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Subject: Re: [PATCH -next v2 3/6] landlock: add chmod and chown support
From:   xiujianfeng <xiujianfeng@huawei.com>
To:     <mic@digikod.net>, <paul@paul-moore.com>, <jmorris@namei.org>,
        <serge@hallyn.com>, <shuah@kernel.org>, <corbet@lwn.net>
CC:     <linux-security-module@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <linux-kselftest@vger.kernel.org>,
        <linux-doc@vger.kernel.org>
References: <20220827111215.131442-1-xiujianfeng@huawei.com>
 <20220827111215.131442-4-xiujianfeng@huawei.com>
Message-ID: <1a6b3217-b709-f401-7007-5452648b70a1@huawei.com>
Date:   Mon, 29 Aug 2022 14:35:04 +0800
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Hi,

?? 2022/8/27 19:12, Xiu Jianfeng д??:
> Add two flags LANDLOCK_ACCESS_FS_CHMOD and LANDLOCK_ACCESS_FS_CHGRP to
> support restriction to chmod(2) and chown(2) with landlock.
> 
> If these two access rights are set on a directory, they only take effect
> for its context, not the directory itself.
> 
> This patch also change the landlock ABI version from 3 to 4.
> 
> Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
> ---
>   include/uapi/linux/landlock.h                | 10 +++--
>   security/landlock/fs.c                       | 43 +++++++++++++++++++-
>   security/landlock/limits.h                   |  2 +-
>   security/landlock/syscalls.c                 |  2 +-
>   tools/testing/selftests/landlock/base_test.c |  2 +-
>   tools/testing/selftests/landlock/fs_test.c   |  6 ++-
>   6 files changed, 56 insertions(+), 9 deletions(-)
> 
> diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
> index 735b1fe8326e..07b73626ff20 100644
> --- a/include/uapi/linux/landlock.h
> +++ b/include/uapi/linux/landlock.h
> @@ -141,14 +141,16 @@ struct landlock_path_beneath_attr {
>    *   directory) parent.  Otherwise, such actions are denied with errno set to
>    *   EACCES.  The EACCES errno prevails over EXDEV to let user space
>    *   efficiently deal with an unrecoverable error.
> + * - %LANDLOCK_ACCESS_FS_CHMOD: Change the file mode bits of a file.
> + * - %LANDLOCK_ACCESS_FS_CHGRP: Change the owner and/or group of a file.
>    *
>    * .. warning::
>    *
>    *   It is currently not possible to restrict some file-related actions
>    *   accessible through these syscall families: :manpage:`chdir(2)`,
> - *   :manpage:`stat(2)`, :manpage:`flock(2)`, :manpage:`chmod(2)`,
> - *   :manpage:`chown(2)`, :manpage:`setxattr(2)`, :manpage:`utime(2)`,
> - *   :manpage:`ioctl(2)`, :manpage:`fcntl(2)`, :manpage:`access(2)`.
> + *   :manpage:`stat(2)`, :manpage:`flock(2)`, :manpage:`setxattr(2)`,
> + *   :manpage:`utime(2)`,:manpage:`ioctl(2)`, :manpage:`fcntl(2)`,
> + *   :manpage:`access(2)`.
>    *   Future Landlock evolutions will enable to restrict them.
>    */
>   /* clang-format off */
> @@ -167,6 +169,8 @@ struct landlock_path_beneath_attr {
>   #define LANDLOCK_ACCESS_FS_MAKE_SYM			(1ULL << 12)
>   #define LANDLOCK_ACCESS_FS_REFER			(1ULL << 13)
>   #define LANDLOCK_ACCESS_FS_TRUNCATE			(1ULL << 14)
> +#define LANDLOCK_ACCESS_FS_CHMOD			(1ULL << 15)
> +#define LANDLOCK_ACCESS_FS_CHGRP			(1ULL << 16)
>   /* clang-format on */
>   
>   #endif /* _UAPI_LINUX_LANDLOCK_H */
> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> index 4ef614a4ea22..6ac83d96ada7 100644
> --- a/security/landlock/fs.c
> +++ b/security/landlock/fs.c
> @@ -185,7 +185,9 @@ static struct landlock_object *get_inode_object(struct inode *const inode)
>   	LANDLOCK_ACCESS_FS_EXECUTE | \
>   	LANDLOCK_ACCESS_FS_WRITE_FILE | \
>   	LANDLOCK_ACCESS_FS_READ_FILE | \
> -	LANDLOCK_ACCESS_FS_TRUNCATE)
> +	LANDLOCK_ACCESS_FS_TRUNCATE | \
> +	LANDLOCK_ACCESS_FS_CHMOD | \
> +	LANDLOCK_ACCESS_FS_CHGRP)
>   /* clang-format on */
>   
>   /*
> @@ -690,6 +692,31 @@ static inline int current_check_access_path(const struct path *const path,
>   	return check_access_path(dom, path, access_request);
>   }
>   
> +static inline int
> +current_check_access_path_context_only(const struct path *const path,
> +				       const access_mask_t access_request)
> +{
> +	const struct landlock_ruleset *const dom =
> +		landlock_get_current_domain();
> +	struct path eff_path;
> +	int ret;
> +
> +	if (!dom)
> +		return 0;
> +	eff_path = *path;
> +	/* if it's dir, check its visible parent. */
> +	if (d_is_dir(eff_path.dentry)) {
> +		path_get(&eff_path);
> +		/* dont care if reaches the root or not. */

I may made a mistake here, I think it should return -EACCES directly if 
the walk result is not WALK_CONTINUE.

