Commit f63ea3e0 authored by Alexei Starovoitov's avatar Alexei Starovoitov
Browse files

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: default avatarAlexei Starovoitov <ast@kernel.org>
parents 6e083ab0 8681156c

fs/bpf_fs_kfuncs.c

+62 −0
Original line number Diff line number Diff line
@@ -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

+0 −68
Original line number Diff line number Diff line
@@ -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

+10 −1
Original line number Diff line number Diff line
@@ -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

+8 −1
Original line number Diff line number Diff line
@@ -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

+32 −5
Original line number Diff line number Diff line
@@ -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;

}