[PATCH v4 bpf-next 0/3] bpf: add bpf_init_inode_xattr kfunc for atomic inode labeling

[PATCH v4 bpf-next 0/3] bpf: add bpf_init_inode_xattr kfunc for atomic inode labeling

[David Windsor]

Many in-kernel LSMs (SELinux, Smack, IMA) store security labels in
extended attributes. For these LSMs, atomic labeling during inode
creation is critical: if the inode becomes accessible before its xattr
is set, it is briefly unlabeled, which can disrupt LSMs making policy
decisions based on file labels.

Existing LSMs solve this by setting xattrs directly in the
inode_init_security hook, which runs before the inode becomes
accessible. BPF LSM programs currently lack this capability because
the hook uses an output parameter (xattr_count) that BPF programs
cannot write to, and existing kfuncs like bpf_set_dentry_xattr
require a dentry that isn't available until after the inode is
accessible.

This series introduces the bpf_init_inode_xattr() kfunc, which takes
the combined inode_init_security xattr context argument to access
xattrs and xattr_count, and internally writes to xattr_count via
lsm_get_xattr_slot().

v4:
  - introduce struct lsm_xattrs in separate patch (Alexei, Paul)
  - rename struct xattr_ctx to struct lsm_xattrs (Paul)
  - make lsm_xattrs.xattr_count unsigned int (Paul)
  - drop new_xattrs/xattr_count locals in
    security_inode_init_security() (Paul)
  - fold __bpf_init_inode_xattr() into bpf_init_inode_xattr() (Paul)
  - drop bpf_fs_kfuncs_filter() attach-point check; rely on verifier
    type enforcement (Alexei)
  - drop attach-time cap; enforce slot budget in the kfunc (Alexei)
  - allocate the combined xattr with GFP_NOFS (sashiko-bot)
  - replace init_inode_xattr_attach_cap selftest with runtime
    init_inode_xattr_slot_limit

v3:
  - rename struct lsm_xattr_ctx to struct xattr_ctx (Paul)
  - increase BPF_LSM_INODE_INIT_XATTRS to 4 (Song)
  - enforce per-hook attachment cap at attach time to prevent
    runtime rejection (Paul)
  - add init_inode_xattr_attach_cap selftest

v2:
  - pass the xattr state as a combined context object and drop the
    verifier fixup path (Kumar)
  - restrict bpf_init_inode_xattr labels to bpf.* namespace (Matt)
  - cap bpf_init_inode_xattr() at BPF_LSM_INODE_INIT_XATTRS slots per
    invocation (AI)

David Windsor (3):
  security: pass inode_init_security xattrs via struct lsm_xattrs
  bpf: add bpf_init_inode_xattr kfunc for atomic inode labeling
  selftests/bpf: add tests for bpf_init_inode_xattr kfunc

 fs/bpf_fs_kfuncs.c                            |  79 +++++++++++
 include/linux/bpf_lsm.h                       |   3 +
 include/linux/evm.h                           |   9 +-
 include/linux/lsm_hook_defs.h                 |   4 +-
 include/linux/lsm_hooks.h                     |  16 +--
 include/linux/security.h                      |   5 +
 kernel/bpf/bpf_lsm.c                          |   1 +
 security/bpf/hooks.c                          |   1 +
 security/integrity/evm/evm_main.c             |   8 +-
 security/security.c                           |  24 ++--
 security/selinux/hooks.c                      |   4 +-
 security/smack/smack_lsm.c                    |  27 ++--
 tools/testing/selftests/bpf/bpf_kfuncs.h      |   5 +
 .../selftests/bpf/prog_tests/lsm_kfuncs.c     | 129 ++++++++++++++++++
 .../bpf/progs/test_init_inode_xattr.c         |  31 +++++
 15 files changed, 299 insertions(+), 47 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/lsm_kfuncs.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_init_inode_xattr.c


base-commit: e771677c937da5808f7b6c1f0e4a97ec1a84f8a8
-- 
2.53.0

[PATCH v4 bpf-next 1/3] security: pass inode_init_security xattrs via struct lsm_xattrs

[David Windsor]

inode_init_security receives the LSM xattr array and its count as
separate parameters. For better compatibility with the bpf verifier,
update inode_init_security and its callers to consolidate these
parameters into a single context object: struct lsm_xattrs.

Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 include/linux/evm.h               |  9 +++++----
 include/linux/lsm_hook_defs.h     |  4 ++--
 include/linux/lsm_hooks.h         | 16 +++++++---------
 include/linux/security.h          |  5 +++++
 security/integrity/evm/evm_main.c |  8 +++++---
 security/security.c               | 24 ++++++++++++------------
 security/selinux/hooks.c          |  4 ++--
 security/smack/smack_lsm.c        | 27 ++++++++++++---------------
 8 files changed, 50 insertions(+), 47 deletions(-)

diff --git a/include/linux/evm.h b/include/linux/evm.h
index 913f4573b203..528f360f3308 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h
@@ -12,6 +12,8 @@
 #include <linux/integrity.h>
 #include <linux/xattr.h>
 
+struct lsm_xattrs;
+
 #ifdef CONFIG_EVM
 extern int evm_set_key(void *key, size_t keylen);
 extern enum integrity_status evm_verifyxattr(struct dentry *dentry,
@@ -21,8 +23,8 @@ extern enum integrity_status evm_verifyxattr(struct dentry *dentry,
 int evm_fix_hmac(struct dentry *dentry, const char *xattr_name,
 		 const char *xattr_value, size_t xattr_value_len);
 int evm_inode_init_security(struct inode *inode, struct inode *dir,
-			    const struct qstr *qstr, struct xattr *xattrs,
-			    int *xattr_count);
+			    const struct qstr *qstr,
+			    struct lsm_xattrs *xattrs);
 extern bool evm_revalidate_status(const char *xattr_name);
 extern int evm_protected_xattr_if_enabled(const char *req_xattr_name);
 extern int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
@@ -63,8 +65,7 @@ static inline int evm_fix_hmac(struct dentry *dentry, const char *xattr_name,
 
