Merge branch 'add-bpf_get_dentry_xattr'

Song Liu says:

====================
Add bpf_get_dentry_xattr

Add a kfunc to read xattr from dentry. Also add selftest for the new
kfunc.

Changes v3 => v4:
1. Fix selftest build.

V3: https://lore.kernel.org/bpf/20240806203340.3503805-1-song@kernel.org/T/#u

Changes v2 => v3:
1. Move the kfuncs to fs/bpf_fs_kfuncs.c.
2. Fix selftests build error on s390. (Alexei)

v2: https://lore.kernel.org/bpf/20240730230805.42205-1-song@kernel.org/T/#u

Changes v1 => v2:
1. Remove 3 kfuncs that are ready yet.

v1: https://lore.kernel.org/linux-fsdevel/20240725234706.655613-1-song@kernel.org/T/#u
====================

Link: https://lore.kernel.org/r/20240806230904.71194-1-song@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

fs/bpf_fs_kfuncs.c

@@ -8,6 +8,7 @@
 #include <linux/fs.h>
 #include <linux/file.h>
 #include <linux/mm.h>
+#include <linux/xattr.h>
 
 __bpf_kfunc_start_defs();
 
@@ -92,6 +93,65 @@ __bpf_kfunc int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz)
 	return len;
 }
 
+/**
+ * bpf_get_dentry_xattr - get xattr of a dentry
+ * @dentry: dentry to get xattr from
+ * @name__str: name of the xattr
+ * @value_p: output buffer of the xattr value
+ *
+ * Get xattr *name__str* of *dentry* and store the output in *value_ptr*.
+ *
+ * For security reasons, only *name__str* with prefix "user." is allowed.
+ *
+ * Return: 0 on success, a negative value on error.
+ */
+__bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__str,
+				     struct bpf_dynptr *value_p)
+{
+	struct bpf_dynptr_kern *value_ptr = (struct bpf_dynptr_kern *)value_p;
+	struct inode *inode = d_inode(dentry);
+	u32 value_len;
+	void *value;
+	int ret;
+
+	if (WARN_ON(!inode))
+		return -EINVAL;
+
+	if (strncmp(name__str, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN))
+		return -EPERM;
+
+	value_len = __bpf_dynptr_size(value_ptr);
+	value = __bpf_dynptr_data_rw(value_ptr, value_len);
+	if (!value)
+		return -EINVAL;
+
+	ret = inode_permission(&nop_mnt_idmap, inode, MAY_READ);
+	if (ret)
+		return ret;
+	return __vfs_getxattr(dentry, inode, name__str, value, value_len);
+}
+
+/**
+ * bpf_get_file_xattr - get xattr of a file
+ * @file: file to get xattr from
+ * @name__str: name of the xattr
+ * @value_p: output buffer of the xattr value
+ *
+ * Get xattr *name__str* of *file* and store the output in *value_ptr*.
+ *
+ * For security reasons, only *name__str* with prefix "user." is allowed.
+ *
+ * Return: 0 on success, a negative value on error.
+ */
+__bpf_kfunc int bpf_get_file_xattr(struct file *file, const char *name__str,
+				   struct bpf_dynptr *value_p)
+{
+	struct dentry *dentry;
+
+	dentry = file_dentry(file);
+	return bpf_get_dentry_xattr(dentry, name__str, value_p);
+}
+
 __bpf_kfunc_end_defs();
 
 BTF_KFUNCS_START(bpf_fs_kfunc_set_ids)
@@ -99,6 +159,8 @@ BTF_ID_FLAGS(func, bpf_get_task_exe_file,
 	     KF_ACQUIRE | KF_TRUSTED_ARGS | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_put_file, KF_RELEASE)
 BTF_ID_FLAGS(func, bpf_path_d_path, KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_get_dentry_xattr, KF_SLEEPABLE | KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_get_file_xattr, KF_SLEEPABLE | KF_TRUSTED_ARGS)
 BTF_KFUNCS_END(bpf_fs_kfunc_set_ids)
 
 static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)

kernel/trace/bpf_trace.c

@@ -24,7 +24,6 @@
 #include <linux/key.h>
 #include <linux/verification.h>
 #include <linux/namei.h>
-#include <linux/fileattr.h>
 
