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[138.88.31.60]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-908323e8bc0sm28991836d6.26.2026.07.30.16.45.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Jul 2026 16:45:41 -0700 (PDT) From: David Windsor To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Jiri Olsa , Kumar Kartikeya Dwivedi , Emil Tsalapatis , Matt Bobrowski , Paul Moore , James Morris , "Serge E . Hallyn" , Casey Schaufler , Stephen Smalley , Ondrej Mosnacek , Mimi Zohar , Roberto Sassu , Dmitry Kasatkin , Eric Snowberg , Alexander Viro , Christian Brauner , Jan Kara , Shuah Khan Cc: bpf@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, selinux@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, David Windsor Subject: [PATCH v6 bpf-next 3/4] bpf: add bpf_init_inode_xattr kfunc for atomic inode labeling Date: Thu, 30 Jul 2026 19:45:32 -0400 Message-ID: <20260730234533.1912709-4-dwindsor@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260730234533.1912709-1-dwindsor@gmail.com> References: <20260730234533.1912709-1-dwindsor@gmail.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add bpf_init_inode_xattr() kfunc for BPF LSM programs to atomically set xattrs via the inode_init_security hook using security_lsmxattr_add(). The hook now passes its xattr state as a single struct lsm_xattrs object, which the kfunc takes directly. This kfunc is only callable from inode_init_security; the verifier rejects attempts to call it elsewhere. A previous attempt [1] required a kmalloc string output protocol for the xattr name. Since commit 6bcdfd2cac55 ("security: Allow all LSMs to provide xattrs for inode_init_security hook") [2], the xattr name is no longer allocated; it is a static constant. Link: https://kernsec.org/pipermail/linux-security-module-archive/2022-October/034878.html [1] Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6bcdfd2cac55 [2] Suggested-by: Song Liu Signed-off-by: David Windsor --- fs/bpf_fs_kfuncs.c | 41 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c index f1863a891db6..7b55073934e0 100644 --- a/fs/bpf_fs_kfuncs.c +++ b/fs/bpf_fs_kfuncs.c @@ -11,7 +11,9 @@ #include #include #include +#include #include +#include __bpf_kfunc_start_defs(); @@ -379,6 +381,44 @@ __bpf_kfunc struct inode *bpf_real_data_inode(struct file *file) return d_real_inode(file_dentry(file)); } +/** + * bpf_init_inode_xattr - set an xattr on a new inode from inode_init_security + * @xattrs: inode_init_security xattr state from the hook context + * @name__str: xattr name (e.g., "bpf.file_label") + * @value_p: dynptr containing the xattr value + * + * Only callable from lsm/inode_init_security programs. + * + * Return: 0 on success, -EOPNOTSUPP if the filesystem does not accept + * xattrs at inode creation, negative error on other failures. + */ +__bpf_kfunc int bpf_init_inode_xattr(struct lsm_xattrs *xattrs, + const char *name__str, + const struct bpf_dynptr *value_p) +{ + struct bpf_dynptr_kern *value_ptr = (struct bpf_dynptr_kern *)value_p; + const void *value; + u32 value_len; + + if (!name__str) + return -EINVAL; + if (strncmp(name__str, XATTR_BPF_LSM_SUFFIX, + sizeof(XATTR_BPF_LSM_SUFFIX) - 1)) + return -EPERM; + + if (!xattrs->xattrs) + return -EOPNOTSUPP; + + value_len = __bpf_dynptr_size(value_ptr); + value = __bpf_dynptr_data(value_ptr, value_len); + if (!value) + return -EINVAL; + + return security_lsmxattr_add(xattrs, LSM_ID_BPF, + name__str + sizeof(XATTR_BPF_LSM_SUFFIX) - 1, + value, value_len); +} + __bpf_kfunc_end_defs(); BTF_KFUNCS_START(bpf_fs_kfunc_set_ids) @@ -390,6 +430,7 @@ BTF_ID_FLAGS(func, bpf_get_file_xattr, KF_SLEEPABLE) BTF_ID_FLAGS(func, bpf_set_dentry_xattr, KF_SLEEPABLE) BTF_ID_FLAGS(func, bpf_remove_dentry_xattr, KF_SLEEPABLE) BTF_ID_FLAGS(func, bpf_real_data_inode, KF_SLEEPABLE | KF_RET_NULL) +BTF_ID_FLAGS(func, bpf_init_inode_xattr) BTF_KFUNCS_END(bpf_fs_kfunc_set_ids) static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id) -- 2.53.0