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Message-ID: <CAMj1kXFRaMgPi1X-WRMkunBhBqfVFyDZu6f7CdCh6mU5Mtqh1A@mail.gmail.com>
Date: Wed, 6 Sep 2023 09:06:29 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Jiao Zhou <jiaozhou@...gle.com>
Cc: Christian Brauner <brauner@...nel.org>,
Linux FS Development <linux-fsdevel@...r.kernel.org>,
Jeremy Kerr <jk@...abs.org>, linux-efi@...r.kernel.org,
linux-kernel@...r.kernel.org,
kernel test robot <oliver.sang@...el.com>
Subject: Re: [PATCH] kernel: Add Mount Option For Efivarfs
On Tue, 5 Sept 2023 at 20:05, Jiao Zhou <jiaozhou@...gle.com> wrote:
>
> Hi Christian,
>
> Thanks for your reply, will adding a guid and uid check like the below be sufficient? I saw this is how most file systems check their gid and uid. I am not quite sure about how to send fd back to init_user_ns. Can you please clarify a little bit? Thank you so much.
...
>
Please don't top post and please only send plaintext email to the mailing lists.
Please consult Documentation/process/submitting-patches.rst in the
Linux source tree if you are unfamiliar with the upstream contribution
process (and since you appear to be at Google, you might want to
consult go/kernel-upstream as well)
Thanks,
Ard.
>
>
> On Mon, Sep 4, 2023 at 1:17 PM Christian Brauner <brauner@...nel.org> wrote:
>>
>> On Thu, Aug 31, 2023 at 03:31:07PM +0000, Jiao Zhou wrote:
>> > Add uid and gid in efivarfs's mount option, so that
>> > we can mount the file system with ownership. This approach
>> > is used by a number of other filesystems that don't have
>> > native support for ownership.
>> >
>> > TEST=FEATURES=test emerge-reven chromeos-kernel-5_15
>> >
>> > Signed-off-by: Jiao Zhou <jiaozhou@...gle.com>
>> > Reported-by: kernel test robot <oliver.sang@...el.com>
>> > Closes: https://lore.kernel.org/oe-lkp/202308291443.ea96ac66-oliver.sang@intel.com
>> > ---
>> > fs/efivarfs/inode.c | 4 +++
>> > fs/efivarfs/internal.h | 9 ++++++
>> > fs/efivarfs/super.c | 65 ++++++++++++++++++++++++++++++++++++++++++
>> > 3 files changed, 78 insertions(+)
>> >
>> > diff --git a/fs/efivarfs/inode.c b/fs/efivarfs/inode.c
>> > index 939e5e242b98..de57fb6c28e1 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->i_ctime = current_time(inode);
>> > diff --git a/fs/efivarfs/internal.h b/fs/efivarfs/internal.h
>> > index 30ae44cb7453..57deaf56d8e2 100644
>> > --- a/fs/efivarfs/internal.h
>> > +++ b/fs/efivarfs/internal.h
>> > @@ -8,6 +8,15 @@
>> >
>> > #include <linux/list.h>
>> >
>> > +struct efivarfs_mount_opts {
>> > + kuid_t uid;
>> > + kgid_t gid;
>> > +};
>> > +
>> > +struct efivarfs_fs_info {
>> > + struct efivarfs_mount_opts mount_opts;
>> > +};
>> > +
>> > extern const struct file_operations efivarfs_file_operations;
>> > extern const struct inode_operations efivarfs_dir_inode_operations;
>> > extern bool efivarfs_valid_name(const char *str, int len);
>> > diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
>> > index 15880a68faad..d67b0d157ff5 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>
>> > @@ -23,10 +24,27 @@ 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;
>> > +
>> > + /* Show partition info */
>> > + 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,
>> > };
>> >
>> > /*
>> > @@ -190,6 +208,41 @@ 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);
>> > + break;
>> > + case Opt_gid:
>> > + opts->gid = make_kgid(current_user_ns(), result.uint_32);
>> > + break;
>>
>> This will allow the following:
>>
>> # initial user namespace
>> fd_fs = fsopen("efivarfs")
>>
>> # switch to some unprivileged userns
>> fsconfig(fd_fs, FSCONFIG_SET_STRING, "uid", "1000")
>> ==> This now resolves within the caller's user namespace which might
>> have an idmapping where 1000 cannot be resolved causing sb->{g,u}id
>> to be set to INVALID_{G,U}ID.
>>
>> In fact this is also possible in your patch right now without the
>> namespace switching. The caller could just pass -1 and that would
>> cause inodes with INVALID_{G,U}ID to be created.
>> So you want a check for {g,u}id_valid().
>>
>> # send fd back to init_user_ns
>> fsconfig(fd_fs, FSCONFIG_CMD_CREATE)
>> fd_mnt = fsmount(fd_fs, ...)
>> move_mount(fd_fs, "", -EBADF, "/somehwere", ...)
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