 static inline int evm_inode_init_security(struct inode *inode, struct inode *dir,
 					  const struct qstr *qstr,
-					  struct xattr *xattrs,
-					  int *xattr_count)
+					  struct lsm_xattrs *xattrs)
 {
 	return 0;
 }
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 65c9609ec207..5b2de7865ce8 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -116,8 +116,8 @@ LSM_HOOK(int, 0, inode_alloc_security, struct inode *inode)
 LSM_HOOK(void, LSM_RET_VOID, inode_free_security, struct inode *inode)
 LSM_HOOK(void, LSM_RET_VOID, inode_free_security_rcu, void *inode_security)
 LSM_HOOK(int, -EOPNOTSUPP, inode_init_security, struct inode *inode,
-	 struct inode *dir, const struct qstr *qstr, struct xattr *xattrs,
-	 int *xattr_count)
+	 struct inode *dir, const struct qstr *qstr,
+	 struct lsm_xattrs *xattrs)
 LSM_HOOK(int, 0, inode_init_security_anon, struct inode *inode,
 	 const struct qstr *name, const struct inode *context_inode)
 LSM_HOOK(int, 0, inode_create, struct inode *dir, struct dentry *dentry,
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index b4f8cad53ddb..7afe06a8d4c6 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -200,20 +200,18 @@ extern struct lsm_static_calls_table static_calls_table __ro_after_init;
 
 /**
  * lsm_get_xattr_slot - Return the next available slot and increment the index
- * @xattrs: array storing LSM-provided xattrs
- * @xattr_count: number of already stored xattrs (updated)
+ * @ctx: xattr state shared by inode_init_security hooks
  *
- * Retrieve the first available slot in the @xattrs array to fill with an xattr,
- * and increment @xattr_count.
+ * Retrieve the first available slot in the @ctx->xattrs array to fill with an
+ * xattr, and increment @ctx->xattr_count.
  *
- * Return: The slot to fill in @xattrs if non-NULL, NULL otherwise.
+ * Return: The slot to fill in @ctx->xattrs if non-NULL, NULL otherwise.
  */
-static inline struct xattr *lsm_get_xattr_slot(struct xattr *xattrs,
-					       int *xattr_count)
+static inline struct xattr *lsm_get_xattr_slot(struct lsm_xattrs *ctx)
 {
-	if (unlikely(!xattrs))
+	if (unlikely(!ctx || !ctx->xattrs))
 		return NULL;
-	return &xattrs[(*xattr_count)++];
+	return &ctx->xattrs[ctx->xattr_count++];
 }
 
 #endif /* ! __LINUX_LSM_HOOKS_H */
diff --git a/include/linux/security.h b/include/linux/security.h
index 153e9043058f..0be590c40689 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -68,6 +68,11 @@ struct watch;
 struct watch_notification;
 struct lsm_ctx;
 
+struct lsm_xattrs {
+	struct xattr *xattrs;
+	unsigned int xattr_count;
+};
+
 /* Default (no) options for the capable function */
 #define CAP_OPT_NONE 0x0
 /* If capable should audit the security request */
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index b59e3f121b8a..b7158fc63543 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -1062,14 +1062,16 @@ static int evm_inode_copy_up_xattr(struct dentry *src, const char *name)
  * evm_inode_init_security - initializes security.evm HMAC value
  */
 int evm_inode_init_security(struct inode *inode, struct inode *dir,
-			    const struct qstr *qstr, struct xattr *xattrs,
-			    int *xattr_count)
+			    const struct qstr *qstr,
+			    struct lsm_xattrs *lsm_xattrs)
 {
 	struct evm_xattr *xattr_data;
 	struct xattr *xattr, *evm_xattr;
+	struct xattr *xattrs;
 	bool evm_protected_xattrs = false;
 	int rc;
 
+	xattrs = lsm_xattrs ? lsm_xattrs->xattrs : NULL;
 	if (!(evm_initialized & EVM_INIT_HMAC) || !xattrs)
 		return 0;
 
@@ -1087,7 +1089,7 @@ int evm_inode_init_security(struct inode *inode, struct inode *dir,
 	if (!evm_protected_xattrs)
 		return 0;
 
-	evm_xattr = lsm_get_xattr_slot(xattrs, xattr_count);
+	evm_xattr = lsm_get_xattr_slot(lsm_xattrs);
 	/*
 	 * Array terminator (xattr name = NULL) must be the first non-filled
 	 * xattr slot.
diff --git a/security/security.c b/security/security.c
index 71aea8fdf014..2ad7f09c1a61 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1333,8 +1333,8 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 				 const initxattrs initxattrs, void *fs_data)
 {
 	struct lsm_static_call *scall;
-	struct xattr *new_xattrs = NULL;
-	int ret = -EOPNOTSUPP, xattr_count = 0;
+	struct lsm_xattrs xattrs = {};
+	int ret = -EOPNOTSUPP;
 
 	if (unlikely(IS_PRIVATE(inode)))
 		return 0;
@@ -1344,15 +1344,15 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 
 	if (initxattrs) {
 		/* Allocate +1 as terminator. */
-		new_xattrs = kcalloc(blob_sizes.lbs_xattr_count + 1,
-				     sizeof(*new_xattrs), GFP_NOFS);
-		if (!new_xattrs)
+		xattrs.xattrs = kcalloc(blob_sizes.lbs_xattr_count + 1,
+					sizeof(*xattrs.xattrs), GFP_NOFS);
+		if (!xattrs.xattrs)
 			return -ENOMEM;
 	}
 
 	lsm_for_each_hook(scall, inode_init_security) {
-		ret = scall->hl->hook.inode_init_security(inode, dir, qstr, new_xattrs,
-						  &xattr_count);
+		ret = scall->hl->hook.inode_init_security(inode, dir, qstr,
+							  &xattrs);
 		if (ret && ret != -EOPNOTSUPP)
 			goto out;
 		/*
@@ -1364,14 +1364,14 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 	}
 
 	/* If initxattrs() is NULL, xattr_count is zero, skip the call. */
-	if (!xattr_count)
+	if (!xattrs.xattr_count)
 		goto out;
 