 #include <net/bpf_sk_storage.h>
 
@@ -1439,73 +1438,6 @@ static int __init bpf_key_sig_kfuncs_init(void)
 late_initcall(bpf_key_sig_kfuncs_init);
 #endif /* CONFIG_KEYS */
 
-/* filesystem kfuncs */
-__bpf_kfunc_start_defs();
-
-/**
- * bpf_get_file_xattr - get xattr of a file
- * @file: file to get xattr from
- * @name__str: name of the xattr
- * @value_p: output buffer of the xattr value
- *
- * Get xattr *name__str* of *file* and store the output in *value_ptr*.
- *
- * For security reasons, only *name__str* with prefix "user." is allowed.
- *
- * Return: 0 on success, a negative value on error.
- */
-__bpf_kfunc int bpf_get_file_xattr(struct file *file, const char *name__str,
-				   struct bpf_dynptr *value_p)
-{
-	struct bpf_dynptr_kern *value_ptr = (struct bpf_dynptr_kern *)value_p;
-	struct dentry *dentry;
-	u32 value_len;
-	void *value;
-	int ret;
-
-	if (strncmp(name__str, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN))
-		return -EPERM;
-
-	value_len = __bpf_dynptr_size(value_ptr);
-	value = __bpf_dynptr_data_rw(value_ptr, value_len);
-	if (!value)
-		return -EINVAL;
-
-	dentry = file_dentry(file);
-	ret = inode_permission(&nop_mnt_idmap, dentry->d_inode, MAY_READ);
-	if (ret)
-		return ret;
-	return __vfs_getxattr(dentry, dentry->d_inode, name__str, value, value_len);
-}
-
-__bpf_kfunc_end_defs();
-
-BTF_KFUNCS_START(fs_kfunc_set_ids)
-BTF_ID_FLAGS(func, bpf_get_file_xattr, KF_SLEEPABLE | KF_TRUSTED_ARGS)
-BTF_KFUNCS_END(fs_kfunc_set_ids)
-
-static int bpf_get_file_xattr_filter(const struct bpf_prog *prog, u32 kfunc_id)
-{
-	if (!btf_id_set8_contains(&fs_kfunc_set_ids, kfunc_id))
-		return 0;
-
-	/* Only allow to attach from LSM hooks, to avoid recursion */
-	return prog->type != BPF_PROG_TYPE_LSM ? -EACCES : 0;
-}
-
-static const struct btf_kfunc_id_set bpf_fs_kfunc_set = {
-	.owner = THIS_MODULE,
-	.set = &fs_kfunc_set_ids,
-	.filter = bpf_get_file_xattr_filter,
-};
-
-static int __init bpf_fs_kfuncs_init(void)
-{
-	return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fs_kfunc_set);
-}
-
-late_initcall(bpf_fs_kfuncs_init);
-
 static const struct bpf_func_proto *
 bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {

tools/testing/selftests/bpf/bpf_kfuncs.h

@@ -45,7 +45,7 @@ extern int bpf_dynptr_clone(const struct bpf_dynptr *ptr, struct bpf_dynptr *clo
 
