On Tue, 12 Oct 2021 at 20:06, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
>
> When a new inode is created, send its security context to server along
> with creation request (FUSE_CREAT, FUSE_MKNOD, FUSE_MKDIR and FUSE_SYMLINK).
> This gives server an opportunity to create new file and set security
> context (possibly atomically). In all the configurations it might not
> be possible to set context atomically.
>
> Like nfs and ceph, use security_dentry_init_security() to dermine security
> context of inode and send it with create, mkdir, mknod, and symlink requests.
>
> Following is the information sent to server.
>
> - struct fuse_secctxs.
> This contains total number of security contexts being sent.
>
> - struct fuse_secctx.
> This contains total size of security context which follows this structure.
> There is one fuse_secctx instance per security context.
>
> - xattr name string.
> This string represents name of xattr which should be used while setting
> security context. As of now it is hardcoded to "security.selinux".
>
> - security context.
> This is the actual security context whose size is specified in fuse_secctx
> struct.
>
> This patch is modified version of patch from
> Chirantan Ekbote <chirantan@xxxxxxxxxxxx>
>
> v2:
> - Added "fuse_secctxs" structure where one can specify how many security
> contexts are being sent. This can be useful down the line if we
> have more than one security contexts being set.
>
> Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
> ---
> fs/fuse/dir.c | 115 ++++++++++++++++++++++++++++++++++++--
> fs/fuse/fuse_i.h | 3 +
> fs/fuse/inode.c | 4 +-
> include/uapi/linux/fuse.h | 20 +++++++
> 4 files changed, 136 insertions(+), 6 deletions(-)
>
> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index d9b977c0f38d..ce62593a61f9 100644
> --- a/fs/fuse/dir.c
> +++ b/fs/fuse/dir.c
> @@ -17,6 +17,9 @@
> #include <linux/xattr.h>
> #include <linux/iversion.h>
> #include <linux/posix_acl.h>
> +#include <linux/security.h>
> +#include <linux/types.h>
> +#include <linux/kernel.h>
>
> static void fuse_advise_use_readdirplus(struct inode *dir)
> {
> @@ -456,6 +459,66 @@ static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
> return ERR_PTR(err);
> }
>
> +static int get_security_context(struct dentry *entry, umode_t mode,
> + void **security_ctx, u32 *security_ctxlen)
> +{
> + struct fuse_secctx *fsecctx;
> + struct fuse_secctxs *fsecctxs;
> + void *ctx, *full_ctx;
> + u32 ctxlen, full_ctxlen;
> + int err = 0;
> + const char *name;
> +
> + err = security_dentry_init_security(entry, mode, &entry->d_name,
> + &name, &ctx, &ctxlen);
> + if (err) {
> + if (err != -EOPNOTSUPP)
> + goto out_err;
> + /* No LSM is supporting this security hook. Ignore error */
> + err = 0;
> + ctxlen = 0;
> + }
> +
> + if (ctxlen > 0) {
> + void *ptr;
> +
> + full_ctxlen = sizeof(*fsecctxs) + sizeof(*fsecctx) +
> + strlen(name) + ctxlen + 1;
> + full_ctx = kzalloc(full_ctxlen, GFP_KERNEL);
> + if (!full_ctx) {
> + err = -ENOMEM;
> + kfree(ctx);
> + goto out_err;
