On 21/06/2020 13:30, Tuomas Tynkkynen wrote:
> Syzbot reports a NULL-ptr deref in the kref_put() call:
>
> BUG: KASAN: null-ptr-deref in media_request_put
> drivers/media/mc/mc-request.c:81 [inline]
> kref_put include/linux/kref.h:64 [inline]
> media_request_put drivers/media/mc/mc-request.c:81 [inline]
> media_request_close+0x4d/0x170 drivers/media/mc/mc-request.c:89
> __fput+0x2ed/0x750 fs/file_table.c:281
> task_work_run+0x147/0x1d0 kernel/task_work.c:123
> tracehook_notify_resume include/linux/tracehook.h:188 [inline]
> exit_to_usermode_loop arch/x86/entry/common.c:165 [inline]
> prepare_exit_to_usermode+0x48e/0x600 arch/x86/entry/common.c:196
>
> What led to this crash was an injected memory allocation failure in
> media_request_alloc():
>
> FAULT_INJECTION: forcing a failure.
> name failslab, interval 1, probability 0, space 0, times 0
> should_failslab+0x5/0x20
> kmem_cache_alloc_trace+0x57/0x300
> ? anon_inode_getfile+0xe5/0x170
> media_request_alloc+0x339/0x440
> media_device_request_alloc+0x94/0xc0
> media_device_ioctl+0x1fb/0x330
> ? do_vfs_ioctl+0x6ea/0x1a00
> ? media_ioctl+0x101/0x120
> ? __media_device_usb_init+0x430/0x430
> ? media_poll+0x110/0x110
> __se_sys_ioctl+0xf9/0x160
> do_syscall_64+0xf3/0x1b0
>
> When that allocation fails, filp->private_data is left uninitialized
> which media_request_close() does not expect and crashes.
>
> To avoid this, reorder media_request_alloc() such that
> allocating the struct file happens as the last step thus
> media_request_close() will no longer get called for a partially created
> media request.
>
> Reported-by: syzbot+6bed2d543cf7e48b8...@syzkaller.appspotmail.com
> Cc: sta...@vger.kernel.org
> Signed-off-by: Tuomas Tynkkynen <tuomas.tynkky...@iki.fi>
Reviewed-by: Hans Verkuil <hverkuil-ci...@xs4all.nl>
Thanks!
Hans
> ---
> drivers/media/mc/mc-request.c | 31 +++++++++++++++++--------------
> 1 file changed, 17 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/media/mc/mc-request.c b/drivers/media/mc/mc-request.c
> index e3fca436c75b..c0782fd96c59 100644
> --- a/drivers/media/mc/mc-request.c
> +++ b/drivers/media/mc/mc-request.c
> @@ -296,9 +296,18 @@ int media_request_alloc(struct media_device *mdev, int
> *alloc_fd)
> if (WARN_ON(!mdev->ops->req_alloc ^ !mdev->ops->req_free))
> return -ENOMEM;
>
> + if (mdev->ops->req_alloc)
> + req = mdev->ops->req_alloc(mdev);
> + else
> + req = kzalloc(sizeof(*req), GFP_KERNEL);
> + if (!req)
> + return -ENOMEM;
> +
> fd = get_unused_fd_flags(O_CLOEXEC);
> - if (fd < 0)
> - return fd;
> + if (fd < 0) {
> + ret = fd;
> + goto err_free_req;
> + }
>
> filp = anon_inode_getfile("request", &request_fops, NULL, O_CLOEXEC);
> if (IS_ERR(filp)) {
> @@ -306,15 +315,6 @@ int media_request_alloc(struct media_device *mdev, int
> *alloc_fd)
> goto err_put_fd;
> }
>
> - if (mdev->ops->req_alloc)
> - req = mdev->ops->req_alloc(mdev);
> - else
> - req = kzalloc(sizeof(*req), GFP_KERNEL);
> - if (!req) {
> - ret = -ENOMEM;
> - goto err_fput;
> - }
> -
> filp->private_data = req;
> req->mdev = mdev;
> req->state = MEDIA_REQUEST_STATE_IDLE;
> @@ -336,12 +336,15 @@ int media_request_alloc(struct media_device *mdev, int
> *alloc_fd)
>
> return 0;
>
> -err_fput:
> - fput(filp);
> -
> err_put_fd:
> put_unused_fd(fd);
>
> +err_free_req:
> + if (mdev->ops->req_free)
> + mdev->ops->req_free(req);
> + else
> + kfree(req);
> +
> return ret;
> }
>
>
