linux/kernel/bpf/cgroup_iter.c
Chuyi Zhou 0de4f50de2 bpf: Let verifier consider {task,cgroup} is trusted in bpf_iter_reg
BTF_TYPE_SAFE_TRUSTED(struct bpf_iter__task) in verifier.c wanted to
teach BPF verifier that bpf_iter__task -> task is a trusted ptr. But it
doesn't work well.

The reason is, bpf_iter__task -> task would go through btf_ctx_access()
which enforces the reg_type of 'task' is ctx_arg_info->reg_type, and in
task_iter.c, we actually explicitly declare that the
ctx_arg_info->reg_type is PTR_TO_BTF_ID_OR_NULL.

Actually we have a previous case like this[1] where PTR_TRUSTED is added to
the arg flag for map_iter.

This patch sets ctx_arg_info->reg_type is PTR_TO_BTF_ID_OR_NULL |
PTR_TRUSTED in task_reg_info.

Similarly, bpf_cgroup_reg_info -> cgroup is also PTR_TRUSTED since we are
under the protection of cgroup_mutex and we would check cgroup_is_dead()
in __cgroup_iter_seq_show().

This patch is to improve the user experience of the newly introduced
bpf_iter_css_task kfunc before hitting the mainline. The Fixes tag is
pointing to the commit introduced the bpf_iter_css_task kfunc.

Link[1]:https://lore.kernel.org/all/20230706133932.45883-3-aspsk@isovalent.com/

Fixes: 9c66dc94b6 ("bpf: Introduce css_task open-coded iterator kfuncs")
Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20231107132204.912120-2-zhouchuyi@bytedance.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
2023-11-07 15:24:25 -08:00