-	ret = initxattrs(inode, new_xattrs, fs_data);
+	ret = initxattrs(inode, xattrs.xattrs, fs_data);
 out:
-	for (; xattr_count > 0; xattr_count--)
-		kfree(new_xattrs[xattr_count - 1].value);
-	kfree(new_xattrs);
+	for (; xattrs.xattr_count > 0; xattrs.xattr_count--)
+		kfree(xattrs.xattrs[xattrs.xattr_count - 1].value);
+	kfree(xattrs.xattrs);
 	return (ret == -EOPNOTSUPP) ? 0 : ret;
 }
 EXPORT_SYMBOL(security_inode_init_security);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 1a713d96206f..6bba6b212e17 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2962,7 +2962,7 @@ static int selinux_dentry_create_files_as(struct dentry *dentry, int mode,
 
 static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
 				       const struct qstr *qstr,
-				       struct xattr *xattrs, int *xattr_count)
+				       struct lsm_xattrs *xattrs)
 {
 	const struct cred_security_struct *crsec = selinux_cred(current_cred());
 	struct superblock_security_struct *sbsec;
@@ -2992,7 +2992,7 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
 	    !(sbsec->flags & SBLABEL_MNT))
 		return -EOPNOTSUPP;
 
-	xattr = lsm_get_xattr_slot(xattrs, xattr_count);
+	xattr = lsm_get_xattr_slot(xattrs);
 	if (xattr) {
 		rc = security_sid_to_context_force(newsid,
 						   &context, &clen);
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index ff115068c5c0..4501078430ca 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -981,10 +981,10 @@ smk_rule_transmutes(struct smack_known *subject,
 }
 
 static int
-xattr_dupval(struct xattr *xattrs, int *xattr_count,
+xattr_dupval(struct lsm_xattrs *xattrs,
 	     const char *name, const void *value, unsigned int vallen)
 {
-	struct xattr * const xattr = lsm_get_xattr_slot(xattrs, xattr_count);
+	struct xattr * const xattr = lsm_get_xattr_slot(xattrs);
 
 	if (!xattr)
 		return 0;
@@ -1003,14 +1003,13 @@ xattr_dupval(struct xattr *xattrs, int *xattr_count,
  * @inode: the newly created inode
  * @dir: containing directory object
  * @qstr: unused
- * @xattrs: where to put the attributes
- * @xattr_count: current number of LSM-provided xattrs (updated)
+ * @xattrs: where to put attributes and update count
  *
  * Returns 0 if it all works out, -ENOMEM if there's no memory
  */
 static int smack_inode_init_security(struct inode *inode, struct inode *dir,
 				     const struct qstr *qstr,
-				     struct xattr *xattrs, int *xattr_count)
+				     struct lsm_xattrs *xattrs)
 {
 	struct task_smack *tsp = smack_cred(current_cred());
 	struct inode_smack * const issp = smack_inode(inode);
@@ -1057,21 +1056,19 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
 		if (S_ISDIR(inode->i_mode)) {
 			transflag = SMK_INODE_TRANSMUTE;
 
-			if (xattr_dupval(xattrs, xattr_count,
-				XATTR_SMACK_TRANSMUTE,
-				TRANS_TRUE,
-				TRANS_TRUE_SIZE
-			))
+			if (xattr_dupval(xattrs,
+					 XATTR_SMACK_TRANSMUTE,
+					 TRANS_TRUE,
+					 TRANS_TRUE_SIZE))
 				rc = -ENOMEM;
 		}
 	}
 
 	if (rc == 0)
-		if (xattr_dupval(xattrs, xattr_count,
-			    XATTR_SMACK_SUFFIX,
-			    issp->smk_inode->smk_known,
-		     strlen(issp->smk_inode->smk_known)
-		))
+		if (xattr_dupval(xattrs,
+				 XATTR_SMACK_SUFFIX,
+				 issp->smk_inode->smk_known,
+				 strlen(issp->smk_inode->smk_known)))
 			rc = -ENOMEM;
 instant_inode:
 	issp->smk_flags |= (SMK_INODE_INSTANT | transflag);
-- 
2.53.0

[PATCH v4 bpf-next 2/3] bpf: add bpf_init_inode_xattr kfunc for atomic inode labeling

[David Windsor]

Add bpf_init_inode_xattr() kfunc for BPF LSM programs to atomically set
xattrs via the inode_init_security hook using lsm_get_xattr_slot(). The
hook now passes its xattr state as a single struct lsm_xattrs object,
which the kfunc takes directly.

The kfunc is only usable from lsm/inode_init_security programs: no other
hook exposes a struct lsm_xattrs argument, so the verifier rejects calls
from elsewhere. Restrict the xattr names that may be set via this kfunc
to the bpf.* namespace.

BPF reserves BPF_LSM_INODE_INIT_XATTRS slots via lbs_xattr_count, and the
kfunc enforces that BPF never consumes more slots than it reserved,
returning -ENOSPC once the budget is exhausted.

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]
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 fs/bpf_fs_kfuncs.c      | 79 +++++++++++++++++++++++++++++++++++++++++
 include/linux/bpf_lsm.h |  3 ++
 kernel/bpf/bpf_lsm.c    |  1 +
 security/bpf/hooks.c    |  1 +
 4 files changed, 84 insertions(+)

diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
index 768aca2dc0f0..c4023c82f21e 100644
--- a/fs/bpf_fs_kfuncs.c
+++ b/fs/bpf_fs_kfuncs.c
@@ -10,6 +10,7 @@
 #include <linux/fsnotify.h>
 #include <linux/file.h>
 #include <linux/kernfs.h>
+#include <linux/lsm_hooks.h>
 #include <linux/mm.h>
 #include <linux/xattr.h>
 
@@ -374,6 +375,83 @@ __bpf_kfunc struct inode *bpf_real_inode(struct dentry *dentry)
 	return d_real_inode(dentry);
 }
 