> +		walk_to_visible_parent(&eff_path);
> +		ret = current_check_access_path(&eff_path, access_request);
> +		path_put(&eff_path);
> +	} else {
> +		ret = current_check_access_path(&eff_path, access_request);
> +	}
> +	return ret;
> +}
> +
>   static inline access_mask_t get_mode_access(const umode_t mode)
>   {
>   	switch (mode & S_IFMT) {
> @@ -1177,6 +1204,18 @@ static int hook_path_truncate(const struct path *const path)
>   	return current_check_access_path(path, LANDLOCK_ACCESS_FS_TRUNCATE);
>   }
>   
> +static int hook_path_chmod(const struct path *const path, umode_t mode)
> +{
> +	return current_check_access_path_context_only(path,
> +					LANDLOCK_ACCESS_FS_CHMOD);
> +}
> +
> +static int hook_path_chown(const struct path *const path, kuid_t uid, kgid_t gid)
> +{
> +	return current_check_access_path_context_only(path,
> +					LANDLOCK_ACCESS_FS_CHGRP);
> +}
> +
>   /* File hooks */
>   
>   static inline access_mask_t get_file_access(const struct file *const file)
> @@ -1230,6 +1269,8 @@ static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
>   	LSM_HOOK_INIT(path_unlink, hook_path_unlink),
>   	LSM_HOOK_INIT(path_rmdir, hook_path_rmdir),
>   	LSM_HOOK_INIT(path_truncate, hook_path_truncate),
> +	LSM_HOOK_INIT(path_chmod, hook_path_chmod),
> +	LSM_HOOK_INIT(path_chown, hook_path_chown),
>   
>   	LSM_HOOK_INIT(file_open, hook_file_open),
>   };
> diff --git a/security/landlock/limits.h b/security/landlock/limits.h
> index 82288f0e9e5e..7cdd7d467d12 100644
> --- a/security/landlock/limits.h
> +++ b/security/landlock/limits.h
> @@ -18,7 +18,7 @@
>   #define LANDLOCK_MAX_NUM_LAYERS		16
>   #define LANDLOCK_MAX_NUM_RULES		U32_MAX
>   
> -#define LANDLOCK_LAST_ACCESS_FS		LANDLOCK_ACCESS_FS_TRUNCATE
> +#define LANDLOCK_LAST_ACCESS_FS		LANDLOCK_ACCESS_FS_CHGRP
>   #define LANDLOCK_MASK_ACCESS_FS		((LANDLOCK_LAST_ACCESS_FS << 1) - 1)
>   #define LANDLOCK_NUM_ACCESS_FS		__const_hweight64(LANDLOCK_MASK_ACCESS_FS)
>   
> diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
> index f4d6fc7ed17f..469e0e11735c 100644
> --- a/security/landlock/syscalls.c
> +++ b/security/landlock/syscalls.c
> @@ -129,7 +129,7 @@ static const struct file_operations ruleset_fops = {
>   	.write = fop_dummy_write,
>   };
>   
> -#define LANDLOCK_ABI_VERSION 3
> +#define LANDLOCK_ABI_VERSION 4
>   
>   /**
>    * sys_landlock_create_ruleset - Create a new ruleset
> diff --git a/tools/testing/selftests/landlock/base_test.c b/tools/testing/selftests/landlock/base_test.c
> index 72cdae277b02..9f00582f639c 100644
> --- a/tools/testing/selftests/landlock/base_test.c
> +++ b/tools/testing/selftests/landlock/base_test.c
> @@ -75,7 +75,7 @@ TEST(abi_version)
>   	const struct landlock_ruleset_attr ruleset_attr = {
>   		.handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE,
>   	};
> -	ASSERT_EQ(3, landlock_create_ruleset(NULL, 0,
> +	ASSERT_EQ(4, landlock_create_ruleset(NULL, 0,
>   					     LANDLOCK_CREATE_RULESET_VERSION));
>   
>   	ASSERT_EQ(-1, landlock_create_ruleset(&ruleset_attr, 0,
> diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
> index debe2d9ea6cf..f513cd8d9d51 100644
> --- a/tools/testing/selftests/landlock/fs_test.c
> +++ b/tools/testing/selftests/landlock/fs_test.c
> @@ -404,9 +404,11 @@ TEST_F_FORK(layout1, inval)
>   	LANDLOCK_ACCESS_FS_EXECUTE | \
>   	LANDLOCK_ACCESS_FS_WRITE_FILE | \
>   	LANDLOCK_ACCESS_FS_READ_FILE | \
> -	LANDLOCK_ACCESS_FS_TRUNCATE)
> +	LANDLOCK_ACCESS_FS_TRUNCATE | \
> +	LANDLOCK_ACCESS_FS_CHMOD | \
> +	LANDLOCK_ACCESS_FS_CHGRP)
>   
> -#define ACCESS_LAST LANDLOCK_ACCESS_FS_TRUNCATE
> +#define ACCESS_LAST LANDLOCK_ACCESS_FS_CHGRP
>   
>   #define ACCESS_ALL ( \
>   	ACCESS_FILE | \
>