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 inode_init_security hook previously took the xattr array and count as two separate output parameters (struct xattr *xattrs, int *xattr_count), which BPF programs cannot write to. Pass the xattr state as a single context object (struct lsm_xattr_ctx) instead, and have bpf_init_inode_xattr() take that context directly. Update the existing in-tree callers of inode_init_security to take and forward the new lsm_xattr_ctx. Because we rely on the hook-specific ctx layout, the kfunc is restricted to lsm/inode_init_security. Restrict the xattr names that may be set via this kfunc to the bpf.* namespace. Suggested-by: Song Liu <[email protected]> Signed-off-by: David Windsor <[email protected]> --- fs/bpf_fs_kfuncs.c | 106 +++++++++++++++++++++++++++++- 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 | 7 +- security/selinux/hooks.c | 4 +- security/smack/smack_lsm.c | 13 ++-- 12 files changed, 147 insertions(+), 30 deletions(-) diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c index 9d27be058494..193accc00796 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> @@ -353,6 +354,97 @@ __bpf_kfunc int bpf_cgroup_read_xattr(struct cgroup *cgroup, const char *name__s } #endif /* CONFIG_CGROUPS */ +static int bpf_xattrs_used(const struct lsm_xattr_ctx *ctx) +{ + const size_t prefix_len = sizeof(XATTR_BPF_LSM_SUFFIX) - 1; + 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; +} + +static int __bpf_init_inode_xattr(struct lsm_xattr_ctx *xattr_ctx, + 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; + struct xattr *xattrs; + int *xattr_count; + const void *value; + u32 value_len; + + if (!xattr_ctx || !name__str) + return -EINVAL; + + xattrs = xattr_ctx->xattrs; + xattr_count = xattr_ctx->xattr_count; + if (!xattrs || !xattr_count) + return -EINVAL; + if (bpf_xattrs_used(xattr_ctx) >= 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_KERNEL); + 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(xattr_ctx); + 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_init_inode_xattr - set an xattr on a new inode from inode_init_security + * @xattr_ctx: 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_xattr_ctx *xattr_ctx, + const char *name__str, + const struct bpf_dynptr *value_p) +{ + return __bpf_init_inode_xattr(xattr_ctx, name__str, value_p); +} + __bpf_kfunc_end_defs(); BTF_KFUNCS_START(bpf_fs_kfunc_set_ids) @@ -363,13 +455,25 @@ BTF_ID_FLAGS(func, bpf_get_dentry_xattr, KF_SLEEPABLE) 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_init_inode_xattr, KF_SLEEPABLE) BTF_KFUNCS_END(bpf_fs_kfunc_set_ids) +BTF_ID_LIST(bpf_lsm_inode_init_security_btf_ids) +BTF_ID(func, bpf_lsm_inode_init_security) + +BTF_ID_LIST(bpf_init_inode_xattr_btf_ids) +BTF_ID(func, bpf_init_inode_xattr) + static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id) { if (!btf_id_set8_contains(&bpf_fs_kfunc_set_ids, kfunc_id) || - prog->type == BPF_PROG_TYPE_LSM) + prog->type == BPF_PROG_TYPE_LSM) { + /* bpf_init_inode_xattr only attaches to inode_init_security. */ + if (kfunc_id == bpf_init_inode_xattr_btf_ids[0] && + prog->aux->attach_btf_id != bpf_lsm_inode_init_security_btf_ids[0]) + return -EACCES; return 0; + } return -EACCES; } diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h index 643809cc78c3..b97a3d79529d 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 1 + struct bpf_storage_blob { struct bpf_local_storage __rcu *storage; }; diff --git a/include/linux/evm.h b/include/linux/evm.h index 913f4573b203..dff930bc10ba 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_xattr_ctx; + #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_xattr_ctx *xattr_ctx); 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_xattr_ctx *xattr_ctx) { return 0; } diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h index 2b8dfb35caed..0df364ebb0a5 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_xattr_ctx *xattr_ctx) 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..2133b729e87d 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_xattr_ctx *ctx) { - if (unlikely(!xattrs)) + if (unlikely(!ctx || !ctx->xattrs || !ctx->xattr_count)) 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 41d7367cf403..a2fc72e63ada 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_xattr_ctx { + struct xattr *xattrs; + 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/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c index c5c925f00202..fbbb4e1c04fc 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) = { diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index b59e3f121b8a..c25301f25a0a 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_xattr_ctx *xattr_ctx) { struct evm_xattr *xattr_data; struct xattr *xattr, *evm_xattr; + struct xattr *xattrs; bool evm_protected_xattrs = false; int rc; + xattrs = xattr_ctx ? xattr_ctx->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(xattr_ctx); /* * Array terminator (xattr name = NULL) must be the first non-filled * xattr slot. diff --git a/security/security.c b/security/security.c index 4e999f023651..4cd43914ce93 100644 --- a/security/security.c +++ b/security/security.c @@ -1334,6 +1334,7 @@ int security_inode_init_security(struct inode *inode, struct inode *dir, { struct lsm_static_call *scall; struct xattr *new_xattrs = NULL; + struct lsm_xattr_ctx xattr_ctx; int ret = -EOPNOTSUPP, xattr_count = 0; if (unlikely(IS_PRIVATE(inode))) @@ -1349,10 +1350,12 @@ int security_inode_init_security(struct inode *inode, struct inode *dir, if (!new_xattrs) return -ENOMEM; } + xattr_ctx.xattrs = new_xattrs; + xattr_ctx.xattr_count = &xattr_count; 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, + &xattr_ctx); if (ret && ret != -EOPNOTSUPP) goto out; /* diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 97801966bf32..dca81a22bf83 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2962,11 +2962,11 @@ 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_xattr_ctx *xattr_ctx) { const struct cred_security_struct *crsec = selinux_cred(current_cred()); struct superblock_security_struct *sbsec; - struct xattr *xattr = lsm_get_xattr_slot(xattrs, xattr_count); + struct xattr *xattr = lsm_get_xattr_slot(xattr_ctx); u32 newsid, clen; u16 newsclass; int rc; diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c index 3f9ae05039a2..ea9549c666a1 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_xattr_ctx *xattr_ctx, 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(xattr_ctx); 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) + * @xattr_ctx: 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_xattr_ctx *xattr_ctx) { struct task_smack *tsp = smack_cred(current_cred()); struct inode_smack * const issp = smack_inode(inode); @@ -1057,7 +1056,7 @@ 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, + if (xattr_dupval(xattr_ctx, XATTR_SMACK_TRANSMUTE, TRANS_TRUE, TRANS_TRUE_SIZE @@ -1067,7 +1066,7 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir, } if (rc == 0) - if (xattr_dupval(xattrs, xattr_count, + if (xattr_dupval(xattr_ctx, XATTR_SMACK_SUFFIX, issp->smk_inode->smk_known, strlen(issp->smk_inode->smk_known) -- 2.53.0
