439,12 +441,10 @@ static long task_close_fd(struct task_struct *tsk, unsigned int fd)
                      retval == -ERESTART_RESTARTBLOCK))
                 retval = -EINTR;
 
-        put_files_struct(files);
         return retval;
 
 out_unlock:
         spin_unlock(&files->file_lock);
-        put_files_struct(files);
         return -EBADF;
 }
 
@@ -1549,13 +1549,13 @@ binder_transaction(struct binder_proc *proc, struct binder_thread *thread,
                                 return_error = BR_FAILED_REPLY;
                                 goto err_fget_failed;
                         }
-                        target_fd = task_get_unused_fd_flags(target_proc->tsk, O_CLOEXEC);
+                        target_fd = task_get_unused_fd_flags(target_proc, O_CLOEXEC);
                         if (target_fd < 0) {
                                 fput(file);
                                 return_error = BR_FAILED_REPLY;
                                 goto err_get_unused_fd_failed;
                         }
-                        task_fd_install(target_proc->tsk, target_fd, file);
+                        task_fd_install(target_proc, target_fd, file);
                         if (binder_debug_mask & BINDER_DEBUG_TRANSACTION)
                                 printk(KERN_INFO "        fd %ld -> %d\n", fp->handle, target_fd);
                         /* TODO: fput? */
@@ -1698,7 +1698,7 @@ binder_transaction_buffer_release(struct binder_proc *proc, struct binder_buffer
                         if (binder_debug_mask & BINDER_DEBUG_TRANSACTION)
                                 printk(KERN_INFO "        fd %ld\n", fp->handle);
                         if (failed_at)
-                                task_close_fd(proc->tsk, fp->handle);
+                                task_close_fd(proc, fp->handle);
                         break;
 
                 default:
@@ -2663,6 +2663,34 @@ static void binder_vma_open(struct vm_area_struct *vma)
                         (unsigned long)pgprot_val(vma->vm_page_prot));
         dump_stack();
 }
+
+static void binder_release_files(struct work_struct *work)
+{
+        struct binder_proc *proc;
+        struct files_struct *files;
+        do {
+                mutex_lock(&binder_lock);
+                mutex_lock(&binder_release_files_lock);
+                if (!hlist_empty(&binder_release_files_list)) {
+                        proc = hlist_entry(binder_release_files_list.first,
+                                        struct binder_proc, release_files_node);
+                        hlist_del_init(&proc->release_files_node);
+                        files = proc->files;
+                        if (files)
+                                proc->files = NULL;
+                } else {
+                        proc = NULL;
+                        files = NULL;
+                }
+                mutex_unlock(&binder_release_files_lock);
+                mutex_unlock(&binder_lock);
+                if (files)
+                        put_files_struct(files);
+        } while (proc);
+}
+
+static DECLARE_WORK(binder_release_files_work, binder_release_files);
+
 static void binder_vma_close(struct vm_area_struct *vma)
 {
         struct binder_proc *proc = vma->vm_private_data;
@@ -2673,6 +2701,13 @@ static void binder_vma_close(struct vm_area_struct *vma)
                         (vma->vm_end - vma->vm_start) / SZ_1K, vma->vm_flags,
                         (unsigned long)pgprot_val(vma->vm_page_prot));
         proc->vma = NULL;
+        mutex_lock(&binder_release_files_lock);
+        if (proc->files) {
+                hlist_add_head(&proc->release_files_node,
+                                &binder_release_files_list);
+                schedule_work(&binder_release_files_work);
+        }
+        mutex_unlock(&binder_release_files_lock);
 }
 
 static struct vm_operations_struct binder_vm_ops = {
@@ -2751,6 +2786,7 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
         binder_insert_free_buffer(proc, buffer);
         proc->free_async_space = proc->buffer_size / 2;
         barrier();
+        proc->files = get_files_struct(current);
         proc->vma = vma;
 
         /*printk(KERN_INFO "binder_mmap: %d %lx-%lx maps %p\n", proc->pid, vma->vm_start, vma->vm_end, proc->buffer);*/
@@ -2831,6 +2867,7 @@ static int binder_release(struct inode *nodp, struct file *filp)
         struct hlist_node *pos;
         struct binder_transaction *t;
         struct rb_node *n;
+        struct files_struct *files;
         struct binder_proc *proc = filp->private_data;
         int threads, nodes, incoming_refs, outgoing_refs, buffers, active_transactions, page_count;
 
@@ -2840,6 +2877,14 @@ static int binder_release(struct inode *nodp, struct file *filp)
                 remove_proc_entry(strbuf, binder_proc_dir_entry_proc);
         }
         mutex_lock(&binder_lock);
+        mutex_lock(&binder_release_files_lock);
+        if (!hlist_unhashed(&proc->release_files_node))
+                hlist_del(&proc->release_files_node);
+        files = proc->files;
+        if (files)
+                proc->files = NULL;
+        mutex_unlock(&binder_release_files_lock);
+
         hlist_del(&proc->proc_node);
         if (binder_context_mgr_node && binder_context_mgr_node->proc == proc) {
                 if (binder_debug_mask & BINDER_DEBUG_DEAD_BINDER)
@@ -2937,6 +2982,8 @@ static int binder_release(struct inode *nodp, struct file *filp)
                        proc->pid, threads, nodes, incoming_refs, outgoing_refs, active_transactions, buffers, page_count);
 
         kfree(proc);
+        if (files)
+                put_files_struct(files);
         return 0;
 }