media: av7110: prevent underflow in write_ts_to_decoder()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: media: av7110: prevent underflow in write_ts_to_decoder() The buf[4] value comes from the user via ts_play(). It is a value in the u8 range. The final length we pass to av7110_ipack_instant_repack() is "len - (buf[4] + 1) - 4" so add a check to ensure that the length is not negative. It's not clear that passing a negative len value does anything bad necessarily, but it's not best practice. With the new bounds checking the "if (!len)" condition is no longer possible or required so remove that.

References

• https://git.kernel.org/stable/c/6680af5be9f08d830567e9118f76d3e64684db8f
• https://git.kernel.org/stable/c/6606e2404ee9e20a3ae5b42fc3660d41b739ed3e
• https://git.kernel.org/stable/c/620b983589e0223876bf1463b01100a9c67b56ba
• https://git.kernel.org/stable/c/86ba65e5357bfbb6c082f68b265a292ee1bdde1d
• https://git.kernel.org/stable/c/ca4ce92e3ec9fd3c7c936b912b95c53331d5159c
• https://git.kernel.org/stable/c/423350af9e27f005611bd881b1df2cab66de943d
• https://git.kernel.org/stable/c/77eeb4732135c18c2fdfab80839645b393f3e774
• https://git.kernel.org/stable/c/7b93ab60fe9ed04be0ff155bc30ad39dea23e22b
• https://git.kernel.org/stable/c/eed9496a0501357aa326ddd6b71408189ed872eb