On Wed, Sep 13, 2023 at 11:23 AM Miklos Szeredi <[email protected]> wrote:
>
> Add a way to query attributes of a single mount instead of having to parse
> the complete /proc/$PID/mountinfo, which might be huge.
>
> Lookup the mount by the old (32bit) or new (64bit) mount ID. If a mount
> needs to be queried based on path, then statx(2) can be used to first query
> the mount ID belonging to the path.
>
> Design is based on a suggestion by Linus:
>
> "So I'd suggest something that is very much like "statfsat()", which gets
> a buffer and a length, and returns an extended "struct statfs" *AND*
> just a string description at the end."
>
> The interface closely mimics that of statx.
>
> Handle ASCII attributes by appending after the end of the structure (as per
> above suggestion). Allow querying multiple string attributes with
> individual offset/length for each. String are nul terminated (termination
> isn't counted in length).
>
> Mount options are also delimited with nul characters. Unlike proc, special
> characters are not quoted.
>
> Link: https://lore.kernel.org/all/CAHk-=wh5YifP7hzKSbwJj94+DZ2czjrZsczy6GBimiogZws=rg@mail.gmail.com/
> Signed-off-by: Miklos Szeredi <[email protected]>
> ---
> arch/x86/entry/syscalls/syscall_64.tbl | 1 +
> fs/internal.h | 5 +
> fs/namespace.c | 312 ++++++++++++++++++++++++-
> fs/proc_namespace.c | 19 +-
> fs/statfs.c | 1 +
> include/linux/syscalls.h | 3 +
> include/uapi/asm-generic/unistd.h | 5 +-
> include/uapi/linux/mount.h | 36 +++
> 8 files changed, 373 insertions(+), 9 deletions(-)
...
> diff --git a/fs/namespace.c b/fs/namespace.c
> index de47c5f66e17..088a52043bba 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
...
> +static int do_statmnt(struct stmt_state *s)
> +{
> + struct statmnt *sm = &s->sm;
> + struct mount *m = real_mount(s->mnt);
> +
> + if (!capable(CAP_SYS_ADMIN) &&
> + !is_path_reachable(m, m->mnt.mnt_root, &s->root))
> + return -EPERM;
I realize statmnt() is different from fstatfs(), but from an access
control perspective they look a lot alike to me which is why I think
we should probably have a security_sb_statfs() call here. Same thing
for the listmnt() syscall in patch 3/3.
> + stmt_numeric(s, STMT_SB_BASIC, stmt_sb_basic);
> + stmt_numeric(s, STMT_MNT_BASIC, stmt_mnt_basic);
> + stmt_numeric(s, STMT_PROPAGATE_FROM, stmt_propagate_from);
> + stmt_string(s, STMT_MNT_ROOT, stmt_mnt_root, &sm->mnt_root);
> + stmt_string(s, STMT_MOUNTPOINT, stmt_mountpoint, &sm->mountpoint);
> + stmt_string(s, STMT_FS_TYPE, stmt_fs_type, &sm->fs_type);
> + stmt_string(s, STMT_SB_OPTS, stmt_sb_opts, &sm->sb_opts);
> +
> + if (s->err)
> + return s->err;
> +
> + if (copy_to_user(s->buf, sm, min_t(size_t, s->bufsize, sizeof(*sm))))
> + return -EFAULT;
> +
> + return 0;
> +}
--
paul-moore.com
On Thu, 14 Sept 2023 at 22:40, Paul Moore <[email protected]> wrote:
>
> On Wed, Sep 13, 2023 at 11:23 AM Miklos Szeredi <[email protected]> wrote:
> ...
>
> > +static int do_statmnt(struct stmt_state *s)
> > +{
> > + struct statmnt *sm = &s->sm;
> > + struct mount *m = real_mount(s->mnt);
> > +
> > + if (!capable(CAP_SYS_ADMIN) &&
> > + !is_path_reachable(m, m->mnt.mnt_root, &s->root))
> > + return -EPERM;
>
> I realize statmnt() is different from fstatfs(), but from an access
> control perspective they look a lot alike to me which is why I think
> we should probably have a security_sb_statfs() call here. Same thing
> for the listmnt() syscall in patch 3/3.
Okay, makes sense.
Thanks,
Miklos