CVE-2025-38207 Information

Jul 05, 2025 cve

Description

In the Linux kernel the following vulnerability has been resolved:

mm: fix uprobe pte be overwritten when expanding vma

Patch series \Fix uprobe pte be overwritten when expanding vma.

This patch (of 4):

We encountered a BUG alert triggered by Syzkaller as follows: BUG: Bad rss-counter state mm:00000000b4a60fca type:MM_ANONPAGES val:1

And we can reproduce it with the following steps:

  1. register uprobe on file at zero offset
  2. mmap the file at zero offset: addr1 = mmap(NULL 2 4096 PROT_NONE MAP_PRIVATE fd 0);
  3. mremap part of vma1 to new vma2: addr2 = mremap(addr1 4096 2 4096 MREMAP_MAYMOVE);
  4. mremap back to orig addr1: mremap(addr2 4096 4096 MREMAP_MAYMOVE | MREMAP_FIXED addr1);

In step 3 the vma1 range [addr1 addr1 + 4096] will be remap to new vma2 with range [addr2 addr2 + 8192] and remap uprobe anon page from the vma1 to vma2 then unmap the vma1 range [addr1 addr1 + 4096].

In step 4 the vma2 range [addr2 addr2 + 4096] will be remap back to the addr range [addr1 addr1 + 4096]. Since the addr range [addr1 + 4096 addr1 + 8192] still maps the file it will take vma_merge_new_range to expand the range and then do uprobe_mmap in vma_complete. Since the merged vma pgoff is also zero offset it will install uprobe anon page to the merged vma. However the upcomming move_page_tables step which use set_pte_at to remap the vma2 uprobe pte to the merged vma will overwrite the newly uprobe pte in the merged vma and lead that pte to be orphan.

Since the uprobe pte will be remapped to the merged vma we can remove the unnecessary uprobe_mmap upon merged vma.

This problem was first found in linux-6.6.y and also exists in the community syzkaller: https://lore.kernel.org/all/000000000000ada39605a5e71711@google.com/T/

Reference

https://git.kernel.org/stable/c/2b12d06c37fd3a394376f42f026a7478d826ed63 https://git.kernel.org/stable/c/58b83b9a9a929611a2a2e7d88f45cb0d786b7ee0

CNNVD-202507-474 (Published: 2025-07-04)

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