[PATCH 6.1 v2 1/2] efivarfs: Add uid/gid mount options

[PATCH 6.1 v2 1/2] efivarfs: Add uid/gid mount options

[Alexey Nepomnyashih]

From: Jiao Zhou <jiaozhou@google.com>

commit 5329aa5101f73c451bcd48deaf3f296685849d9c upstream.

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>
Signed-off-by: Alexey Nepomnyashih <sdl@nppct.ru>
---
 fs/efivarfs/inode.c    |  4 +++
 fs/efivarfs/internal.h |  9 ++++++
 fs/efivarfs/super.c    | 68 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 81 insertions(+)

diff --git a/fs/efivarfs/inode.c b/fs/efivarfs/inode.c
index b3dc7ff42400..e93f2afd6741 100644
--- 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->i_ctime = current_time(inode);
diff --git a/fs/efivarfs/internal.h b/fs/efivarfs/internal.h
index dcb973d8736c..0762c0a1d207 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 b8c4641ed152..b4f1c46ea06f 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>
@@ -24,10 +25,26 @@ 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 const struct super_operations efivarfs_ops = {
 	.statfs = simple_statfs,
 	.drop_inode = generic_delete_inode,
 	.evict_inode = efivarfs_evict_inode,
+	.show_options = efivarfs_show_options,
 };
 
 /*
@@ -183,6 +200,45 @@ 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;
@@ -236,11 +292,22 @@ static int efivarfs_reconfigure(struct fs_context *fc)
 
 static const struct fs_context_operations efivarfs_context_ops = {
 	.get_tree	= efivarfs_get_tree,
+	.parse_param	= efivarfs_parse_param,
 	.reconfigure	= efivarfs_reconfigure,
 };
 
 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;
 }
@@ -261,6 +328,7 @@ 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)
-- 
2.43.0

[PATCH 6.1 v2 2/2] efivarfs: Move efivarfs list into superblock s_fs_info

[Alexey Nepomnyashih]

From: Ard Biesheuvel <ardb@kernel.org>

commit cdb46a8aefbf7fd36772bb206aaaf7e45d7cf8f6 upstream.

syzbot reports issues with concurrent fsopen()/fsconfig() invocations on
efivarfs, which are the result of the fact that the efivarfs list (which
caches the names and GUIDs of existing EFI variables) is a global
structure. In normal use, these issues are unlikely to trigger, even in
the presence of multiple mounts of efivarfs, but the execution pattern
used by the syzkaller reproducer may result in multiple instances of the
superblock that share the global efivarfs list, and this causes list
corruption when the list is reinitialized by one user while another is
traversing it.

So let's move the list head into the superblock s_fs_info field, so that
it will never be shared between distinct instances of the superblock. In
the common case, there will still be a single instance of this list, but
in the artificial syzkaller case, no list corruption can occur any
longer.

Reported-by: syzbot+1902c359bfcaf39c46f2@syzkaller.appspotmail.com
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reported-by: syzbot+246ea4feed277471958a@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=246ea4feed277471958a
Signed-off-by: Alexey Nepomnyashih <sdl@nppct.ru>
---
 fs/efivarfs/inode.c    |  3 ++-
 fs/efivarfs/internal.h |  6 +++---
 fs/efivarfs/super.c    | 19 ++++++++++---------
 fs/efivarfs/vars.c     |  5 +++--
 4 files changed, 18 insertions(+), 15 deletions(-)

diff --git a/fs/efivarfs/inode.c b/fs/efivarfs/inode.c
index e93f2afd6741..3b5b956dbf44 100644
--- a/fs/efivarfs/inode.c
+++ b/fs/efivarfs/inode.c
@@ -77,6 +77,7 @@ static bool efivarfs_valid_name(const char *str, int len)
 static int efivarfs_create(struct user_namespace *mnt_userns, struct inode *dir,
 			   struct dentry *dentry, umode_t mode, bool excl)
 {
+	struct efivarfs_fs_info *info = dir->i_sb->s_fs_info;
 	struct inode *inode = NULL;
 	struct efivar_entry *var;
 	int namelen, i = 0, err = 0;
@@ -114,7 +115,7 @@ static int efivarfs_create(struct user_namespace *mnt_userns, struct inode *dir,
 	inode->i_private = var;
 	kmemleak_ignore(var);
 
-	err = efivar_entry_add(var, &efivarfs_list);
+	err = efivar_entry_add(var, &info->efivarfs_list);
 	if (err)
 		goto out;
 
diff --git a/fs/efivarfs/internal.h b/fs/efivarfs/internal.h
index 0762c0a1d207..0abf4bf2bb73 100644
--- a/fs/efivarfs/internal.h
+++ b/fs/efivarfs/internal.h
@@ -16,6 +16,7 @@ struct efivarfs_mount_opts {
 
 struct efivarfs_fs_info {
 	struct efivarfs_mount_opts mount_opts;
+	struct list_head efivarfs_list;
 };
 
 struct efi_variable {
@@ -33,7 +34,8 @@ struct efivar_entry {
 	struct kobject kobj;
 };
 