360 lines
9.9 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2022 Google */
#include <linux/bpf.h>
#include <linux/btf_ids.h>
#include <linux/cgroup.h>
#include <linux/kernel.h>
#include <linux/seq_file.h>
#include "../cgroup/cgroup-internal.h" /* cgroup_mutex and cgroup_is_dead */
/* cgroup_iter provides four modes of traversal to the cgroup hierarchy.
*
* 1. Walk the descendants of a cgroup in pre-order.
* 2. Walk the descendants of a cgroup in post-order.
* 3. Walk the ancestors of a cgroup.
* 4. Show the given cgroup only.
*
* For walking descendants, cgroup_iter can walk in either pre-order or
* post-order. For walking ancestors, the iter walks up from a cgroup to
* the root.
*
* The iter program can terminate the walk early by returning 1. Walk
* continues if prog returns 0.
*
* The prog can check (seq->num == 0) to determine whether this is
* the first element. The prog may also be passed a NULL cgroup,
* which means the walk has completed and the prog has a chance to
* do post-processing, such as outputting an epilogue.
*
* Note: the iter_prog is called with cgroup_mutex held.
*
* Currently only one session is supported, which means, depending on the
* volume of data bpf program intends to send to user space, the number
* of cgroups that can be walked is limited. For example, given the current
* buffer size is 8 * PAGE_SIZE, if the program sends 64B data for each
* cgroup, assuming PAGE_SIZE is 4kb, the total number of cgroups that can
* be walked is 512. This is a limitation of cgroup_iter. If the output data
* is larger than the kernel buffer size, after all data in the kernel buffer
* is consumed by user space, the subsequent read() syscall will signal
* EOPNOTSUPP. In order to work around, the user may have to update their
* program to reduce the volume of data sent to output. For example, skip
* some uninteresting cgroups.
*/
struct bpf_iter__cgroup {
__bpf_md_ptr(struct bpf_iter_meta *, meta);
__bpf_md_ptr(struct cgroup *, cgroup);
};
struct cgroup_iter_priv {
struct cgroup_subsys_state *start_css;
bool visited_all;
bool terminate;
int order;
};
static void *cgroup_iter_seq_start(struct seq_file *seq, loff_t *pos)
{
struct cgroup_iter_priv *p = seq->private;
cgroup_lock();
/* cgroup_iter doesn't support read across multiple sessions. */
if (*pos > 0) {
if (p->visited_all)
return NULL;
/* Haven't visited all, but because cgroup_mutex has dropped,
* return -EOPNOTSUPP to indicate incomplete iteration.
*/
return ERR_PTR(-EOPNOTSUPP);
}
++*pos;
p->terminate = false;
p->visited_all = false;
if (p->order == BPF_CGROUP_ITER_DESCENDANTS_PRE)
return css_next_descendant_pre(NULL, p->start_css);
else if (p->order == BPF_CGROUP_ITER_DESCENDANTS_POST)
return css_next_descendant_post(NULL, p->start_css);
else /* BPF_CGROUP_ITER_SELF_ONLY and BPF_CGROUP_ITER_ANCESTORS_UP */
return p->start_css;
}
static int __cgroup_iter_seq_show(struct seq_file *seq,
struct cgroup_subsys_state *css, int in_stop);
static void cgroup_iter_seq_stop(struct seq_file *seq, void *v)
{
struct cgroup_iter_priv *p = seq->private;
cgroup_unlock();
/* pass NULL to the prog for post-processing */
if (!v) {
__cgroup_iter_seq_show(seq, NULL, true);
p->visited_all = true;
}
}
static void *cgroup_iter_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
struct cgroup_subsys_state *curr = (struct cgroup_subsys_state *)v;
struct cgroup_iter_priv *p = seq->private;
++*pos;
if (p->terminate)
return NULL;
if (p->order == BPF_CGROUP_ITER_DESCENDANTS_PRE)
return css_next_descendant_pre(curr, p->start_css);
else if (p->order == BPF_CGROUP_ITER_DESCENDANTS_POST)
return css_next_descendant_post(curr, p->start_css);
else if (p->order == BPF_CGROUP_ITER_ANCESTORS_UP)
return curr->parent;
else /* BPF_CGROUP_ITER_SELF_ONLY */
return NULL;
}
static int __cgroup_iter_seq_show(struct seq_file *seq,
struct cgroup_subsys_state *css, int in_stop)
{
struct cgroup_iter_priv *p = seq->private;
struct bpf_iter__cgroup ctx;
struct bpf_iter_meta meta;
struct bpf_prog *prog;
int ret = 0;
/* cgroup is dead, skip this element */
if (css && cgroup_is_dead(css->cgroup))
return 0;
ctx.meta = &meta;
ctx.cgroup = css ? css->cgroup : NULL;
meta.seq = seq;
prog = bpf_iter_get_info(&meta, in_stop);
if (prog)
ret = bpf_iter_run_prog(prog, &ctx);
/* if prog returns > 0, terminate after this element. */
if (ret != 0)
p->terminate = true;
return 0;
}
static int cgroup_iter_seq_show(struct seq_file *seq, void *v)
{
return __cgroup_iter_seq_show(seq, (struct cgroup_subsys_state *)v,
false);
}
static const struct seq_operations cgroup_iter_seq_ops = {
.start = cgroup_iter_seq_start,
.next = cgroup_iter_seq_next,
.stop = cgroup_iter_seq_stop,
.show = cgroup_iter_seq_show,
};
BTF_ID_LIST_GLOBAL_SINGLE(bpf_cgroup_btf_id, struct, cgroup)
static int cgroup_iter_seq_init(void *priv, struct bpf_iter_aux_info *aux)
{
struct cgroup_iter_priv *p = (struct cgroup_iter_priv *)priv;