+static int bpf_xattrs_used(const struct lsm_xattrs *ctx)
+{
+	const size_t prefix_len = sizeof(XATTR_BPF_LSM_SUFFIX) - 1;
+	unsigned int i, n = 0;
+
+	for (i = 0; i < ctx->xattr_count; i++) {
+		const char *name = ctx->xattrs[i].name;
+
+		if (name && !strncmp(name, XATTR_BPF_LSM_SUFFIX, prefix_len))
+			n++;
+	}
+	return n;
+}
+
+/**
+ * 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, negative error on failure.
+ */
+__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;
+	size_t name_len;
+	void *xattr_value;
+	struct xattr *xattr;
+	const void *value;
+	u32 value_len;
+
+	if (!xattrs || !xattrs->xattrs || !name__str)
+		return -EINVAL;
+	if (bpf_xattrs_used(xattrs) >= BPF_LSM_INODE_INIT_XATTRS)
+		return -ENOSPC;
+
+	name_len = strlen(name__str);
+	if (name_len == 0 || name_len > XATTR_NAME_MAX)
+		return -EINVAL;
+	if (strncmp(name__str, XATTR_BPF_LSM_SUFFIX,
+		    sizeof(XATTR_BPF_LSM_SUFFIX) - 1))
+		return -EPERM;
+
+	value_len = __bpf_dynptr_size(value_ptr);
+	if (value_len == 0 || value_len > XATTR_SIZE_MAX)
+		return -EINVAL;
+
+	value = __bpf_dynptr_data(value_ptr, value_len);
+	if (!value)
+		return -EINVAL;
+
+	/* Combine xattr value + name into one allocation. */
+	xattr_value = kmalloc(value_len + name_len + 1, GFP_NOFS);
+	if (!xattr_value)
+		return -ENOMEM;
+
+	memcpy(xattr_value, value, value_len);
+	memcpy(xattr_value + value_len, name__str, name_len);
+	((char *)xattr_value)[value_len + name_len] = '\0';
+
+	xattr = lsm_get_xattr_slot(xattrs);
+	if (!xattr) {
+		kfree(xattr_value);
+		return -ENOSPC;
+	}
+
+	xattr->value = xattr_value;
+	xattr->name = (const char *)xattr_value + value_len;
+	xattr->value_len = value_len;
+
+	return 0;
+}
+
 __bpf_kfunc_end_defs();
 
 BTF_KFUNCS_START(bpf_fs_kfunc_set_ids)
@@ -385,6 +463,7 @@ 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_inode, KF_SLEEPABLE | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_init_inode_xattr, KF_SLEEPABLE)
 BTF_KFUNCS_END(bpf_fs_kfunc_set_ids)
 
 static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)
diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
index 143775a27a2a..b655c708818e 100644
--- a/include/linux/bpf_lsm.h
+++ b/include/linux/bpf_lsm.h
@@ -19,6 +19,9 @@
 #include <linux/lsm_hook_defs.h>
 #undef LSM_HOOK
 
+/* max bpf xattrs per inode */
+#define BPF_LSM_INODE_INIT_XATTRS 4
+
 struct bpf_storage_blob {
 	struct bpf_local_storage __rcu *storage;
 };
diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
index 564071a92d7d..1c3f84a92420 100644
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c
@@ -315,6 +315,7 @@ BTF_ID(func, bpf_lsm_inode_create)
 BTF_ID(func, bpf_lsm_inode_free_security)
 BTF_ID(func, bpf_lsm_inode_getattr)
 BTF_ID(func, bpf_lsm_inode_getxattr)
+BTF_ID(func, bpf_lsm_inode_init_security)
 BTF_ID(func, bpf_lsm_inode_mknod)
 BTF_ID(func, bpf_lsm_inode_need_killpriv)
 BTF_ID(func, bpf_lsm_inode_post_setxattr)
diff --git a/security/bpf/hooks.c b/security/bpf/hooks.c
index 40efde233f3a..d7c44c5c0e30 100644
--- a/security/bpf/hooks.c
+++ b/security/bpf/hooks.c
@@ -30,6 +30,7 @@ static int __init bpf_lsm_init(void)
 
 struct lsm_blob_sizes bpf_lsm_blob_sizes __ro_after_init = {
 	.lbs_inode = sizeof(struct bpf_storage_blob),
+	.lbs_xattr_count = BPF_LSM_INODE_INIT_XATTRS,
 };
 
 DEFINE_LSM(bpf) = {
-- 
2.53.0

Re: [PATCH v4 bpf-next 2/3] bpf: add bpf_init_inode_xattr kfunc for atomic inode labeling

[David Windsor]

On Thu, Jun 25, 2026 at 7:23 AM Christian Brauner <brauner@kernel.org> wrote:
<snip>
>
> We expose a bunch of VFS heavy operations for various security modules
> and this is really not different. For xattrs we have it all centralized
> in the VFS and in general all VFS related bpf kfuncs should continue
> living there and be registered there. Anything that's just bpf infra
> specific can go to security/bpf/kfuncs.c instead. But anyway, it's a bpf
> specific helper so it's the bpf maintainer's call.

After Alexei's requested changes removing the attach-time checks,
there's really not much left to go in an LSM-specific kfuncs file. The
bpf infra plumbing for registering the kfunc and bpf_xattrs_used()
seem to be the only LSM-specific bits aside from the kfunc.

I am willing to put this code anywhere. I've tried to CC all involved
in all 3 patches, even though there's some split in concerns.

