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Message-ID: <20230907170146.1055954-1-jiaozhou@google.com>
Date: Thu, 7 Sep 2023 17:01:46 +0000
From: Jiao Zhou <jiaozhou@...gle.com>
To: Linux FS Development <linux-fsdevel@...r.kernel.org>
Cc: Jiao Zhou <jiaozhou@...gle.com>, Ard Biesheuvel <ardb@...nel.org>,
Jeremy Kerr <jk@...abs.org>, linux-efi@...r.kernel.org,
linux-kernel@...r.kernel.org, mjg59@...f.ucam.org,
Matthew Garrett <mgarrett@...ora.tech>
Subject: [PATCH v5] 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@...gle.com>
Acked-by: Matthew Garrett <mgarrett@...ora.tech>
---
Changelog since v1:
- Add missing sentinel entry in fs_parameter_spec[] array.
- Fix a NULL pointer dereference.
Changelog since v2:
- Format the patch description.
Changelog since v3:
- Add gid and uid check to make sure that ids are valid.
- Drop the indentation for one block.
- Use sizeof(*sfi) to allocate memory to avoids future problems if sfi ever changes type.
Changelog since v4:
- Fix the use of sizeof.
---
fs/efivarfs/inode.c | 4 +++
fs/efivarfs/internal.h | 9 +++++
fs/efivarfs/super.c | 74 ++++++++++++++++++++++++++++++++++++++++--
3 files changed, 84 insertions(+), 3 deletions(-)
diff --git a/fs/efivarfs/inode.c b/fs/efivarfs/inode.c
index db9231f0e77b..06dfc73fda04 100644
--- a/fs/efivarfs/inode.c
+++ b/fs/efivarfs/inode.c
@@ -20,9 +20,13 @@ struct inode *efivarfs_get_inode(struct super_block *sb,
const struct inode *dir, int mode,
dev_t dev, bool is_removable)
{
+ struct efivarfs_fs_info *fsi = sb->s_fs_info;
struct inode *inode = new_inode(sb);
+ 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 8ebf3a6a8aa2..c66647f5c0bd 100644
--- 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 e028fafa04f3..ba14736ebae0 100644
--- 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;
@@ -270,11 +326,22 @@ static int efivarfs_get_tree(struct fs_context *fc)
}
static const struct fs_context_operations efivarfs_context_ops = {
- .get_tree = efivarfs_get_tree,
+ .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;
}
@@ -291,10 +358,11 @@ static void efivarfs_kill_sb(struct super_block *sb)
}
static struct file_system_type efivarfs_type = {
- .owner = THIS_MODULE,
- .name = "efivarfs",
+ .owner = THIS_MODULE,
+ .name = "efivarfs",
.init_fs_context = efivarfs_init_fs_context,
.kill_sb = efivarfs_kill_sb,
+ .parameters = efivarfs_parameters,
};
static __init int efivarfs_init(void)
--
2.42.0.283.g2d96d420d3-goog
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