Use After Free Affecting linux-qemu-melange package, versions <6.18.49-r2

Note: Versions mentioned in the description apply only to the upstream linux-qemu-melange package and not the linux-qemu-melange package as distributed by Chainguard. See How to fix? for Chainguard relevant fixed versions and status.

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

fbdev: omap2: fix use-after-free in omapfb_mmap

omapfb_mmap() has a race condition with OMAPFB_SETUP_PLANE ioctl that can lead to use-after-free:

The fb_mmap() entry point holds mm_lock but not lock (fb_info->lock), while ioctl handlers like OMAPFB_SETUP_PLANE hold lock but not mm_lock. This allows concurrent execution.

In omapfb_mmap():

1. rg = omapfb_get_mem_region(ofbi->region); // Get old region ref
2. start = omapfb_get_region_paddr(ofbi); // Read from NEW region
3. len = fix->smem_len; // Read from NEW region
4. vm_iomap_memory(vma, start, len); // Map NEW region memory
5. atomic_inc(&rg->map_count); // Increment OLD region!

Concurrently, OMAPFB_SETUP_PLANE can:

• Reassign ofbi->region = new_rg
• Update fix->smem_len
• OMAPFB_SETUP_MEM then checks NEW region's map_count (0!) and frees it

This leaves userspace with a mapping to freed physical memory.

The fix is to read all required values (start, len) from the same region reference (rg) that will have its map_count incremented, preventing the region from being freed while still mapped.

• https://git.kernel.org/stable/c/6eb6ebcc8590007ad59ddccc8b5f9201655b33f8
• https://git.kernel.org/stable/c/7958e67375aa111522086286bba13cfc0816ce8d
• https://git.kernel.org/stable/c/8363c219d88e78daaee5665117a0380442989338