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bpf: Support replacing cgroup-bpf program in MULTI mode

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The common use-case in production is to have multiple cgroup-bpf
programs per attach type that cover multiple use-cases. Such programs
are attached with BPF_F_ALLOW_MULTI and can be maintained by different
people.

Order of programs usually matters, for example imagine two egress
programs: the first one drops packets and the second one counts packets.
If they're swapped the result of counting program will be different.

It brings operational challenges with updating cgroup-bpf program(s)
attached with BPF_F_ALLOW_MULTI since there is no way to replace a
program:

* One way to update is to detach all programs first and then attach the
  new version(s) again in the right order. This introduces an
  interruption in the work a program is doing and may not be acceptable
  (e.g. if it's egress firewall);

* Another way is attach the new version of a program first and only then
  detach the old version. This introduces the time interval when two
  versions of same program are working, what may not be acceptable if a
  program is not idempotent. It also imposes additional burden on
  program developers to make sure that two versions of their program can
  co-exist.

Solve the problem by introducing a "replace" mode in BPF_PROG_ATTACH
command for cgroup-bpf programs being attached with BPF_F_ALLOW_MULTI
flag. This mode is enabled by newly introduced BPF_F_REPLACE attach flag
and bpf_attr.replace_bpf_fd attribute to pass fd of the old program to
replace

That way user can replace any program among those attached with
BPF_F_ALLOW_MULTI flag without the problems described above.

Details of the new API:

* If BPF_F_REPLACE is set but replace_bpf_fd doesn't have valid
  descriptor of BPF program, BPF_PROG_ATTACH will return corresponding
  error (EINVAL or EBADF).

* If replace_bpf_fd has valid descriptor of BPF program but such a
  program is not attached to specified cgroup, BPF_PROG_ATTACH will
  return ENOENT.

BPF_F_REPLACE is introduced to make the user intent clear, since
replace_bpf_fd alone can't be used for this (its default value, 0, is a
valid fd). BPF_F_REPLACE also makes it possible to extend the API in the
future (e.g. add BPF_F_BEFORE and BPF_F_AFTER if needed).

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Andrii Narkyiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/30cd850044a0057bdfcaaf154b7d2f39850ba813.1576741281.git.rdna@fb.com
This commit is contained in:
Andrey Ignatov 2019-12-18 23:44:35 -08:00 committed by Alexei Starovoitov
parent 9fab329d6a
commit 7dd68b3279
6 changed files with 54 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/linux/bpf-cgroup.h
View File

@ -85,6 +85,7 @@ int cgroup_bpf_inherit(struct cgroup *cgrp);
void cgroup_bpf_offline(struct cgroup *cgrp);
int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
struct bpf_prog *replace_prog,
enum bpf_attach_type type, u32 flags);
int __cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
enum bpf_attach_type type);
@ -93,7 +94,8 @@ int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
/* Wrapper for __cgroup_bpf_*() protected by cgroup_mutex */
int cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
enum bpf_attach_type type, u32 flags);
struct bpf_prog *replace_prog, enum bpf_attach_type type,
u32 flags);
int cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
enum bpf_attach_type type, u32 flags);
int cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,

10
include/uapi/linux/bpf.h
View File

@ -231,6 +231,11 @@ enum bpf_attach_type {
* When children program makes decision (like picking TCP CA or sock bind)
* parent program has a chance to override it.
*
* With BPF_F_ALLOW_MULTI a new program is added to the end of the list of
* programs for a cgroup. Though it's possible to replace an old program at
* any position by also specifying BPF_F_REPLACE flag and position itself in
* replace_bpf_fd attribute. Old program at this position will be released.
*
* A cgroup with MULTI or OVERRIDE flag allows any attach flags in sub-cgroups.
* A cgroup with NONE doesn't allow any programs in sub-cgroups.
* Ex1:
@ -249,6 +254,7 @@ enum bpf_attach_type {
*/
#define BPF_F_ALLOW_OVERRIDE (1U << 0)
#define BPF_F_ALLOW_MULTI (1U << 1)
#define BPF_F_REPLACE (1U << 2)
/* If BPF_F_STRICT_ALIGNMENT is used in BPF_PROG_LOAD command, the
* verifier will perform strict alignment checking as if the kernel
@ -442,6 +448,10 @@ union bpf_attr {
__u32 attach_bpf_fd; /* eBPF program to attach */
__u32 attach_type;
__u32 attach_flags;
__u32 replace_bpf_fd; /* previously attached eBPF
* program to replace if
* BPF_F_REPLACE is used
*/
};
struct { /* anonymous struct used by BPF_PROG_TEST_RUN command */

