dasharo/linux
0
0
Fork 0
mirror of https://github.com/Dasharo/linux.git synced 2026-03-06 15:25:10 -08:00
Code Issues Packages Projects Releases Wiki Activity

efivarfs: fix NULL dereference on resume

Browse Source 
LSMs often inspect the path.mnt of files in the security hooks, and this
causes a NULL deref in efivarfs_pm_notify() because the path is
constructed with a NULL path.mnt.

Fix by obtaining from vfs_kern_mount() instead, and being very careful
to ensure that deactivate_super() (potentially triggered by a racing
userspace umount) is not called directly from the notifier, because it
would deadlock when efivarfs_kill_sb() tried to unregister the notifier
chain.

[ Al notes:
	Umm...  That's probably safe, but not as a long-term solution -
	it's too intimately dependent upon fs/super.c internals. The
	reasons why you can't run into ->s_umount deadlock here are
	non-trivial... ]

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Link: https://lore.kernel.org/r/e54e6a2f-1178-4980-b771-4d9bafc2aa47@tnxip.de
Link: https://lore.kernel.org/r/3e998bf87638a442cbc6864cdcd3d8d9e08ce3e3.camel@HansenPartnership.com
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
This commit is contained in:
James Bottomley
2025-03-17 23:06:01 -04:00
committed by Ard Biesheuvel
parent dec1277875
commit 11092db5b5
1 changed files with 48 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

50
fs/efivarfs/super.c
View File

@@ -474,12 +474,25 @@ static int efivarfs_check_missing(efi_char16_t *name16, efi_guid_t vendor,
return err;
}
static void efivarfs_deactivate_super_work(struct work_struct *work)
{
struct super_block *s = container_of(work, struct super_block,
destroy_work);
/*
* note: here s->destroy_work is free for reuse (which
* will happen in deactivate_super)
*/
deactivate_super(s);
}
static struct file_system_type efivarfs_type;
static int efivarfs_pm_notify(struct notifier_block *nb, unsigned long action,
void *ptr)
{
struct efivarfs_fs_info *sfi = container_of(nb, struct efivarfs_fs_info,
pm_nb);
struct path path = { .mnt = NULL, .dentry = sfi->sb->s_root, };
struct path path;
struct efivarfs_ctx ectx = {
.ctx = {
.actor = efivarfs_actor,
@@ -487,6 +500,7 @@ static int efivarfs_pm_notify(struct notifier_block *nb, unsigned long action,
.sb = sfi->sb,
};
struct file *file;
struct super_block *s = sfi->sb;
static bool rescan_done = true;
if (action == PM_HIBERNATION_PREPARE) {
@@ -499,11 +513,43 @@ static int efivarfs_pm_notify(struct notifier_block *nb, unsigned long action,
if (rescan_done)
return NOTIFY_DONE;
/* ensure single superblock is alive and pin it */
if (!atomic_inc_not_zero(&s->s_active))
return NOTIFY_DONE;
pr_info("efivarfs: resyncing variable state\n");
/* O_NOATIME is required to prevent oops on NULL mnt */
path.dentry = sfi->sb->s_root;
/*
* do not add SB_KERNMOUNT which a single superblock could
* expose to userspace and which also causes MNT_INTERNAL, see
* below
*/
path.mnt = vfs_kern_mount(&efivarfs_type, 0,
efivarfs_type.name, NULL);
if (IS_ERR(path.mnt)) {
pr_err("efivarfs: internal mount failed\n");
/*
* We may be the last pinner of the superblock but
* calling efivarfs_kill_sb from within the notifier
* here would deadlock trying to unregister it
*/
INIT_WORK(&s->destroy_work, efivarfs_deactivate_super_work);
schedule_work(&s->destroy_work);
return PTR_ERR(path.mnt);
}
/* path.mnt now has pin on superblock, so this must be above one */
atomic_dec(&s->s_active);
file = kernel_file_open(&path, O_RDONLY | O_DIRECTORY | O_NOATIME,
current_cred());
/*
* safe even if last put because no MNT_INTERNAL means this
* will do delayed deactivate_super and not deadlock
*/
mntput(path.mnt);
if (IS_ERR(file))
return NOTIFY_DONE;