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authorTodd Kjos <tkjos@android.com>2018-12-14 15:58:21 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-12-19 09:40:13 +0100
commit80cd795630d6526ba729a089a435bf74a57af927 (patch)
treebc1d2b779bf5e506c66f96ee2210101c17652b59 /drivers/android
parent2701e804f00f79823f69f37c87fef171ac345484 (diff)
downloadlinux-80cd795630d6526ba729a089a435bf74a57af927.tar.bz2
binder: fix use-after-free due to ksys_close() during fdget()
44d8047f1d8 ("binder: use standard functions to allocate fds") exposed a pre-existing issue in the binder driver. fdget() is used in ksys_ioctl() as a performance optimization. One of the rules associated with fdget() is that ksys_close() must not be called between the fdget() and the fdput(). There is a case where this requirement is not met in the binder driver which results in the reference count dropping to 0 when the device is still in use. This can result in use-after-free or other issues. If userpace has passed a file-descriptor for the binder driver using a BINDER_TYPE_FDA object, then kys_close() is called on it when handling a binder_ioctl(BC_FREE_BUFFER) command. This violates the assumptions for using fdget(). The problem is fixed by deferring the close using task_work_add(). A new variant of __close_fd() was created that returns a struct file with a reference. The fput() is deferred instead of using ksys_close(). Fixes: 44d8047f1d87a ("binder: use standard functions to allocate fds") Suggested-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Todd Kjos <tkjos@google.com> Cc: stable <stable@vger.kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/android')
-rw-r--r--drivers/android/binder.c63
1 files changed, 61 insertions, 2 deletions
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index d653e8a474fc..210940bd0457 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -72,6 +72,7 @@
#include <linux/spinlock.h>
#include <linux/ratelimit.h>
#include <linux/syscalls.h>
+#include <linux/task_work.h>
#include <uapi/linux/android/binder.h>
@@ -2170,6 +2171,64 @@ static bool binder_validate_fixup(struct binder_buffer *b,
return (fixup_offset >= last_min_offset);
}
+/**
+ * struct binder_task_work_cb - for deferred close
+ *
+ * @twork: callback_head for task work
+ * @fd: fd to close
+ *
+ * Structure to pass task work to be handled after
+ * returning from binder_ioctl() via task_work_add().
+ */
+struct binder_task_work_cb {
+ struct callback_head twork;
+ struct file *file;
+};
+
+/**
+ * binder_do_fd_close() - close list of file descriptors
+ * @twork: callback head for task work
+ *
+ * It is not safe to call ksys_close() during the binder_ioctl()
+ * function if there is a chance that binder's own file descriptor
+ * might be closed. This is to meet the requirements for using
+ * fdget() (see comments for __fget_light()). Therefore use
+ * task_work_add() to schedule the close operation once we have
+ * returned from binder_ioctl(). This function is a callback
+ * for that mechanism and does the actual ksys_close() on the
+ * given file descriptor.
+ */
+static void binder_do_fd_close(struct callback_head *twork)
+{
+ struct binder_task_work_cb *twcb = container_of(twork,
+ struct binder_task_work_cb, twork);
+
+ fput(twcb->file);
+ kfree(twcb);
+}
+
+/**
+ * binder_deferred_fd_close() - schedule a close for the given file-descriptor
+ * @fd: file-descriptor to close
+ *
+ * See comments in binder_do_fd_close(). This function is used to schedule
+ * a file-descriptor to be closed after returning from binder_ioctl().
+ */
+static void binder_deferred_fd_close(int fd)
+{
+ struct binder_task_work_cb *twcb;
+
+ twcb = kzalloc(sizeof(*twcb), GFP_KERNEL);
+ if (!twcb)
+ return;
+ init_task_work(&twcb->twork, binder_do_fd_close);
+ __close_fd_get_file(fd, &twcb->file);
+ if (twcb->file)
+ task_work_add(current, &twcb->twork, true);
+ else
+ kfree(twcb);
+}
+
static void binder_transaction_buffer_release(struct binder_proc *proc,
struct binder_buffer *buffer,
binder_size_t *failed_at)
@@ -2309,7 +2368,7 @@ static void binder_transaction_buffer_release(struct binder_proc *proc,
}
fd_array = (u32 *)(parent_buffer + (uintptr_t)fda->parent_offset);
for (fd_index = 0; fd_index < fda->num_fds; fd_index++)
- ksys_close(fd_array[fd_index]);
+ binder_deferred_fd_close(fd_array[fd_index]);
} break;
default:
pr_err("transaction release %d bad object type %x\n",
@@ -3928,7 +3987,7 @@ static int binder_apply_fd_fixups(struct binder_transaction *t)
} else if (ret) {
u32 *fdp = (u32 *)(t->buffer->data + fixup->offset);
- ksys_close(*fdp);
+ binder_deferred_fd_close(*fdp);
}
list_del(&fixup->fixup_entry);
kfree(fixup);