coresight: ETR: Fix ETR buffer use-after-free issue

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: coresight: ETR: Fix ETR buffer use-after-free issue When ETR is enabled as CS_MODE_SYSFS, if the buffer size is changed and enabled again, currently sysfs_buf will point to the newly allocated memory(buf_new) and free the old memory(buf_old). But the etr_buf that is being used by the ETR remains pointed to buf_old, not updated to buf_new. In this case, it will result in a memory use-after-free issue. Fix this by checking ETR's mode before updating and releasing buf_old, if the mode is CS_MODE_SYSFS, then skip updating and releasing it.

References

• https://git.kernel.org/stable/c/70acbc9c77686b7a521af6d7a543dcd9c324cf07
• https://git.kernel.org/stable/c/cda077a19f5c8d6ec61e5b97deca203d95e3a422
• https://git.kernel.org/stable/c/35501ac3c7d40a7bb9568c2f89d6b56beaf9bed3