CVE-2025-39817

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

efivarfs: Fix slab-out-of-bounds in efivarfs_d_compare

Observed on kernel 6.6 (present on master as well):

BUG: KASAN: slab-out-of-bounds in memcmp+0x98/0xd0 Call trace: kasan_check_range+0xe8/0x190 __asan_loadN+0x1c/0x28 memcmp+0x98/0xd0 efivarfs_d_compare+0x68/0xd8 __d_lookup_rcu_op_compare+0x178/0x218 __d_lookup_rcu+0x1f8/0x228 d_alloc_parallel+0x150/0x648 lookup_open.isra.0+0x5f0/0x8d0 open_last_lookups+0x264/0x828 path_openat+0x130/0x3f8 do_filp_open+0x114/0x248 do_sys_openat2+0x340/0x3c0 __arm64_sys_openat+0x120/0x1a0

If dentry->d_name.len < EFI_VARIABLE_GUID_LEN , guid can become negative, leadings to oob. The issue can be triggered by parallel lookups using invalid filename:

T1 T2 lookup_open ->lookup simple_lookup d_add // invalid dentry is added to hash list

		lookup_open
		 d_alloc_parallel
		  __d_lookup_rcu
		   __d_lookup_rcu_op_compare
		    hlist_bl_for_each_entry_rcu
		    // invalid dentry can be retrieved
		     ->d_compare
		      efivarfs_d_compare
		      // oob

Fix it by checking guid before cmp.

Affected Software

References

• https://git.kernel.org/stable/c/0f63fbabeaaaaaaf5b742a2f4c1b4590d50bf1f6
• https://git.kernel.org/stable/c/568e7761279b99c6daa3002290fd6d8047ddb6d2
• https://git.kernel.org/stable/c/71581a82f38e5a4d807d71fc1bb59aead80ccf95
• https://git.kernel.org/stable/c/794399019301944fd6d2e0d7a51b3327e26c410e
• https://git.kernel.org/stable/c/925599eba46045930b850a98ae594d2e3028ac40
• https://git.kernel.org/stable/c/a6358f8cf64850f3f27857b8ed8c1b08cfc4685c
• https://git.kernel.org/stable/c/c2925cd6207079c3f4d040d082515db78d63afbf
• https://git.kernel.org/stable/c/d7f5e35e70507d10cbaff5f9e194ed54c4ee14f7