struct cgroup *cgrp = aux->cgroup.start;
/* bpf_iter_attach_cgroup() has already acquired an extra reference
* for the start cgroup, but the reference may be released after
* cgroup_iter_seq_init(), so acquire another reference for the
* start cgroup.
*/
p->start_css = &cgrp->self;
css_get(p->start_css);
p->terminate = false;
p->visited_all = false;
p->order = aux->cgroup.order;
return 0;
}
static void cgroup_iter_seq_fini(void *priv)
{
struct cgroup_iter_priv *p = (struct cgroup_iter_priv *)priv;
css_put(p->start_css);
}
static const struct bpf_iter_seq_info cgroup_iter_seq_info = {
.seq_ops = &cgroup_iter_seq_ops,
.init_seq_private = cgroup_iter_seq_init,
.fini_seq_private = cgroup_iter_seq_fini,
.seq_priv_size = sizeof(struct cgroup_iter_priv),
};
static int bpf_iter_attach_cgroup(struct bpf_prog *prog,
union bpf_iter_link_info *linfo,
struct bpf_iter_aux_info *aux)
{
int fd = linfo->cgroup.cgroup_fd;
u64 id = linfo->cgroup.cgroup_id;
int order = linfo->cgroup.order;
struct cgroup *cgrp;
if (order != BPF_CGROUP_ITER_DESCENDANTS_PRE &&
order != BPF_CGROUP_ITER_DESCENDANTS_POST &&
order != BPF_CGROUP_ITER_ANCESTORS_UP &&
order != BPF_CGROUP_ITER_SELF_ONLY)
return -EINVAL;
if (fd && id)
return -EINVAL;
if (fd)
cgrp = cgroup_v1v2_get_from_fd(fd);
else if (id)
cgrp = cgroup_get_from_id(id);
else /* walk the entire hierarchy by default. */
cgrp = cgroup_get_from_path("/");
if (IS_ERR(cgrp))
return PTR_ERR(cgrp);
aux->cgroup.start = cgrp;
aux->cgroup.order = order;
return 0;
}
static void bpf_iter_detach_cgroup(struct bpf_iter_aux_info *aux)
{
cgroup_put(aux->cgroup.start);
}
static void bpf_iter_cgroup_show_fdinfo(const struct bpf_iter_aux_info *aux,
struct seq_file *seq)
{
char *buf;
buf = kzalloc(PATH_MAX, GFP_KERNEL);
if (!buf) {
seq_puts(seq, "cgroup_path:\t<unknown>\n");
goto show_order;
}
/* If cgroup_path_ns() fails, buf will be an empty string, cgroup_path
* will print nothing.
*
* Path is in the calling process's cgroup namespace.
*/
cgroup_path_ns(aux->cgroup.start, buf, PATH_MAX,
current->nsproxy->cgroup_ns);
seq_printf(seq, "cgroup_path:\t%s\n", buf);
kfree(buf);
show_order:
if (aux->cgroup.order == BPF_CGROUP_ITER_DESCENDANTS_PRE)
seq_puts(seq, "order: descendants_pre\n");
else if (aux->cgroup.order == BPF_CGROUP_ITER_DESCENDANTS_POST)
seq_puts(seq, "order: descendants_post\n");
else if (aux->cgroup.order == BPF_CGROUP_ITER_ANCESTORS_UP)
seq_puts(seq, "order: ancestors_up\n");
else /* BPF_CGROUP_ITER_SELF_ONLY */
seq_puts(seq, "order: self_only\n");
}
static int bpf_iter_cgroup_fill_link_info(const struct bpf_iter_aux_info *aux,
struct bpf_link_info *info)
{
info->iter.cgroup.order = aux->cgroup.order;
info->iter.cgroup.cgroup_id = cgroup_id(aux->cgroup.start);
return 0;
}
DEFINE_BPF_ITER_FUNC(cgroup, struct bpf_iter_meta *meta,
struct cgroup *cgroup)
static struct bpf_iter_reg bpf_cgroup_reg_info = {
.target = "cgroup",
.feature = BPF_ITER_RESCHED,
.attach_target = bpf_iter_attach_cgroup,
.detach_target = bpf_iter_detach_cgroup,
.show_fdinfo = bpf_iter_cgroup_show_fdinfo,
.fill_link_info = bpf_iter_cgroup_fill_link_info,
.ctx_arg_info_size = 1,
.ctx_arg_info = {
{ offsetof(struct bpf_iter__cgroup, cgroup),
PTR_TO_BTF_ID_OR_NULL | PTR_TRUSTED },
},
.seq_info = &cgroup_iter_seq_info,
};
static int __init bpf_cgroup_iter_init(void)
{
bpf_cgroup_reg_info.ctx_arg_info[0].btf_id = bpf_cgroup_btf_id[0];
return bpf_iter_reg_target(&bpf_cgroup_reg_info);
}
late_initcall(bpf_cgroup_iter_init);
struct bpf_iter_css {
__u64 __opaque[3];
} __attribute__((aligned(8)));
struct bpf_iter_css_kern {
struct cgroup_subsys_state *start;
struct cgroup_subsys_state *pos;
unsigned int flags;
} __attribute__((aligned(8)));
__bpf_kfunc_start_defs();
__bpf_kfunc int bpf_iter_css_new(struct bpf_iter_css *it,
struct cgroup_subsys_state *start, unsigned int flags)
{
struct bpf_iter_css_kern *kit = (void *)it;
BUILD_BUG_ON(sizeof(struct bpf_iter_css_kern) > sizeof(struct bpf_iter_css));
BUILD_BUG_ON(__alignof__(struct bpf_iter_css_kern) != __alignof__(struct bpf_iter_css));
kit->start = NULL;
switch (flags) {
case BPF_CGROUP_ITER_DESCENDANTS_PRE:
case BPF_CGROUP_ITER_DESCENDANTS_POST:
case BPF_CGROUP_ITER_ANCESTORS_UP:
break;
default:
return -EINVAL;
}
kit->start = start;
kit->pos = NULL;
kit->flags = flags;
return 0;
}
__bpf_kfunc struct cgroup_subsys_state *bpf_iter_css_next(struct bpf_iter_css *it)
{
struct bpf_iter_css_kern *kit = (void *)it;
if (!kit->start)
return NULL;
switch (kit->flags) {
case BPF_CGROUP_ITER_DESCENDANTS_PRE:
kit->pos = css_next_descendant_pre(kit->pos, kit->start);
break;
case BPF_CGROUP_ITER_DESCENDANTS_POST:
kit->pos = css_next_descendant_post(kit->pos, kit->start);
break;
case BPF_CGROUP_ITER_ANCESTORS_UP:
kit->pos = kit->pos ? kit->pos->parent : kit->start;
}
return kit->pos;
}
__bpf_kfunc void bpf_iter_css_destroy(struct bpf_iter_css *it)
{
}
__bpf_kfunc_end_defs();