On Sat, Feb 26, 2022 at 05:13:31AM IST, Hao Luo wrote:
> This patch allows bpf_syscall prog to perform some basic filesystem
> operations: create, remove directories and unlink files. Three bpf
> helpers are added for this purpose. When combined with the following
> patches that allow pinning and getting bpf objects from bpf prog,
> this feature can be used to create directory hierarchy in bpffs that
> help manage bpf objects purely using bpf progs.
>
> The added helpers subject to the same permission checks as their syscall
> version. For example, one can not write to a read-only file system;
> The identity of the current process is checked to see whether it has
> sufficient permission to perform the operations.
>
> Only directories and files in bpffs can be created or removed by these
> helpers. But it won't be too hard to allow these helpers to operate
> on files in other filesystems, if we want.
>
> Signed-off-by: Hao Luo <haoluo@xxxxxxxxxx>
> ---
> include/linux/bpf.h | 1 +
> include/uapi/linux/bpf.h | 26 +++++
> kernel/bpf/inode.c | 9 +-
> kernel/bpf/syscall.c | 177 +++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 26 +++++
> 5 files changed, 236 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index f19abc59b6cd..fce5e26179f5 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1584,6 +1584,7 @@ int bpf_link_new_fd(struct bpf_link *link);
> struct file *bpf_link_new_file(struct bpf_link *link, int *reserved_fd);
> struct bpf_link *bpf_link_get_from_fd(u32 ufd);
>
> +bool bpf_path_is_bpf_dir(const struct path *path);
> int bpf_obj_pin_user(u32 ufd, const char __user *pathname);
> int bpf_obj_get_user(const char __user *pathname, int flags);
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index afe3d0d7f5f2..a5dbc794403d 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5086,6 +5086,29 @@ union bpf_attr {
> * Return
> * 0 on success, or a negative error in case of failure. On error
> * *dst* buffer is zeroed out.
> + *
> + * long bpf_mkdir(const char *pathname, int pathname_sz, u32 mode)
> + * Description
> + * Attempts to create a directory name *pathname*. The argument
> + * *pathname_sz* specifies the length of the string *pathname*.
> + * The argument *mode* specifies the mode for the new directory. It
> + * is modified by the process's umask. It has the same semantic as
> + * the syscall mkdir(2).
> + * Return
> + * 0 on success, or a negative error in case of failure.
> + *
> + * long bpf_rmdir(const char *pathname, int pathname_sz)
> + * Description
> + * Deletes a directory, which must be empty.
> + * Return
> + * 0 on sucess, or a negative error in case of failure.
> + *
> + * long bpf_unlink(const char *pathname, int pathname_sz)
> + * Description
> + * Deletes a name and possibly the file it refers to. It has the
> + * same semantic as the syscall unlink(2).
> + * Return
> + * 0 on success, or a negative error in case of failure.
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -5280,6 +5303,9 @@ union bpf_attr {
> FN(xdp_load_bytes), \
> FN(xdp_store_bytes), \
> FN(copy_from_user_task), \
> + FN(mkdir), \
> + FN(rmdir), \
> + FN(unlink), \
> /* */
>
How about only introducing bpf_sys_mkdirat and bpf_sys_unlinkat? That would be
more useful for other cases in future, and when AT_FDCWD is passed, has the same
functionality as these, but when openat/fget is supported, it would work
relative to other dirfds as well. It can also allow using dirfd of the process
calling read for a iterator (e.g. if it sets the fd number using skel->bss).
unlinkat's AT_REMOVEDIR flag also removes the need for a bpf_rmdir.
WDYT?
> [...]
--
Kartikeya