> + }
> +
> + ptr = full_ctx;
> + fsecctxs = (struct fuse_secctxs*) ptr;
> + fsecctxs->nr_secctx = 1;
> + ptr += sizeof(*fsecctxs);
> +
> + fsecctx = (struct fuse_secctx*) ptr;
> + fsecctx->size = ctxlen;
> + ptr += sizeof(*fsecctx);
> +
> + strcpy(ptr, name);
> + ptr += strlen(name) + 1;
> + memcpy(ptr, ctx, ctxlen);
> + kfree(ctx);
> + } else {
> + full_ctxlen = sizeof(*fsecctxs);
> + full_ctx = kzalloc(full_ctxlen, GFP_KERNEL);
> + if (!full_ctx) {
> + err = -ENOMEM;
> + goto out_err;
> + }
> + }
> +
> + *security_ctxlen = full_ctxlen;
> + *security_ctx = full_ctx;
> +out_err:
> + return err;
> +}
> +
> /*
> * Atomic create+open operation
> *
> @@ -476,6 +539,8 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
> struct fuse_entry_out outentry;
> struct fuse_inode *fi;
> struct fuse_file *ff;
> + void *security_ctx = NULL;
> + u32 security_ctxlen;
>
> /* Userspace expects S_IFREG in create mode */
> BUG_ON((mode & S_IFMT) != S_IFREG);
> @@ -517,6 +582,18 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
> args.out_args[0].value = &outentry;
> args.out_args[1].size = sizeof(outopen);
> args.out_args[1].value = &outopen;
> +
> + if (fm->fc->init_security) {
> + err = get_security_context(entry, mode, &security_ctx,
> + &security_ctxlen);
> + if (err)
> + goto out_put_forget_req;
> +
> + args.in_numargs = 3;
> + args.in_args[2].size = security_ctxlen;
> + args.in_args[2].value = security_ctx;
> + }
> +
> err = fuse_simple_request(fm, &args);
> if (err)
> goto out_free_ff;
> @@ -554,6 +631,7 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
>
> out_free_ff:
> fuse_file_free(ff);
> + kfree(security_ctx);
> out_put_forget_req:
> kfree(forget);
> out_err:
> @@ -613,13 +691,15 @@ static int fuse_atomic_open(struct inode *dir, struct dentry *entry,
> */
> static int create_new_entry(struct fuse_mount *fm, struct fuse_args *args,
> struct inode *dir, struct dentry *entry,
> - umode_t mode)
> + umode_t mode, bool init_security)
> {
> struct fuse_entry_out outarg;
> struct inode *inode;
> struct dentry *d;
> int err;
> struct fuse_forget_link *forget;
> + void *security_ctx = NULL;
> + u32 security_ctxlen = 0;
>
> if (fuse_is_bad(dir))
> return -EIO;
> @@ -633,7 +713,29 @@ static int create_new_entry(struct fuse_mount *fm, struct fuse_args *args,
> args->out_numargs = 1;
> args->out_args[0].size = sizeof(outarg);
> args->out_args[0].value = &outarg;
> +
> + if (init_security) {
Instead of a new arg to create_new_entry(), this could check
args.opcode != FUSE_LINK.
> + unsigned short idx = args->in_numargs;
> +
> + if ((size_t)idx >= ARRAY_SIZE(args->in_args)) {
> + err = -ENOMEM;
> + goto out_put_forget_req;
> + }
> +
> + err = get_security_context(entry, mode, &security_ctx,
> + &security_ctxlen);
> + if (err)
> + goto out_put_forget_req;
> +
> + if (security_ctxlen > 0) {
This doesn't seem right. How would the server know if this is arg is missing?
I think if FUSE_SECURITY_CTX was negotiated, then the secctx header
will always need to be added to the MK* requests.