Re: [PATCH v4 bpf-next 2/3] bpf: add bpf_init_inode_xattr kfunc for atomic inode labeling

[Paul Moore]

On Tue, Jun 30, 2026 at 2:40 PM David Windsor <dwindsor@gmail.com> wrote:
>
> Add bpf_init_inode_xattr() kfunc for BPF LSM programs to atomically set
> xattrs via the inode_init_security hook using lsm_get_xattr_slot(). The
> hook now passes its xattr state as a single struct lsm_xattrs object,
> which the kfunc takes directly.
>
> The kfunc is only usable from lsm/inode_init_security programs: no other
> hook exposes a struct lsm_xattrs argument, so the verifier rejects calls
> from elsewhere. Restrict the xattr names that may be set via this kfunc
> to the bpf.* namespace.
>
> BPF reserves BPF_LSM_INODE_INIT_XATTRS slots via lbs_xattr_count, and the
> kfunc enforces that BPF never consumes more slots than it reserved,
> returning -ENOSPC once the budget is exhausted.
>
> 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]
> Signed-off-by: David Windsor <dwindsor@gmail.com>
> ---
>  fs/bpf_fs_kfuncs.c      | 79 +++++++++++++++++++++++++++++++++++++++++
>  include/linux/bpf_lsm.h |  3 ++
>  kernel/bpf/bpf_lsm.c    |  1 +
>  security/bpf/hooks.c    |  1 +
>  4 files changed, 84 insertions(+)
>
> diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
> index 768aca2dc0f0..c4023c82f21e 100644
> --- a/fs/bpf_fs_kfuncs.c
> +++ b/fs/bpf_fs_kfuncs.c
> @@ -10,6 +10,7 @@
>  #include <linux/fsnotify.h>
>  #include <linux/file.h>
>  #include <linux/kernfs.h>
> +#include <linux/lsm_hooks.h>
>  #include <linux/mm.h>
>  #include <linux/xattr.h>
>
> @@ -374,6 +375,83 @@ __bpf_kfunc struct inode *bpf_real_inode(struct dentry *dentry)
>         return d_real_inode(dentry);
>  }
>
> +static int bpf_xattrs_used(const struct lsm_xattrs *ctx)
> +{
> +       const size_t prefix_len = sizeof(XATTR_BPF_LSM_SUFFIX) - 1;
> +       unsigned int i, n = 0;
> +
> +       for (i = 0; i < ctx->xattr_count; i++) {
> +               const char *name = ctx->xattrs[i].name;
> +
> +               if (name && !strncmp(name, XATTR_BPF_LSM_SUFFIX, prefix_len))
> +                       n++;
> +       }
> +       return n;
> +}
> +
> +/**
> + * 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, negative error on failure.
> + */
> +__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;
> +       size_t name_len;
> +       void *xattr_value;
> +       struct xattr *xattr;
> +       const void *value;
> +       u32 value_len;
> +
> +       if (!xattrs || !xattrs->xattrs || !name__str)
> +               return -EINVAL;
> +       if (bpf_xattrs_used(xattrs) >= BPF_LSM_INODE_INIT_XATTRS)
> +               return -ENOSPC;
> +
> +       name_len = strlen(name__str);
> +       if (name_len == 0 || name_len > XATTR_NAME_MAX)
> +               return -EINVAL;
> +       if (strncmp(name__str, XATTR_BPF_LSM_SUFFIX,
> +                   sizeof(XATTR_BPF_LSM_SUFFIX) - 1))
> +               return -EPERM;
> +
> +       value_len = __bpf_dynptr_size(value_ptr);
> +       if (value_len == 0 || value_len > XATTR_SIZE_MAX)
> +               return -EINVAL;
> +
> +       value = __bpf_dynptr_data(value_ptr, value_len);
> +       if (!value)
> +               return -EINVAL;
> +
> +       /* Combine xattr value + name into one allocation. */
> +       xattr_value = kmalloc(value_len + name_len + 1, GFP_NOFS);
> +       if (!xattr_value)
> +               return -ENOMEM;
> +
> +       memcpy(xattr_value, value, value_len);
> +       memcpy(xattr_value + value_len, name__str, name_len);
> +       ((char *)xattr_value)[value_len + name_len] = '\0';
> +
> +       xattr = lsm_get_xattr_slot(xattrs);
> +       if (!xattr) {
> +               kfree(xattr_value);
> +               return -ENOSPC;
> +       }
> +
> +       xattr->value = xattr_value;
> +       xattr->name = (const char *)xattr_value + value_len;
> +       xattr->value_len = value_len;
> +
> +       return 0;
> +}

This is not a generic VFS function, it is a LSM specific function, it
belongs under security/, please move the code as discussed previously.

--
paul-moore.com

Re: [PATCH v4 bpf-next 2/3] bpf: add bpf_init_inode_xattr kfunc for atomic inode labeling

[Alexei Starovoitov]

On Tue Jun 30, 2026 at 12:20 PM PDT, Paul Moore wrote:
>> +__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;
>> +       size_t name_len;
>> +       void *xattr_value;
>> +       struct xattr *xattr;
>> +       const void *value;
>> +       u32 value_len;
>> +
>> +       if (!xattrs || !xattrs->xattrs || !name__str)
>> +               return -EINVAL;
>> +       if (bpf_xattrs_used(xattrs) >= BPF_LSM_INODE_INIT_XATTRS)
>> +               return -ENOSPC;
>> +
>> +       name_len = strlen(name__str);
>> +       if (name_len == 0 || name_len > XATTR_NAME_MAX)
>> +               return -EINVAL;
>> +       if (strncmp(name__str, XATTR_BPF_LSM_SUFFIX,
>> +                   sizeof(XATTR_BPF_LSM_SUFFIX) - 1))
>> +               return -EPERM;
>> +
>> +       value_len = __bpf_dynptr_size(value_ptr);
>> +       if (value_len == 0 || value_len > XATTR_SIZE_MAX)
>> +               return -EINVAL;
>> +
>> +       value = __bpf_dynptr_data(value_ptr, value_len);
>> +       if (!value)
>> +               return -EINVAL;
>> +
>> +       /* Combine xattr value + name into one allocation. */
>> +       xattr_value = kmalloc(value_len + name_len + 1, GFP_NOFS);
>> +       if (!xattr_value)
>> +               return -ENOMEM;
>> +
>> +       memcpy(xattr_value, value, value_len);
>> +       memcpy(xattr_value + value_len, name__str, name_len);
>> +       ((char *)xattr_value)[value_len + name_len] = '\0';
>> +
>> +       xattr = lsm_get_xattr_slot(xattrs);
>> +       if (!xattr) {
>> +               kfree(xattr_value);
>> +               return -ENOSPC;
>> +       }
>> +
>> +       xattr->value = xattr_value;
>> +       xattr->name = (const char *)xattr_value + value_len;
>> +       xattr->value_len = value_len;
>> +
>> +       return 0;
>> +}
>
> This is not a generic VFS function, it is a LSM specific function, it
> belongs under security/, please move the code as discussed previously.

