From 80cd795630d6526ba729a089a435bf74a57af927 Mon Sep 17 00:00:00 2001 From: Todd Kjos Date: Fri, 14 Dec 2018 15:58:21 -0800 Subject: 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 Signed-off-by: Todd Kjos Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 61 insertions(+), 2 deletions(-) (limited to 'drivers/android/binder.c') 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 #include #include +#include #include @@ -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); -- cgit v1.2.1