30
kernel/bpf/cgroup.c
View File

@ -282,14 +282,17 @@ cleanup:
* propagate the change to descendants
* @cgrp: The cgroup which descendants to traverse
* @prog: A program to attach
* @replace_prog: Previously attached program to replace if BPF_F_REPLACE is set
* @type: Type of attach operation
* @flags: Option flags
*
* Must be called with cgroup_mutex held.
*/
int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
struct bpf_prog *replace_prog,
enum bpf_attach_type type, u32 flags)
{
u32 saved_flags = (flags & (BPF_F_ALLOW_OVERRIDE | BPF_F_ALLOW_MULTI));
struct list_head *progs = &cgrp->bpf.progs[type];
struct bpf_prog *old_prog = NULL;
struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE],
@ -298,14 +301,15 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
enum bpf_cgroup_storage_type stype;
int err;
if ((flags & BPF_F_ALLOW_OVERRIDE) && (flags & BPF_F_ALLOW_MULTI))
if (((flags & BPF_F_ALLOW_OVERRIDE) && (flags & BPF_F_ALLOW_MULTI)) ||
((flags & BPF_F_REPLACE) && !(flags & BPF_F_ALLOW_MULTI)))
/* invalid combination */
return -EINVAL;
if (!hierarchy_allows_attach(cgrp, type))
return -EPERM;
if (!list_empty(progs) && cgrp->bpf.flags[type] != flags)
if (!list_empty(progs) && cgrp->bpf.flags[type] != saved_flags)
/* Disallow attaching non-overridable on top
* of existing overridable in this cgroup.
* Disallow attaching multi-prog if overridable or none
@ -320,7 +324,12 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
if (pl->prog == prog)
/* disallow attaching the same prog twice */
return -EINVAL;
if (pl->prog == replace_prog)
replace_pl = pl;
}
if ((flags & BPF_F_REPLACE) && !replace_pl)
/* prog to replace not found for cgroup */
return -ENOENT;
} else if (!list_empty(progs)) {
replace_pl = list_first_entry(progs, typeof(*pl), node);
}
@ -356,7 +365,7 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
for_each_cgroup_storage_type(stype)
pl->storage[stype] = storage[stype];
cgrp->bpf.flags[type] = flags;
cgrp->bpf.flags[type] = saved_flags;
err = update_effective_progs(cgrp, type);
if (err)
@ -522,6 +531,7 @@ int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
int cgroup_bpf_prog_attach(const union bpf_attr *attr,
enum bpf_prog_type ptype, struct bpf_prog *prog)
{
struct bpf_prog *replace_prog = NULL;
struct cgroup *cgrp;
int ret;
@ -529,8 +539,20 @@ int cgroup_bpf_prog_attach(const union bpf_attr *attr,
if (IS_ERR(cgrp))
return PTR_ERR(cgrp);
ret = cgroup_bpf_attach(cgrp, prog, attr->attach_type,
if ((attr->attach_flags & BPF_F_ALLOW_MULTI) &&
(attr->attach_flags & BPF_F_REPLACE)) {
replace_prog = bpf_prog_get_type(attr->replace_bpf_fd, ptype);
if (IS_ERR(replace_prog)) {
cgroup_put(cgrp);
return PTR_ERR(replace_prog);
}
}
ret = cgroup_bpf_attach(cgrp, prog, replace_prog, attr->attach_type,
attr->attach_flags);
if (replace_prog)
bpf_prog_put(replace_prog);
cgroup_put(cgrp);
return ret;
}

4
kernel/bpf/syscall.c
View File

@ -2073,10 +2073,10 @@ static int bpf_prog_attach_check_attach_type(const struct bpf_prog *prog,
}
}
#define BPF_PROG_ATTACH_LAST_FIELD attach_flags
#define BPF_PROG_ATTACH_LAST_FIELD replace_bpf_fd
#define BPF_F_ATTACH_MASK \
(BPF_F_ALLOW_OVERRIDE | BPF_F_ALLOW_MULTI)
(BPF_F_ALLOW_OVERRIDE | BPF_F_ALLOW_MULTI | BPF_F_REPLACE)
static int bpf_prog_attach(const union bpf_attr *attr)
{

5
kernel/cgroup/cgroup.c
View File

@ -6288,12 +6288,13 @@ void cgroup_sk_free(struct sock_cgroup_data *skcd)
#ifdef CONFIG_CGROUP_BPF
int cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
enum bpf_attach_type type, u32 flags)
struct bpf_prog *replace_prog, enum bpf_attach_type type,
u32 flags)
{
int ret;
mutex_lock(&cgroup_mutex);
ret = __cgroup_bpf_attach(cgrp, prog, type, flags);
ret = __cgroup_bpf_attach(cgrp, prog, replace_prog, type, flags);
mutex_unlock(&cgroup_mutex);
return ret;
}

10
tools/include/uapi/linux/bpf.h
View File

@ -231,6 +231,11 @@ enum bpf_attach_type {
* When children program makes decision (like picking TCP CA or sock bind)
* parent program has a chance to override it.
*
* With BPF_F_ALLOW_MULTI a new program is added to the end of the list of
* programs for a cgroup. Though it's possible to replace an old program at
* any position by also specifying BPF_F_REPLACE flag and position itself in
* replace_bpf_fd attribute. Old program at this position will be released.
*
* A cgroup with MULTI or OVERRIDE flag allows any attach flags in sub-cgroups.
* A cgroup with NONE doesn't allow any programs in sub-cgroups.
* Ex1:
@ -249,6 +254,7 @@ enum bpf_attach_type {
*/
#define BPF_F_ALLOW_OVERRIDE (1U << 0)
#define BPF_F_ALLOW_MULTI (1U << 1)
#define BPF_F_REPLACE (1U << 2)
/* If BPF_F_STRICT_ALIGNMENT is used in BPF_PROG_LOAD command, the
* verifier will perform strict alignment checking as if the kernel
@ -442,6 +448,10 @@ union bpf_attr {
__u32 attach_bpf_fd; /* eBPF program to attach */
__u32 attach_type;
__u32 attach_flags;
__u32 replace_bpf_fd; /* previously attached eBPF
* program to replace if
* BPF_F_REPLACE is used
*/
};
struct { /* anonymous struct used by BPF_PROG_TEST_RUN command */