Paul,
Not quite. It's all about xattrs.
Having "struct lsm_xattrs" in the arguments doesn't make it lsm related.
You needs to study existing kfuncs and tracepoints.
A bunch of them have "*lsm*" in the arguments.

All,
CI found issues, so this set needs another respin.
After that it's hopefully good to go.

David,
you're on the right track. The patchset is getting close.
Thank you for working on it.

Re: [PATCH v4 bpf-next 2/3] bpf: add bpf_init_inode_xattr kfunc for atomic inode labeling

[Paul Moore]

On Wed, Jul 1, 2026 at 2:09 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
> On Tue Jun 30, 2026 at 12:20 PM PDT, Paul Moore wrote:
> >> +__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;
> >> +       size_t name_len;
> >> +       void *xattr_value;
> >> +       struct xattr *xattr;
> >> +       const void *value;
> >> +       u32 value_len;
> >> +
> >> +       if (!xattrs || !xattrs->xattrs || !name__str)
> >> +               return -EINVAL;
> >> +       if (bpf_xattrs_used(xattrs) >= BPF_LSM_INODE_INIT_XATTRS)
> >> +               return -ENOSPC;
> >> +
> >> +       name_len = strlen(name__str);
> >> +       if (name_len == 0 || name_len > XATTR_NAME_MAX)
> >> +               return -EINVAL;
> >> +       if (strncmp(name__str, XATTR_BPF_LSM_SUFFIX,
> >> +                   sizeof(XATTR_BPF_LSM_SUFFIX) - 1))
> >> +               return -EPERM;
> >> +
> >> +       value_len = __bpf_dynptr_size(value_ptr);
> >> +       if (value_len == 0 || value_len > XATTR_SIZE_MAX)
> >> +               return -EINVAL;
> >> +
> >> +       value = __bpf_dynptr_data(value_ptr, value_len);
> >> +       if (!value)
> >> +               return -EINVAL;
> >> +
> >> +       /* Combine xattr value + name into one allocation. */
> >> +       xattr_value = kmalloc(value_len + name_len + 1, GFP_NOFS);
> >> +       if (!xattr_value)
> >> +               return -ENOMEM;
> >> +
> >> +       memcpy(xattr_value, value, value_len);
> >> +       memcpy(xattr_value + value_len, name__str, name_len);
> >> +       ((char *)xattr_value)[value_len + name_len] = '\0';
> >> +
> >> +       xattr = lsm_get_xattr_slot(xattrs);
> >> +       if (!xattr) {
> >> +               kfree(xattr_value);
> >> +               return -ENOSPC;
> >> +       }
> >> +
> >> +       xattr->value = xattr_value;
> >> +       xattr->name = (const char *)xattr_value + value_len;
> >> +       xattr->value_len = value_len;
> >> +
> >> +       return 0;
> >> +}
> >
> > This is not a generic VFS function, it is a LSM specific function, it
> > belongs under security/, please move the code as discussed previously.
>
> Paul,
> Not quite. It's all about xattrs.
> Having "struct lsm_xattrs" in the arguments doesn't make it lsm related.
> You needs to study existing kfuncs and tracepoints.
> A bunch of them have "*lsm*" in the arguments.

Alexei,

I'm sorry you don't understand the basics of the LSM concept, but
please look at evm_inode_init_security(), xattr_dupval(), and
selinux_inode_init_security() for some background.  There should not
be any usage of lsm_get_xattr_slot() or BPF_LSM_INODE_INIT_XATTRS
outside of security/; you argued a similar idea to justify your NACK
of Hornet, I'm simply applying the same logic here.  We also have the
very recent security issue caused by the BPF subsystem which failed to
acknowledge that the admin disabled the BPF LSM and then walked all
over kernel memory when it shouldn't.  Moving LSM internals outside of
the LSM creates an environment where flaws like this can go
undetected.

As I said previously, if you absolutely insist on the kfunc being in
the VFS kfunc file, the LSM specific bits need to be abstracted out
into an LSM function.

  kfunc bpf_init_inode_xattr(...)
  {
    /* sanity check params */
    if (!xattrs ...)
      return -EINVAL;

   /* get value/len from bpf dynptr */

   /* hook will check for LSM specific xattr count/limits, allocate,
copy value*/
   rc = security_lsmxattr_add(xattrs, LSM_ID_BPF, value, value_len);
   if (rc)
     return rc;
  }

David, if you like I can provide you a patch that implements the
security_lsmxattr_add() hook above if you aren't comfortable writing
that, but if you want to give it a shot that's all the better :)

-- 
paul-moore.com

Re: [PATCH v4 bpf-next 2/3] bpf: add bpf_init_inode_xattr kfunc for atomic inode labeling

[Paul Moore]

