drm/exynos: exynos7_drm_decon: add vblank check in IRQ handling

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: drm/exynos: exynos7_drm_decon: add vblank check in IRQ handling If there's support for another console device (such as a TTY serial), the kernel occasionally panics during boot. The panic message and a relevant snippet of the call stack is as follows: Unable to handle kernel NULL pointer dereference at virtual address 000000000000000 Call trace: drm_crtc_handle_vblank+0x10/0x30 (P) decon_irq_handler+0x88/0xb4 [...] Otherwise, the panics don't happen. This indicates that it's some sort of race condition. Add a check to validate if the drm device can handle vblanks before calling drm_crtc_handle_vblank() to avoid this.

References

• https://git.kernel.org/stable/c/b4e72c0bf878f02faa00a7dc7c9ffc4ff7c116a7
• https://git.kernel.org/stable/c/a2130463fc9451005660b0eda7b61d5f746f7d74
• https://git.kernel.org/stable/c/87825fbd1e176cd5b896940f3959e7c9a916945d
• https://git.kernel.org/stable/c/a40a35166f7e4f6dcd4b087d620c8228922dcb0a
• https://git.kernel.org/stable/c/391e5ea5b877230b844c9bd8bbcd91b681b1ce2d
• https://git.kernel.org/stable/c/e9d9b25f376737b81f06de9c5aa422b488f47184
• https://git.kernel.org/stable/c/996740652e620ef8ee1e5c65832cf2ffa498577d
• https://git.kernel.org/stable/c/b846350aa272de99bf6fecfa6b08e64ebfb13173