linux-kernel - [PATCH v3] efivarfs: Fix slab-out-of-bounds in efivarfs_d

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Message-Id: <20250827073954.2046464-1-linan666@huaweicloud.com>
Date: Wed, 27 Aug 2025 15:39:54 +0800
From: linan666@...weicloud.com
To: jk@...abs.org,
	ardb@...nel.org,
	matt.fleming@...el.com
Cc: linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linan666@...weicloud.com,
	yangerkun@...wei.com,
	yi.zhang@...wei.com
Subject: [PATCH v3] efivarfs: Fix slab-out-of-bounds in efivarfs_d_compare

From: Li Nan <linan122@...wei.com>

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.

Fixes: da27a24383b2 ("efivarfs: guid part of filenames are case-insensitive")
Signed-off-by: Li Nan <linan122@...wei.com>
Signed-off-by: Wu Guanghao <wuguanghao3@...wei.com>
---
v3: Check guid directly, add comment. Emphasize 'invalid filename' in
    commit message.

 fs/efivarfs/super.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
index c4a139911356..4bb4002e3cdf 100644
--- a/fs/efivarfs/super.c
+++ b/fs/efivarfs/super.c
@@ -152,6 +152,10 @@ static int efivarfs_d_compare(const struct dentry *dentry,
 {
 	int guid = len - EFI_VARIABLE_GUID_LEN;
 
+	/* Parallel lookups may produce a temporary invalid filename */
+	if (guid <= 0)
+		return 1;
+
 	if (name->len != len)
 		return 1;
 
-- 
2.39.2