mxser: fix xmit_buf leak in activate when LSR == 0xff

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: mxser: fix xmit_buf leak in activate when LSR == 0xff When LSR is 0xff in ->activate() (rather unlike), we return an error. Provided ->shutdown() is not called when ->activate() fails, nothing actually frees the buffer in this case. Fix this by properly freeing the buffer in a designated label. We jump there also from the "!info->type" if now too.

References

• https://git.kernel.org/stable/c/376922045009f8ea2d20a8fa3475e95b47c41690
• https://git.kernel.org/stable/c/125b7c929fc9b1e5eaa344bceb6367dfa6fd3f9d
• https://git.kernel.org/stable/c/685b6d16bf89595310b5d61394c9b97cc9505c7c
• https://git.kernel.org/stable/c/996291d06851a26678a0fab488b6e1f0677c0576
• https://git.kernel.org/stable/c/2cd05c38a27bee7fb42aa4d43174d68ac55dac0f
• https://git.kernel.org/stable/c/b125b08dbee3611f03f53b71471813ed4ccafcdd
• https://git.kernel.org/stable/c/6c9041b2f90c0eace73106f22350e1d2c98f5edc
• https://git.kernel.org/stable/c/6dffc2035fbaada60ca8db59e0962e34f760370a
• https://git.kernel.org/stable/c/cd3a4907ee334b40d7aa880c7ab310b154fd5cd4