CVE-2025-21933: linux kernel Null Dereference — Fix

Description

In the Linux kernel, the following vulnerability has been resolved: arm: pgtable: fix NULL pointer dereference issue When update_mmu_cache_range() is called by update_mmu_cache(), the vmf parameter is NULL, which will cause a NULL pointer dereference issue in adjust_pte(): Unable to handle kernel NULL pointer dereference at virtual address 00000030 when read Hardware name: Atmel AT91SAM9 PC is at update_mmu_cache_range+0x1e0/0x278 LR is at pte_offset_map_rw_nolock+0x18/0x2c Call trace: update_mmu_cache_range from remove_migration_pte+0x29c/0x2ec remove_migration_pte from rmap_walk_file+0xcc/0x130 rmap_walk_file from remove_migration_ptes+0x90/0xa4 remove_migration_ptes from migrate_pages_batch+0x6d4/0x858 migrate_pages_batch from migrate_pages+0x188/0x488 migrate_pages from compact_zone+0x56c/0x954 compact_zone from compact_node+0x90/0xf0 compact_node from kcompactd+0x1d4/0x204 kcompactd from kthread+0x120/0x12c kthread from ret_from_fork+0x14/0x38 Exception stack(0xc0d8bfb0 to 0xc0d8bff8) To fix it, do not rely on whether 'ptl' is equal to decide whether to hold the pte lock, but decide it by whether CONFIG_SPLIT_PTE_PTLOCKS is enabled. In addition, if two vmas map to the same PTE page, there is no need to hold the pte lock again, otherwise a deadlock will occur. Just add the need_lock parameter to let adjust_pte() know this information.

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CVSS v3.1 Score

5.5

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-476 CWE-476

Affected Products

Vendor	Product	Versions
linux	linux_kernel	6.13 — 6.13.7
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/91d011efe30aedde067ce6d218d521cf99b162e5 https://git.kernel.org/stable/c/a564ccfe300fa6a065beda06ab7f3c140d6b4d63

Frequently Asked Questions

What is CVE-2025-21933? +

In the Linux kernel, the following vulnerability has been resolved: arm: pgtable: fix NULL pointer dereference issue When update_mmu_cache_range() is called by update_mmu_cache(), the vmf parameter is NULL, which will cause a NULL pointer dereference issue in adjust_pte(): Unable to handle kernel NULL pointer dereference at virtual address 00000030 when read Hardware name: Atmel AT91SAM9 PC is at update_mmu_cache_range+0x1e0/0x278 LR is at pte_offset_map_rw_nolock+0x18/0x2c Call trace: update_mmu_cache_range from remove_migration_pte+0x29c/0x2ec remove_migration_pte from rmap_walk_file+0xcc/0x130 rmap_walk_file from remove_migration_ptes+0x90/0xa4 remove_migration_ptes from migrate_pages_batch+0x6d4/0x858 migrate_pages_batch from migrate_pages+0x188/0x488 migrate_pages from compact_zone+0x56c/0x954 compact_zone from compact_node+0x90/0xf0 compact_node from kcompactd+0x1d4/0x204 kcompactd from kthread+0x120/0x12c kthread from ret_from_fork+0x14/0x38 Exception stack(0xc0d8bfb0 to 0xc0d8bff8) To fix it, do not rely on whether 'ptl' is equal to decide whether to hold the pte lock, but decide it by whether CONFIG_SPLIT_PTE_PTLOCKS is enabled. In addition, if two vmas map to the same PTE page, there is no need to hold the pte lock again, otherwise a deadlock will occur. Just add the need_lock parameter to let adjust_pte() know this information. It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2025-21933? +

CVE-2025-21933 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2025-21933? +

CVE-2025-21933 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-21933? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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