CVE-2026-46209

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

drm/gem: Fix inconsistent plane dimension calculation in drmgemfbinitwith_funcs()

drmgemfbinitwith_funcs() computes sub-sampled plane dimensions using plain integer division:

unsigned int width = modecmd->width / (i ? info->hsub : 1); unsigned int height = modecmd->height / (i ? info->vsub : 1);

However, the ioctl-level framebuffercheck() in drmframebuffer.c uses drmformatinfoplanewidth/height() which round up dimensions via DIVROUNDUP(). This inconsistency corrupts the subsequent GEM object size check for certain pixel format and dimension combinations.

For example, with NV12 (vsub=2) and a 1-pixel-tall framebuffer the GEM size validation path sees height=0 instead of height=1. The expression (height - 1) then wraps to UINTMAX as an unsigned int, causing minsize to overflow and wrap back to a small value. A tiny GEM object therefore passes the size guard, yet when the GPU accesses the chroma plane it will read or write memory beyond the object's bounds.

Fix by replacing the open-coded divisions with drmformatinfoplanewidth() and drmformatinfoplaneheight(), which use DIVROUNDUP() and match the calculation already used in framebuffer_check().