> + args->in_args[idx].size = security_ctxlen;
> + args->in_args[idx].value = security_ctx;
> + args->in_numargs++;
> + }
> + }
> +
> err = fuse_simple_request(fm, args);
> + kfree(security_ctx);
> if (err)
> goto out_put_forget_req;
>
> @@ -691,7 +793,7 @@ static int fuse_mknod(struct user_namespace *mnt_userns, struct inode *dir,
> args.in_args[0].value = &inarg;
> args.in_args[1].size = entry->d_name.len + 1;
> args.in_args[1].value = entry->d_name.name;
> - return create_new_entry(fm, &args, dir, entry, mode);
> + return create_new_entry(fm, &args, dir, entry, mode, fm->fc->init_security);
> }
>
> static int fuse_create(struct user_namespace *mnt_userns, struct inode *dir,
> @@ -719,7 +821,8 @@ static int fuse_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
> args.in_args[0].value = &inarg;
> args.in_args[1].size = entry->d_name.len + 1;
> args.in_args[1].value = entry->d_name.name;
> - return create_new_entry(fm, &args, dir, entry, S_IFDIR);
> + return create_new_entry(fm, &args, dir, entry, S_IFDIR,
> + fm->fc->init_security);
> }
>
> static int fuse_symlink(struct user_namespace *mnt_userns, struct inode *dir,
> @@ -735,7 +838,8 @@ static int fuse_symlink(struct user_namespace *mnt_userns, struct inode *dir,
> args.in_args[0].value = entry->d_name.name;
> args.in_args[1].size = len;
> args.in_args[1].value = link;
> - return create_new_entry(fm, &args, dir, entry, S_IFLNK);
> + return create_new_entry(fm, &args, dir, entry, S_IFLNK,
> + fm->fc->init_security);
> }
>
> void fuse_update_ctime(struct inode *inode)
> @@ -915,7 +1019,8 @@ static int fuse_link(struct dentry *entry, struct inode *newdir,
> args.in_args[0].value = &inarg;
> args.in_args[1].size = newent->d_name.len + 1;
> args.in_args[1].value = newent->d_name.name;
> - err = create_new_entry(fm, &args, newdir, newent, inode->i_mode);
> + err = create_new_entry(fm, &args, newdir, newent, inode->i_mode,
> + false);
> /* Contrary to "normal" filesystems it can happen that link
> makes two "logical" inodes point to the same "physical"
> inode. We invalidate the attributes of the old one, so it
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index 319596df5dc6..885f34f9967f 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -765,6 +765,9 @@ struct fuse_conn {
> /* Propagate syncfs() to server */
> unsigned int sync_fs:1;
>
> + /* Initialize security xattrs when creating a new inode */
> + unsigned int init_security:1;
> +
> /** The number of requests waiting for completion */
> atomic_t num_waiting;
>
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 36cd03114b6d..343bc9cfbd92 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -1152,6 +1152,8 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
> }
> if (arg->flags & FUSE_SETXATTR_EXT)
> fc->setxattr_ext = 1;
> + if (arg->flags & FUSE_SECURITY_CTX)
> + fc->init_security = 1;
> } else {
> ra_pages = fc->max_read / PAGE_SIZE;
> fc->no_lock = 1;
> @@ -1195,7 +1197,7 @@ void fuse_send_init(struct fuse_mount *fm)
> FUSE_PARALLEL_DIROPS | FUSE_HANDLE_KILLPRIV | FUSE_POSIX_ACL |
> FUSE_ABORT_ERROR | FUSE_MAX_PAGES | FUSE_CACHE_SYMLINKS |
> FUSE_NO_OPENDIR_SUPPORT | FUSE_EXPLICIT_INVAL_DATA |
> - FUSE_HANDLE_KILLPRIV_V2 | FUSE_SETXATTR_EXT;
> + FUSE_HANDLE_KILLPRIV_V2 | FUSE_SETXATTR_EXT | FUSE_SECURITY_CTX;
> #ifdef CONFIG_FUSE_DAX
> if (fm->fc->dax)
> ia->in.flags |= FUSE_MAP_ALIGNMENT;
> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> index 2fe54c80051a..b31a0f79fde8 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
I don't see why the API changes are split between the first and the
second patch in the series. Please either move all API changes to
1/2 or fold 1/2 into this patch.
> @@ -986,4 +986,24 @@ struct fuse_syncfs_in {
> uint64_t padding;
> };
>
> +/*
> + * For each security context, send fuse_secctx with size of security context
> + * fuse_secctx will be followed by security context name and this in turn
> + * will be followed by actual context label.
> + * fuse_secctx, name, context
> + * */
> +struct fuse_secctx {
> + uint32_t size;
> + uint32_t padding;
> +};
> +
> +/*
> + * Contains the information about how many fuse_secctx structures are being
> + * sent.
> + */
> +struct fuse_secctxs {
> + uint32_t nr_secctx;
> + uint32_t padding;
> +};
The name of this struct is very confusing due to similarity with
fuse_secctx. How about "fuse_secctx_header"?
Also I'd add the total length of the security context (including the
header), otherwise further args would need to parse the security
context completely to find the position of the next arg. The
counterexample is null-terminated names; while parsing these is pretty
trivial, in hindsight it would probably have been better to add a
header to names as well.
Thanks,
Miklos