On Wed, Jul 1, 2026 at 8:55 AM Paul Moore <paul@paul-moore.com> wrote:
> On Wed, Jul 1, 2026 at 2:09 AM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> > On Tue Jun 30, 2026 at 12:20 PM PDT, Paul Moore wrote:
> > >> +__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;
> > >> +       size_t name_len;
> > >> +       void *xattr_value;
> > >> +       struct xattr *xattr;
> > >> +       const void *value;
> > >> +       u32 value_len;
> > >> +
> > >> +       if (!xattrs || !xattrs->xattrs || !name__str)
> > >> +               return -EINVAL;
> > >> +       if (bpf_xattrs_used(xattrs) >= BPF_LSM_INODE_INIT_XATTRS)
> > >> +               return -ENOSPC;
> > >> +
> > >> +       name_len = strlen(name__str);
> > >> +       if (name_len == 0 || name_len > XATTR_NAME_MAX)
> > >> +               return -EINVAL;
> > >> +       if (strncmp(name__str, XATTR_BPF_LSM_SUFFIX,
> > >> +                   sizeof(XATTR_BPF_LSM_SUFFIX) - 1))
> > >> +               return -EPERM;
> > >> +
> > >> +       value_len = __bpf_dynptr_size(value_ptr);
> > >> +       if (value_len == 0 || value_len > XATTR_SIZE_MAX)
> > >> +               return -EINVAL;
> > >> +
> > >> +       value = __bpf_dynptr_data(value_ptr, value_len);
> > >> +       if (!value)
> > >> +               return -EINVAL;
> > >> +
> > >> +       /* Combine xattr value + name into one allocation. */
> > >> +       xattr_value = kmalloc(value_len + name_len + 1, GFP_NOFS);
> > >> +       if (!xattr_value)
> > >> +               return -ENOMEM;
> > >> +
> > >> +       memcpy(xattr_value, value, value_len);
> > >> +       memcpy(xattr_value + value_len, name__str, name_len);
> > >> +       ((char *)xattr_value)[value_len + name_len] = '\0';
> > >> +
> > >> +       xattr = lsm_get_xattr_slot(xattrs);
> > >> +       if (!xattr) {
> > >> +               kfree(xattr_value);
> > >> +               return -ENOSPC;
> > >> +       }
> > >> +
> > >> +       xattr->value = xattr_value;
> > >> +       xattr->name = (const char *)xattr_value + value_len;
> > >> +       xattr->value_len = value_len;
> > >> +
> > >> +       return 0;
> > >> +}
> > >
> > > This is not a generic VFS function, it is a LSM specific function, it
> > > belongs under security/, please move the code as discussed previously.
> >
> > Paul,
> > Not quite. It's all about xattrs.
> > Having "struct lsm_xattrs" in the arguments doesn't make it lsm related.
> > You needs to study existing kfuncs and tracepoints.
> > A bunch of them have "*lsm*" in the arguments.
>
> Alexei,
>
> I'm sorry you don't understand the basics of the LSM concept, but
> please look at evm_inode_init_security(), xattr_dupval(), and
> selinux_inode_init_security() for some background.  There should not
> be any usage of lsm_get_xattr_slot() or BPF_LSM_INODE_INIT_XATTRS
> outside of security/; you argued a similar idea to justify your NACK
> of Hornet, I'm simply applying the same logic here.  We also have the
> very recent security issue caused by the BPF subsystem which failed to
> acknowledge that the admin disabled the BPF LSM and then walked all
> over kernel memory when it shouldn't.  Moving LSM internals outside of
> the LSM creates an environment where flaws like this can go
> undetected.
>
> As I said previously, if you absolutely insist on the kfunc being in
> the VFS kfunc file, the LSM specific bits need to be abstracted out
> into an LSM function.
>
>   kfunc bpf_init_inode_xattr(...)
>   {
>     /* sanity check params */
>     if (!xattrs ...)
>       return -EINVAL;
>
>    /* get value/len from bpf dynptr */
>
>    /* hook will check for LSM specific xattr count/limits, allocate,
> copy value*/
>    rc = security_lsmxattr_add(xattrs, LSM_ID_BPF, value, value_len);
>    if (rc)
>      return rc;
>   }
>
> David, if you like I can provide you a patch that implements the
> security_lsmxattr_add() hook above if you aren't comfortable writing
> that, but if you want to give it a shot that's all the better :)

One other thing - as this patchset is primarily LSM related, it needs
to be merged via the LSM tree.  If Alexei can't tolerate the LSM tree
merging a minor BPF patch he can either choose to pull from an LSM
tree topic branch or we can merge the LSM infrastructure bits now and
he can merge the BPF changes when the LSM bits hit Linus' tree.

-- 
paul-moore.com

[PATCH v4 bpf-next 3/3] selftests/bpf: add tests for bpf_init_inode_xattr kfunc

[David Windsor]

Test bpf atomic inode xattr labeling in inode_init_security.

Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 tools/testing/selftests/bpf/bpf_kfuncs.h      |   5 +
 .../selftests/bpf/prog_tests/fs_kfuncs.c      | 117 ++++++++++++++++++
 .../bpf/progs/test_init_inode_xattr.c         |  31 +++++
 3 files changed, 153 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/test_init_inode_xattr.c

diff --git a/tools/testing/selftests/bpf/bpf_kfuncs.h b/tools/testing/selftests/bpf/bpf_kfuncs.h
index ae71e9b69051..2639f9f94195 100644
--- a/tools/testing/selftests/bpf/bpf_kfuncs.h
+++ b/tools/testing/selftests/bpf/bpf_kfuncs.h
@@ -92,4 +92,9 @@ extern int bpf_set_dentry_xattr(struct dentry *dentry, const char *name__str,
 				const struct bpf_dynptr *value_p, int flags) __ksym __weak;
 extern int bpf_remove_dentry_xattr(struct dentry *dentry, const char *name__str) __ksym __weak;
 
+struct lsm_xattrs;
+extern int bpf_init_inode_xattr(struct lsm_xattrs *xattrs,
+				const char *name__str,
+				const struct bpf_dynptr *value_p) __ksym __weak;
+
 #endif
diff --git a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
index 43a26ec69a8e..8b2e0d433aea 100644
--- a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
+++ b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
@@ -10,6 +10,7 @@
 #include "test_get_xattr.skel.h"
 #include "test_set_remove_xattr.skel.h"
 #include "test_fsverity.skel.h"
+#include "test_init_inode_xattr.skel.h"
 
 static const char testfile[] = "/tmp/test_progs_fs_kfuncs";
 
