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efi: vars: prohibit reading random seed variables

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In anticipation of putting random seeds in EFI variables, it's important
that the random GUID namespace of variables remains hidden from
userspace. We accomplish this by not populating efivarfs with entries
from that GUID, as well as denying the creation of new ones in that
GUID.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
This commit is contained in:
Jason A. Donenfeld 2022-11-22 03:04:00 +01:00 committed by Ard Biesheuvel
parent 196dff2712
commit 63ffb573df
2 changed files with 7 additions and 0 deletions
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4
fs/efivarfs/inode.c
View file

@ -91,6 +91,10 @@ static int efivarfs_create(struct user_namespace *mnt_userns, struct inode *dir,
err = guid_parse(dentry->d_name.name + namelen + 1, &var->var.VendorGuid);
if (err)
goto out;
if (guid_equal(&var->var.VendorGuid, &LINUX_EFI_RANDOM_SEED_TABLE_GUID)) {
err = -EPERM;
goto out;
}
if (efivar_variable_is_removable(var->var.VendorGuid,
dentry->d_name.name, namelen))

3
fs/efivarfs/super.c
View file

@ -116,6 +116,9 @@ static int efivarfs_callback(efi_char16_t *name16, efi_guid_t vendor,
int err = -ENOMEM;
bool is_removable = false;
if (guid_equal(&vendor, &LINUX_EFI_RANDOM_SEED_TABLE_GUID))
return 0;
entry = kzalloc(sizeof(*entry), GFP_KERNEL);
if (!entry)
return err;