[PATCH v3 1/1] fuse: Send security context of inode on file creation
Vivek Goyal
vgoyal at redhat.com
Thu Nov 11 14:32:22 UTC 2021
I noticed that this patch is conflicting with some fuse patches
merged in Linus's tree. I will post updated version.
Vivek
On Wed, Nov 10, 2021 at 05:55:28PM -0500, Vivek Goyal 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.
>
> fuse_sectx_header, fuse_secctx, xattr_name, security_context
>
> - struct fuse_secctx_header
> This contains total number of security contexts being sent and total
> size of all the security contexts (including size of fuse_secctx_header).
>
> - struct fuse_secctx.
> This contains 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.
>
> - security context.
> This is the actual security context whose size is specified in fuse_secctx
> struct.
>
> Also add the FUSE_SECURITY_CTX flag for the `flags` field of the
> fuse_init_out struct. When this flag is set the kernel will append the
> security context for a newly created inode to the request (create,
> mkdir, mknod, and symlink). The server is responsible for ensuring that
> the inode appears atomically (preferrably) with the requested security
> context.
>
> For example, If the server is using SELinux and backed by a "real" linux
> file system that supports extended attributes it can write the security
> context value to /proc/thread-self/attr/fscreate before making the syscall
> to create the inode.
>
> This patch is based on patch from Chirantan Ekbote <chirantan at chromium.org>.
>
> Signed-off-by: Vivek Goyal <vgoyal at redhat.com>
> ---
> fs/fuse/dir.c | 103 ++++++++++++++++++++++++++++++++++++++
> fs/fuse/fuse_i.h | 3 ++
> fs/fuse/inode.c | 4 +-
> include/uapi/linux/fuse.h | 31 +++++++++++-
> 4 files changed, 139 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index d9b977c0f38d..69398eb7b325 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 +459,69 @@ 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_secctx_header *fsecctx_header;
> + 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(*fsecctx_header) + 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;
> + fsecctx_header = (struct fuse_secctx_header*) ptr;
> + fsecctx_header->nr_secctx = 1;
> + fsecctx_header->size = full_ctxlen;
> + ptr += sizeof(*fsecctx_header);
> +
> + 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(*fsecctx_header);
> + full_ctx = kzalloc(full_ctxlen, GFP_KERNEL);
> + if (!full_ctx) {
> + err = -ENOMEM;
> + goto out_err;
> + }
> + fsecctx_header = full_ctx;
> + fsecctx_header->size = full_ctxlen;
> + }
> +
> + *security_ctxlen = full_ctxlen;
> + *security_ctx = full_ctx;
> +out_err:
> + return err;
> +}
> +
> /*
> * Atomic create+open operation
> *
> @@ -476,6 +542,8 @@ 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 +585,18 @@ 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 +634,7 @@ 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:
> @@ -620,6 +701,8 @@ static int create_new_entry(struct fuse_mount *fm, struct fuse_args *args,
> 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 +716,27 @@ 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 (fm->fc->init_security && 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;
> +
> + 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;
>
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index f55f9f94b1a4..0d257c4eeb70 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 12d49a1914e8..40c5533243c0 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -1143,6 +1143,8 @@ 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;
> @@ -1186,7 +1188,7 @@ 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 36ed092227fa..710cdf20608d 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
> @@ -184,6 +184,10 @@
> *
> * 7.34
> * - add FUSE_SYNCFS
> + *
> + * 7.35
> + * - add FUSE_SECURITY_CTX flag for fuse_init_out
> + * - add security context to create, mkdir, symlink, and mknod requests
> */
>
> #ifndef _LINUX_FUSE_H
> @@ -219,7 +223,7 @@
> #define FUSE_KERNEL_VERSION 7
>
> /** Minor version number of this interface */
> -#define FUSE_KERNEL_MINOR_VERSION 34
> +#define FUSE_KERNEL_MINOR_VERSION 35
>
> /** The node ID of the root inode */
> #define FUSE_ROOT_ID 1
> @@ -336,6 +340,8 @@ struct fuse_file_lock {
> * write/truncate sgid is killed only if file has group
> * execute permission. (Same as Linux VFS behavior).
> * FUSE_SETXATTR_EXT: Server supports extended struct fuse_setxattr_in
> + * FUSE_SECURITY_CTX: add security context to create, mkdir, symlink, and
> + * mknod
> */
> #define FUSE_ASYNC_READ (1 << 0)
> #define FUSE_POSIX_LOCKS (1 << 1)
> @@ -367,6 +373,7 @@ struct fuse_file_lock {
> #define FUSE_SUBMOUNTS (1 << 27)
> #define FUSE_HANDLE_KILLPRIV_V2 (1 << 28)
> #define FUSE_SETXATTR_EXT (1 << 29)
> +#define FUSE_SECURITY_CTX (1 << 30)
>
> /**
> * CUSE INIT request/reply flags
> @@ -979,4 +986,26 @@ 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 and what's the total size of all security contexts (including
> + * size of fuse_secctx_header).
> + *
> + */
> +struct fuse_secctx_header {
> + uint32_t size;
> + uint32_t nr_secctx;
> +};
> +
> #endif /* _LINUX_FUSE_H */
> --
> 2.31.1
>
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