[PATCH 6.1] efivars: Fix "BUG: corrupted list in efivar_entry_remove"

[Alexey Nepomnyashih]

Prevent list corruption in efivar_entry_remove() and efivar_entry_list_del_unlock() 
by verifying that an entry is still in the list (list_empty() == false) before calling 
list_del(). Also reset the list pointers with INIT_LIST_HEAD() to avoid potential double-removal issues. 
Ensure robust handling of entries and prevent the kernel BUG observed when list_del() was called on an 
already-removed entry.
Fix https://syzkaller.appspot.com/bug?extid=246ea4feed277471958a

Syzkaller report:
list_del corruption. prev->next should be ffff0000d86d6828, but was ffff800016216e60. (prev=ffff800016216e60)
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:61!
Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 4299 Comm: syz-executor237 Not tainted 6.1.119-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : __list_del_entry_valid+0x13c/0x158 lib/list_debug.c:59
lr : __list_del_entry_valid+0x13c/0x158 lib/list_debug.c:59
Call trace:
 __list_del_entry_valid+0x13c/0x158 lib/list_debug.c:59
 __list_del_entry include/linux/list.h:134 [inline]
 list_del include/linux/list.h:148 [inline]
 efivar_entry_remove+0x38/0x110 fs/efivarfs/vars.c:493
 efivarfs_destroy+0x20/0x3c fs/efivarfs/super.c:184
 efivar_entry_iter+0x94/0xdc fs/efivarfs/vars.c:720
 efivarfs_kill_sb+0x58/0x70 fs/efivarfs/super.c:258
 deactivate_locked_super+0xac/0x124 fs/super.c:332
 deactivate_super+0xf0/0x110 fs/super.c:363
 cleanup_mnt+0x394/0x41c fs/namespace.c:1186
 __cleanup_mnt+0x20/0x30 fs/namespace.c:1193
 task_work_run+0x240/0x2f0 kernel/task_work.c:203
 resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
 do_notify_resume+0x2080/0x2cb8 arch/arm64/kernel/signal.c:1132
 prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
 exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
 el0_svc+0x9c/0x168 arch/arm64/kernel/entry-common.c:638
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

Reported-by: syzbot+75dc11...@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 2d82e6227ea1 ("efi: vars: Move efivar caching layer into efivarfs")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Alexey Nepomnyashih <sdl@xxxxxxxx>
---
 fs/efivarfs/vars.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/efivarfs/vars.c b/fs/efivarfs/vars.c
index 13bc60698955..42977138e30b 100644
--- a/fs/efivarfs/vars.c
+++ b/fs/efivarfs/vars.c
@@ -490,7 +490,10 @@ void __efivar_entry_add(struct efivar_entry *entry, struct list_head *head)
  */
 void efivar_entry_remove(struct efivar_entry *entry)
 {
-	list_del(&entry->list);
+	if (!list_empty(&entry->list)) {
+        list_del(&entry->list);
+        INIT_LIST_HEAD(&entry->list);
+	}
 }
 
 /*
@@ -506,7 +509,10 @@ void efivar_entry_remove(struct efivar_entry *entry)
  */
 static void efivar_entry_list_del_unlock(struct efivar_entry *entry)
 {
-	list_del(&entry->list);
+	if (!list_empty(&entry->list)) {
+        list_del(&entry->list);
+        INIT_LIST_HEAD(&entry->list);
+    }
 	efivar_unlock();
 }
 
-- 
2.43.0