[PATCH v2 2/2] fuse: Send security context of inode on file creation
Vivek Goyal
vgoyal at redhat.com
Tue Nov 2 15:30:31 UTC 2021
On Tue, Nov 02, 2021 at 03:00:30PM +0100, Miklos Szeredi wrote:
> On Tue, 12 Oct 2021 at 20:06, Vivek Goyal <vgoyal at redhat.com> 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 at chromium.org>
> >
> > 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 at redhat.com>
> > ---
> > 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) {
>
Hi Miklos,
> Instead of a new arg to create_new_entry(), this could check
> args.opcode != FUSE_LINK.
Will do.
>
> > + 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.
Even for the case of FUSE_LINK request? I think I put this check because
FUSE_LINK is not sending secctx header. Other requests are appending
this header even if a security module is not loaded/enabled.
I guess it makes more sense to add secctx header even for FUSE_LINK
request. Just that header will mention 0 security contexts are
following. This will interface more uniform. I will make this change.
>
> > + 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.
I guess I will fold first patch into this one, so that there is only
one 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"?
Sounds good. Will do.
>
> 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.
Agreed. Will add total length also to "fuse_secctx_header". That will
act as a strong check/verification mechanism as well as allow to
quickly skip to next args if one does not want to parse security contexts
for whatever reason.
Thanks
Vivek
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