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>

diff --git a/fs/efivarfs/inode.c b/fs/efivarfs/inode.c
index db9231f0e77b60f860e96de10308c8077b9fda51..92e5e060e0eecb0191cfd5f9e98fb3b4152f0094 100644 (file)
--- a/fs/efivarfs/inode.c
+++ b/fs/efivarfs/inode.c
@@ -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);

diff --git a/fs/efivarfs/internal.h b/fs/efivarfs/internal.h
index 8ebf3a6a8aa2d620e5960530378ca8fd6ad84e34..c66647f5c0bdb72a36c98cac5db7d4887e0a87d1 100644 (file)
--- a/fs/efivarfs/internal.h
+++ b/fs/efivarfs/internal.h
@@ -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;

diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
index e028fafa04f38c51739bb56c796bb5d854c7c4ba..46c6446ec28045c73f06d3bdac1b323a477bf96c 100644 (file)
--- a/fs/efivarfs/super.c
+++ b/fs/efivarfs/super.c
@@ -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)