fbcon: fix integer overflow in fbcon_do_set_font

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: fbcon: fix integer overflow in fbcon_do_set_font Fix integer overflow vulnerabilities in fbcon_do_set_font() where font size calculations could overflow when handling user-controlled font parameters. The vulnerabilities occur when: 1. CALC_FONTSZ(h, pitch, charcount) performs h * pith * charcount multiplication with user-controlled values that can overflow. 2. FONT_EXTRA_WORDS * sizeof(int) + size addition can also overflow 3. This results in smaller allocations than expected, leading to buffer overflows during font data copying. Add explicit overflow checking using check_mul_overflow() and check_add_overflow() kernel helpers to safety validate all size calculations before allocation.

References

• https://git.kernel.org/stable/c/994bdc2d23c79087fbf7dcd9544454e8ebcef877
• https://git.kernel.org/stable/c/9c8ec14075c5317edd6b242f1be8167aa1e4e333
• https://git.kernel.org/stable/c/b8a6e85328aeb9881531dbe89bcd2637a06c3c95
• https://git.kernel.org/stable/c/a6eb9f423b3db000aaedf83367b8539f6b72dcfc
• https://git.kernel.org/stable/c/adac90bb1aaf45ca66f9db8ac100be16750ace78
• https://git.kernel.org/stable/c/4a4bac869560f943edbe3c2b032062f6673b13d3
• https://git.kernel.org/stable/c/c0c01f9aa08c8e10e10e8c9ebb5be01a4eff6eb7
• https://git.kernel.org/stable/c/1a194e6c8e1ee745e914b0b7f50fa86c89ed13fe