CVE-2022-48821

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 shouldnt 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.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

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