@@ -268,6 +269,116 @@ static void test_fsverity(void)
 	remove(testfile);
 }
 
+static void test_init_inode_xattr(void)
+{
+	struct test_init_inode_xattr *skel = NULL;
+	int fd = -1, err;
+	char value_out[64];
+	const char *testfile_new = "/tmp/test_progs_fs_kfuncs_new";
+
+	skel = test_init_inode_xattr__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "test_init_inode_xattr__open_and_load"))
+		return;
+
+	skel->bss->monitored_pid = getpid();
+	err = test_init_inode_xattr__attach(skel);
+	if (!ASSERT_OK(err, "test_init_inode_xattr__attach"))
+		goto out;
+
+	/* Trigger inode_init_security */
+	fd = open(testfile_new, O_CREAT | O_RDWR, 0644);
+	if (!ASSERT_GE(fd, 0, "create_file"))
+		goto out;
+
+	ASSERT_EQ(skel->data->init_result, 0, "init_result");
+
+	/* initxattrs prepends "security." to the name. */
+	err = getxattr(testfile_new, "security.bpf.test_label", value_out,
+		       sizeof(value_out));
+	if (err < 0 && errno == ENODATA) {
+		printf("%s:SKIP:filesystem did not apply LSM xattrs\n",
+		       __func__);
+		test__skip();
+		goto out;
+	}
+	if (!ASSERT_GE(err, 0, "getxattr"))
+		goto out;
+
+	ASSERT_EQ(err, (int)sizeof(skel->data->xattr_value), "xattr_size");
+	ASSERT_EQ(strncmp(value_out, "unconfined_u:object_r:user_home_t:s0",
+			  sizeof("unconfined_u:object_r:user_home_t:s0")), 0,
+		  "xattr_value");
+
+out:
+	close(fd);
+	test_init_inode_xattr__destroy(skel);
+	remove(testfile_new);
+}
+
+/* Keep in sync with BPF_LSM_INODE_INIT_XATTRS in include/linux/bpf_lsm.h. */
+#define INIT_INODE_XATTR_MAX 4
+
+/*
+ * Programs may attach to inode_init_security without an attach-time limit, but
+ * the kfunc only lets BPF claim INIT_INODE_XATTR_MAX xattr slots per inode.
+ * Calls beyond that budget are rejected at runtime with -ENOSPC.
+ */
+static void test_init_inode_xattr_slot_limit(void)
+{
+	struct test_init_inode_xattr *skel[INIT_INODE_XATTR_MAX + 1] = {};
+	struct bpf_link *link[INIT_INODE_XATTR_MAX + 1] = {};
+	const char *testfile_slot = "/tmp/test_progs_fs_kfuncs_slot";
+	int ok = 0, nospc = 0, other = 0;
+	int i, fd = -1;
+
+	/* All programs attach successfully; there is no attach-time cap. */
+	for (i = 0; i <= INIT_INODE_XATTR_MAX; i++) {
+		skel[i] = test_init_inode_xattr__open_and_load();
+		if (!ASSERT_OK_PTR(skel[i], "open_and_load"))
+			goto out;
+
+		skel[i]->bss->monitored_pid = getpid();
+
+		link[i] = bpf_program__attach_lsm(skel[i]->progs.test_init_inode_xattr);
+		if (!ASSERT_OK_PTR(link[i], "attach"))
+			goto out;
+	}
+
+	/* Trigger inode_init_security once with all programs attached. */
+	fd = open(testfile_slot, O_CREAT | O_RDWR, 0644);
+	if (!ASSERT_GE(fd, 0, "create_file"))
+		goto out;
+
+	/*
+	 * Exactly INIT_INODE_XATTR_MAX programs claim a slot; the program past
+	 * the budget gets -ENOSPC. The order in which programs run is not
+	 * guaranteed, so count results instead of indexing.
+	 */
+	for (i = 0; i <= INIT_INODE_XATTR_MAX; i++) {
+		int res = skel[i]->data->init_result;
+
+		if (res == 0)
+			ok++;
+		else if (res == -ENOSPC)
+			nospc++;
+		else
+			other++;
+	}
+
+	ASSERT_EQ(ok, INIT_INODE_XATTR_MAX, "slots_within_budget");
+	ASSERT_EQ(nospc, 1, "slot_over_budget");
+	ASSERT_EQ(other, 0, "unexpected_result");
+
+out:
+	if (fd >= 0)
+		close(fd);
+	for (i = 0; i <= INIT_INODE_XATTR_MAX; i++) {
+		bpf_link__destroy(link[i]);
+		test_init_inode_xattr__destroy(skel[i]);
+	}
+	remove(testfile_slot);
+}
+
 void test_fs_kfuncs(void)
 {
 	/* Matches xattr_names in progs/test_get_xattr.c */
@@ -288,4 +399,10 @@ void test_fs_kfuncs(void)
 
 	if (test__start_subtest("fsverity"))
 		test_fsverity();
+
+	if (test__start_subtest("init_inode_xattr"))
+		test_init_inode_xattr();
+
+	if (test__start_subtest("init_inode_xattr_slot_limit"))
+		test_init_inode_xattr_slot_limit();
 }
diff --git a/tools/testing/selftests/bpf/progs/test_init_inode_xattr.c b/tools/testing/selftests/bpf/progs/test_init_inode_xattr.c
new file mode 100644
index 000000000000..cb378db957aa
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_init_inode_xattr.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Cisco Systems, Inc. */
+
+#include "vmlinux.h"
+#include <bpf/bpf_tracing.h>
+#include "bpf_kfuncs.h"
+
+char _license[] SEC("license") = "GPL";
+
+__u32 monitored_pid;
+int init_result = -1;
+
+static const char xattr_name[] = "bpf.test_label";
+char xattr_value[] = "unconfined_u:object_r:user_home_t:s0";
+
+SEC("lsm.s/inode_init_security")
+int BPF_PROG(test_init_inode_xattr, struct inode *inode, struct inode *dir,
+	     const struct qstr *qstr, struct lsm_xattrs *xattrs)
+{
+	struct bpf_dynptr value_ptr;
+	__u32 pid;
+
+	pid = bpf_get_current_pid_tgid() >> 32;
+	if (pid != monitored_pid)
+		return 0;
+
+	bpf_dynptr_from_mem(xattr_value, sizeof(xattr_value), 0, &value_ptr);
+	init_result = bpf_init_inode_xattr(xattrs, xattr_name, &value_ptr);
+
+	return 0;
+}
-- 
2.53.0