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efivarfs: Add uid/gid mount options 

Allow UEFI variables to be modified by non-root processes in order to
run sandboxed code. This doesn't change the behavior of mounting
efivarfs unless uid/gid are specified; by default both are set to root.

Signed-off-by: Jiao Zhou <jiaozhou@google.com>
Acked-by: Matthew Garrett <mgarrett@aurora.tech>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
This commit is contained in:
Jiao Zhou 2023-10-20 00:46:39 +02:00 committed by Ard Biesheuvel
parent 0bb80ecc33
commit 5329aa5101
3 changed files with 81 additions and 0 deletions
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4
fs/efivarfs/inode.c
View File

@ -21,8 +21,12 @@ struct inode *efivarfs_get_inode(struct super_block *sb,
dev_t dev, bool is_removable)
{
struct inode *inode = new_inode(sb);
struct efivarfs_fs_info *fsi = sb->s_fs_info;
struct efivarfs_mount_opts *opts = &fsi->mount_opts;
if (inode) {
inode->i_uid = opts->uid;
inode->i_gid = opts->gid;
inode->i_ino = get_next_ino();
inode->i_mode = mode;
inode->i_atime = inode->i_mtime = inode_set_ctime_current(inode);

9
fs/efivarfs/internal.h
View File

@ -9,6 +9,15 @@
#include <linux/list.h>
#include <linux/efi.h>
struct efivarfs_mount_opts {
kuid_t uid;
kgid_t gid;
};
struct efivarfs_fs_info {
struct efivarfs_mount_opts mount_opts;
};
struct efi_variable {
efi_char16_t VariableName[EFI_VAR_NAME_LEN/sizeof(efi_char16_t)];
efi_guid_t VendorGuid;

68
fs/efivarfs/super.c
View File

@ -8,6 +8,7 @@
#include <linux/efi.h>
#include <linux/fs.h>
#include <linux/fs_context.h>
#include <linux/fs_parser.h>
#include <linux/module.h>
#include <linux/pagemap.h>
#include <linux/ucs2_string.h>
@ -24,6 +25,21 @@ static void efivarfs_evict_inode(struct inode *inode)
clear_inode(inode);
}
static int efivarfs_show_options(struct seq_file *m, struct dentry *root)
{
struct super_block *sb = root->d_sb;
struct efivarfs_fs_info *sbi = sb->s_fs_info;
struct efivarfs_mount_opts *opts = &sbi->mount_opts;
if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
seq_printf(m, ",uid=%u",
from_kuid_munged(&init_user_ns, opts->uid));
if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
seq_printf(m, ",gid=%u",
from_kgid_munged(&init_user_ns, opts->gid));
return 0;
}
static int efivarfs_statfs(struct dentry *dentry, struct kstatfs *buf)
{
const u32 attr = EFI_VARIABLE_NON_VOLATILE |
@ -64,6 +80,7 @@ static const struct super_operations efivarfs_ops = {
.statfs = efivarfs_statfs,
.drop_inode = generic_delete_inode,
.evict_inode = efivarfs_evict_inode,
.show_options = efivarfs_show_options,
};
/*
@ -225,6 +242,45 @@ static int efivarfs_destroy(struct efivar_entry *entry, void *data)
return 0;
}
enum {
Opt_uid, Opt_gid,
};
static const struct fs_parameter_spec efivarfs_parameters[] = {
fsparam_u32("uid", Opt_uid),
fsparam_u32("gid", Opt_gid),
{},
};
static int efivarfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
struct efivarfs_fs_info *sbi = fc->s_fs_info;
struct efivarfs_mount_opts *opts = &sbi->mount_opts;
struct fs_parse_result result;
int opt;
opt = fs_parse(fc, efivarfs_parameters, param, &result);
if (opt < 0)
return opt;
switch (opt) {
case Opt_uid:
opts->uid = make_kuid(current_user_ns(), result.uint_32);
if (!uid_valid(opts->uid))
return -EINVAL;
break;
case Opt_gid:
opts->gid = make_kgid(current_user_ns(), result.uint_32);
if (!gid_valid(opts->gid))
return -EINVAL;
break;
default:
return -EINVAL;
}
return 0;
}
static int efivarfs_fill_super(struct super_block *sb, struct fs_context *fc)
{
struct inode *inode = NULL;
@ -271,10 +327,21 @@ static int efivarfs_get_tree(struct fs_context *fc)
static const struct fs_context_operations efivarfs_context_ops = {
.get_tree = efivarfs_get_tree,
.parse_param = efivarfs_parse_param,
};
static int efivarfs_init_fs_context(struct fs_context *fc)
{
struct efivarfs_fs_info *sfi;
sfi = kzalloc(sizeof(*sfi), GFP_KERNEL);
if (!sfi)
return -ENOMEM;
sfi->mount_opts.uid = GLOBAL_ROOT_UID;
sfi->mount_opts.gid = GLOBAL_ROOT_GID;
fc->s_fs_info = sfi;
fc->ops = &efivarfs_context_ops;
return 0;
}
@ -295,6 +362,7 @@ static struct file_system_type efivarfs_type = {
.name = "efivarfs",
.init_fs_context = efivarfs_init_fs_context,
.kill_sb = efivarfs_kill_sb,
.parameters = efivarfs_parameters,
};
static __init int efivarfs_init(void)