 /* Description
  *  Modify the address of a AF_UNIX sockaddr.
- * Returns__bpf_kfunc
+ * Returns
  *  -EINVAL if the address size is too big or, 0 if the sockaddr was successfully modified.
  */
 extern int bpf_sock_addr_set_sun_path(struct bpf_sock_addr_kern *sa_kern,
@@ -78,4 +78,13 @@ extern int bpf_verify_pkcs7_signature(struct bpf_dynptr *data_ptr,
 
 extern bool bpf_session_is_return(void) __ksym __weak;
 extern __u64 *bpf_session_cookie(void) __ksym __weak;
+
+struct dentry;
+/* Description
+ *  Returns xattr of a dentry
+ * Returns
+ *  Error code
+ */
+extern int bpf_get_dentry_xattr(struct dentry *dentry, const char *name,
+			      struct bpf_dynptr *value_ptr) __ksym __weak;
 #endif

tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c

@@ -16,6 +16,7 @@ static void test_xattr(void)
 {
 	struct test_get_xattr *skel = NULL;
 	int fd = -1, err;
+	int v[32];
 
 	fd = open(testfile, O_CREAT | O_RDONLY, 0644);
 	if (!ASSERT_GE(fd, 0, "create_file"))
@@ -50,7 +51,13 @@ static void test_xattr(void)
 	if (!ASSERT_GE(fd, 0, "open_file"))
 		goto out;
 
-	ASSERT_EQ(skel->bss->found_xattr, 1, "found_xattr");
+	ASSERT_EQ(skel->bss->found_xattr_from_file, 1, "found_xattr_from_file");
+
+	/* Trigger security_inode_getxattr */
+	err = getxattr(testfile, "user.kfuncs", v, sizeof(v));
+	ASSERT_EQ(err, -1, "getxattr_return");
+	ASSERT_EQ(errno, EINVAL, "getxattr_errno");
+	ASSERT_EQ(skel->bss->found_xattr_from_dentry, 1, "found_xattr_from_dentry");
 
 out:
 	close(fd);

tools/testing/selftests/bpf/progs/test_get_xattr.c

@@ -2,6 +2,7 @@
 /* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
 
 #include "vmlinux.h"
+#include <errno.h>
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 #include "bpf_kfuncs.h"
@@ -9,10 +10,12 @@
 char _license[] SEC("license") = "GPL";
 
 __u32 monitored_pid;
-__u32 found_xattr;
+__u32 found_xattr_from_file;
+__u32 found_xattr_from_dentry;
 
 static const char expected_value[] = "hello";
-char value[32];
+char value1[32];
+char value2[32];
 
 SEC("lsm.s/file_open")
 int BPF_PROG(test_file_open, struct file *f)
@@ -25,13 +28,37 @@ int BPF_PROG(test_file_open, struct file *f)
 	if (pid != monitored_pid)
 		return 0;
 
-	bpf_dynptr_from_mem(value, sizeof(value), 0, &value_ptr);
+	bpf_dynptr_from_mem(value1, sizeof(value1), 0, &value_ptr);
 
 	ret = bpf_get_file_xattr(f, "user.kfuncs", &value_ptr);
 	if (ret != sizeof(expected_value))
 		return 0;
-	if (bpf_strncmp(value, ret, expected_value))
+	if (bpf_strncmp(value1, ret, expected_value))
 		return 0;
-	found_xattr = 1;
+	found_xattr_from_file = 1;
 	return 0;
 }
+
+SEC("lsm.s/inode_getxattr")
+int BPF_PROG(test_inode_getxattr, struct dentry *dentry, char *name)
+{
+	struct bpf_dynptr value_ptr;
+	__u32 pid;
+	int ret;
+
+	pid = bpf_get_current_pid_tgid() >> 32;
+	if (pid != monitored_pid)
+		return 0;
+
+	bpf_dynptr_from_mem(value2, sizeof(value2), 0, &value_ptr);
+
+	ret = bpf_get_dentry_xattr(dentry, "user.kfuncs", &value_ptr);
+	if (ret != sizeof(expected_value))
+		return 0;
+	if (bpf_strncmp(value2, ret, expected_value))
+		return 0;
+	found_xattr_from_dentry = 1;
+
+	/* return non-zero to fail getxattr from user space */
+	return -EINVAL;
+}