-int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
+int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *,
+			    struct list_head *),
 		void *data, bool duplicates, struct list_head *head);
 
 int efivar_entry_add(struct efivar_entry *entry, struct list_head *head);
@@ -63,6 +65,4 @@ extern struct inode *efivarfs_get_inode(struct super_block *sb,
 			const struct inode *dir, int mode, dev_t dev,
 			bool is_removable);
 
-extern struct list_head efivarfs_list;
-
 #endif /* EFIVAR_FS_INTERNAL_H */
diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
index b4f1c46ea06f..71d850bdedfa 100644
--- a/fs/efivarfs/super.c
+++ b/fs/efivarfs/super.c
@@ -18,8 +18,6 @@
 
 #include "internal.h"
 
-LIST_HEAD(efivarfs_list);
-
 static void efivarfs_evict_inode(struct inode *inode)
 {
 	clear_inode(inode);
@@ -119,7 +117,8 @@ static struct dentry *efivarfs_alloc_dentry(struct dentry *parent, char *name)
 }
 
 static int efivarfs_callback(efi_char16_t *name16, efi_guid_t vendor,
-			     unsigned long name_size, void *data)
+			     unsigned long name_size, void *data,
+			     struct list_head *list)
 {
 	struct super_block *sb = (struct super_block *)data;
 	struct efivar_entry *entry;
@@ -171,7 +170,7 @@ static int efivarfs_callback(efi_char16_t *name16, efi_guid_t vendor,
 	}
 
 	__efivar_entry_get(entry, NULL, &size, NULL);
-	__efivar_entry_add(entry, &efivarfs_list);
+	__efivar_entry_add(entry, list);
 
 	/* copied by the above to local storage in the dentry. */
 	kfree(name);
@@ -241,6 +240,7 @@ static int efivarfs_parse_param(struct fs_context *fc, struct fs_parameter *para
 
 static int efivarfs_fill_super(struct super_block *sb, struct fs_context *fc)
 {
+	struct efivarfs_fs_info *sfi = sb->s_fs_info;
 	struct inode *inode = NULL;
 	struct dentry *root;
 	int err;
@@ -266,11 +266,10 @@ static int efivarfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	if (!root)
 		return -ENOMEM;
 
-	INIT_LIST_HEAD(&efivarfs_list);
-
-	err = efivar_init(efivarfs_callback, (void *)sb, true, &efivarfs_list);
+	err = efivar_init(efivarfs_callback, (void *)sb, true,
+			  &sfi->efivarfs_list);
 	if (err)
-		efivar_entry_iter(efivarfs_destroy, &efivarfs_list, NULL);
+		efivar_entry_iter(efivarfs_destroy, &sfi->efivarfs_list, NULL);
 
 	return err;
 }
@@ -304,6 +303,8 @@ static int efivarfs_init_fs_context(struct fs_context *fc)
 	if (!sfi)
 		return -ENOMEM;
 
+	INIT_LIST_HEAD(&sfi->efivarfs_list);
+
 	sfi->mount_opts.uid = GLOBAL_ROOT_UID;
 	sfi->mount_opts.gid = GLOBAL_ROOT_GID;
 
@@ -319,7 +320,7 @@ static void efivarfs_kill_sb(struct super_block *sb)
 	kill_litter_super(sb);
 
 	/* Remove all entries and destroy */
-	efivar_entry_iter(efivarfs_destroy, &efivarfs_list, NULL);
+	efivar_entry_iter(efivarfs_destroy, &sfi->efivarfs_list, NULL);
 	kfree(sfi);
 }
 
diff --git a/fs/efivarfs/vars.c b/fs/efivarfs/vars.c
index 13bc60698955..2ad377818d0f 100644
--- a/fs/efivarfs/vars.c
+++ b/fs/efivarfs/vars.c
@@ -369,7 +369,8 @@ static void dup_variable_bug(efi_char16_t *str16, efi_guid_t *vendor_guid,
  *
  * Returns 0 on success, or a kernel error code on failure.
  */
-int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
+int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *,
+			    struct list_head *),
 		void *data, bool duplicates, struct list_head *head)
 {
 	unsigned long variable_name_size = 512;
@@ -421,7 +422,7 @@ int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
 				status = EFI_NOT_FOUND;
 			} else {
 				err = func(variable_name, vendor_guid,
-					   variable_name_size, data);
+					   variable_name_size, data, head);
 				if (err)
 					status = EFI_NOT_FOUND;
 			}
-- 
2.43.0