misc: fastrpc: avoid double fput() on failed usercopy

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: misc: fastrpc: avoid double fput() on failed usercopy If the copy back to userland fails for the FASTRPC_IOCTL_ALLOC_DMA_BUFF ioctl(), we shouldn't assume that 'buf->dmabuf' is still valid. In fact, dma_buf_fd() called fd_install() before, i.e. "consumed" one reference, leaving us with none. Calling dma_buf_put() will therefore put a reference we no longer own, leading to a valid file descritor table entry for an already released 'file' object which is a straight use-after-free. Simply avoid calling dma_buf_put() and rely on the process exit code to do the necessary cleanup, if needed, i.e. if the file descriptor is still valid.

References

• https://git.kernel.org/stable/c/4e6fd2b5fcf8e7119305a6042bd92e7f2b9ed215
• https://git.kernel.org/stable/c/a5ce7ee5fcc07583159f54ab4af5164de00148f5
• https://git.kernel.org/stable/c/e4382d0a39f9a1e260d62fdc079ddae5293c037d
• https://git.kernel.org/stable/c/76f85c307ef9f10aa2cef1b1d5ee654c1f3345fc
• https://git.kernel.org/stable/c/46963e2e0629cb31c96b1d47ddd89dc3d8990b34