drm/buddy: Prevent BUG_ON by validating rounded allocation

Overview

In the Linux kernel, the following vulnerability has been resolved:

drm/buddy: Prevent BUG_ON by validating rounded allocation

When DRM_BUDDY_CONTIGUOUS_ALLOCATION is set, the requested size is rounded up to the next power-of-two via roundup_pow_of_two(). Similarly, for non-contiguous allocations with large min_block_size, the size is aligned up via round_up(). Both operations can produce a rounded size that exceeds mm->size, which later triggers BUG_ON(order > mm->max_order).

Example scenarios:

• 9G CONTIGUOUS allocation on 10G VRAM memory: roundup_pow_of_two(9G) = 16G > 10G
• 9G allocation with 8G min_block_size on 10G VRAM memory: round_up(9G, 8G) = 16G > 10G

Fix this by checking the rounded size against mm->size. For non-contiguous or range allocations where size > mm->size is invalid, return -EINVAL immediately. For contiguous allocations without range restrictions, allow the request to fall through to the existing __alloc_contig_try_harder() fallback.

This ensures invalid user input returns an error or uses the fallback path instead of hitting BUG_ON.

v2: (Matt A)

• Add Fixes, Cc stable, and Closes tags for context

Affected

• Linux >= 0a1844bf0b532d84324453374ad6845f64066c28 < d764b8dd420098a4d253b8a5b27568c897edb2cf
• Linux >= 0a1844bf0b532d84324453374ad6845f64066c28 < 6236c1cd9fdf433d39ed28b2491ccdfe7ae95061
• Linux >= 0a1844bf0b532d84324453374ad6845f64066c28 < ecb32c60d8cbed2ee9ce9f343b6aa2f32babc727
• Linux >= 0a1844bf0b532d84324453374ad6845f64066c28 < 5488a29596cdba93a60a79398dc9b69d5bdadf92
• Linux 6.7

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.