fbdev: Add bounds checking in bit_putcs to fix vmalloc-out-of-bounds

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: fbdev: Add bounds checking in bit_putcs to fix vmalloc-out-of-bounds Add bounds checking to prevent writes past framebuffer boundaries when rendering text near screen edges. Return early if the Y position is off-screen and clip image height to screen boundary. Break from the rendering loop if the X position is off-screen. When clipping image width to fit the screen, update the character count to match the clipped width to prevent buffer size mismatches. Without the character count update, bit_putcs_aligned and bit_putcs_unaligned receive mismatched parameters where the buffer is allocated for the clipped width but cnt reflects the original larger count, causing out-of-bounds writes.

References

• https://git.kernel.org/stable/c/996bfaa7372d6718b6d860bdf78f6618e850c702
• https://git.kernel.org/stable/c/f0982400648a3e00580253e0c48e991f34d2684c
• https://git.kernel.org/stable/c/1943b69e87b0ab35032d47de0a7fca9a3d1d6fc1
• https://git.kernel.org/stable/c/ebc0730b490c7f27340b1222e01dd106e820320d
• https://git.kernel.org/stable/c/86df8ade88d290725554cefd03101ecd0fbd3752
• https://git.kernel.org/stable/c/15ba9acafb0517f8359ca30002c189a68ddbb939
• https://git.kernel.org/stable/c/2d1359e11674ed4274934eac8a71877ae5ae7bbb
• https://git.kernel.org/stable/c/3637d34b35b287ab830e66048841ace404382b67