* [PATCH bpf v4] bpf: add rcu read_lock in bpf_get_current_[ancestor_]cgroup_id() helpers
@ 2021-08-10 23:05 Yonghong Song
2021-08-11 18:46 ` Andrii Nakryiko
0 siblings, 1 reply; 2+ messages in thread
From: Yonghong Song @ 2021-08-10 23:05 UTC (permalink / raw)
To: bpf
Cc: Alexei Starovoitov, Andrii Nakryiko, Daniel Borkmann,
kernel-team, syzbot+7ee5c2c09c284495371f
Currently, if bpf_get_current_cgroup_id() or
bpf_get_current_ancestor_cgroup_id() helper is
called with sleepable programs e.g., sleepable
fentry/fmod_ret/fexit/lsm programs, a rcu warning
may appear. For example, if I added the following
hack to test_progs/test_lsm sleepable fentry program
test_sys_setdomainname:
--- a/tools/testing/selftests/bpf/progs/lsm.c
+++ b/tools/testing/selftests/bpf/progs/lsm.c
@@ -168,6 +168,10 @@ int BPF_PROG(test_sys_setdomainname, struct pt_regs *regs)
int buf = 0;
long ret;
+ __u64 cg_id = bpf_get_current_cgroup_id();
+ if (cg_id == 1000)
+ copy_test++;
+
ret = bpf_copy_from_user(&buf, sizeof(buf), ptr);
if (len == -2 && ret == 0 && buf == 1234)
copy_test++;
I will hit the following rcu warning:
include/linux/cgroup.h:481 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
1 lock held by test_progs/260:
#0: ffffffffa5173360 (rcu_read_lock_trace){....}-{0:0}, at: __bpf_prog_enter_sleepable+0x0/0xa0
stack backtrace:
CPU: 1 PID: 260 Comm: test_progs Tainted: G O 5.14.0-rc2+ #176
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
Call Trace:
dump_stack_lvl+0x56/0x7b
bpf_get_current_cgroup_id+0x9c/0xb1
bpf_prog_a29888d1c6706e09_test_sys_setdomainname+0x3e/0x89c
bpf_trampoline_6442469132_0+0x2d/0x1000
__x64_sys_setdomainname+0x5/0x110
do_syscall_64+0x3a/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xae
I can get similar warning using bpf_get_current_ancestor_cgroup_id() helper.
syzbot reported a similar issue in [1] for syscall program. Helper
bpf_get_current_cgroup_id() or bpf_get_current_ancestor_cgroup_id()
has the following callchain:
task_dfl_cgroup
task_css_set
task_css_set_check
and we have
#define task_css_set_check(task, __c) \
rcu_dereference_check((task)->cgroups, \
lockdep_is_held(&cgroup_mutex) || \
lockdep_is_held(&css_set_lock) || \
((task)->flags & PF_EXITING) || (__c))
Since cgroup_mutex/css_set_lock is not held and the task
is not existing and rcu read_lock is not held, a warning
will be issued. Note that bpf sleepable program is protected by
rcu_read_lock_trace().
The above sleepable bpf programs are already protected
by migrate_disable(). Adding rcu_read_lock() in these
two helpers will silence the above warning.
I marked the patch fixing 95b861a7935b
("bpf: Allow bpf_get_current_ancestor_cgroup_id for tracing")
which added bpf_get_current_ancestor_cgroup_id() to tracing programs
in 5.14. I think backporting 5.14 is probably good enough as sleepable
progrems are not widely used.
This patch should fix [1] as well since syscall program is a sleepable
program protected with migrate_disable().
[1] https://lore.kernel.org/bpf/0000000000006d5cab05c7d9bb87@google.com/
Reported-by: syzbot+7ee5c2c09c284495371f@syzkaller.appspotmail.com
Fixes: 95b861a7935b ("bpf: Allow bpf_get_current_ancestor_cgroup_id for tracing")
Signed-off-by: Yonghong Song <yhs@fb.com>
---
kernel/bpf/helpers.c | 22 ++++++++++++++++------
1 file changed, 16 insertions(+), 6 deletions(-)
Changelog:
v3 -> v4:
- ensure rcu_read_lock() region enclosing all accesses to cgroup.
v2 -> v3:
- use rcu_read_lock() protection for
bpf_get_current_[ancestor_]cgroup_id() helper.
v1 -> v2:
- disallow bpf_get_current_[ancestor_]cgroup_id() helper.
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 7a97b2f4747d..55f83ea09dae 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -353,9 +353,15 @@ const struct bpf_func_proto bpf_jiffies64_proto = {
#ifdef CONFIG_CGROUPS
BPF_CALL_0(bpf_get_current_cgroup_id)
{
- struct cgroup *cgrp = task_dfl_cgroup(current);
+ struct cgroup *cgrp;
+ u64 cgrp_id;
- return cgroup_id(cgrp);
+ rcu_read_lock();
+ cgrp = task_dfl_cgroup(current);
+ cgrp_id = cgroup_id(cgrp);
+ rcu_read_unlock();
+
+ return cgrp_id;
}
const struct bpf_func_proto bpf_get_current_cgroup_id_proto = {
@@ -366,13 +372,17 @@ const struct bpf_func_proto bpf_get_current_cgroup_id_proto = {
BPF_CALL_1(bpf_get_current_ancestor_cgroup_id, int, ancestor_level)
{
- struct cgroup *cgrp = task_dfl_cgroup(current);
+ struct cgroup *cgrp;
struct cgroup *ancestor;
+ u64 cgrp_id;
+ rcu_read_lock();
+ cgrp = task_dfl_cgroup(current);
ancestor = cgroup_ancestor(cgrp, ancestor_level);
- if (!ancestor)
- return 0;
- return cgroup_id(ancestor);
+ cgrp_id = ancestor ? cgroup_id(ancestor) : 0;
+ rcu_read_unlock();
+
+ return cgrp_id;
}
const struct bpf_func_proto bpf_get_current_ancestor_cgroup_id_proto = {
--
2.30.2
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH bpf v4] bpf: add rcu read_lock in bpf_get_current_[ancestor_]cgroup_id() helpers
2021-08-10 23:05 [PATCH bpf v4] bpf: add rcu read_lock in bpf_get_current_[ancestor_]cgroup_id() helpers Yonghong Song
@ 2021-08-11 18:46 ` Andrii Nakryiko
0 siblings, 0 replies; 2+ messages in thread
From: Andrii Nakryiko @ 2021-08-11 18:46 UTC (permalink / raw)
To: Yonghong Song
Cc: bpf, Alexei Starovoitov, Andrii Nakryiko, Daniel Borkmann,
Kernel Team, syzbot+7ee5c2c09c284495371f
On Tue, Aug 10, 2021 at 4:05 PM Yonghong Song <yhs@fb.com> wrote:
>
> Currently, if bpf_get_current_cgroup_id() or
> bpf_get_current_ancestor_cgroup_id() helper is
> called with sleepable programs e.g., sleepable
> fentry/fmod_ret/fexit/lsm programs, a rcu warning
> may appear. For example, if I added the following
> hack to test_progs/test_lsm sleepable fentry program
> test_sys_setdomainname:
>
> --- a/tools/testing/selftests/bpf/progs/lsm.c
> +++ b/tools/testing/selftests/bpf/progs/lsm.c
> @@ -168,6 +168,10 @@ int BPF_PROG(test_sys_setdomainname, struct pt_regs *regs)
> int buf = 0;
> long ret;
>
> + __u64 cg_id = bpf_get_current_cgroup_id();
> + if (cg_id == 1000)
> + copy_test++;
> +
> ret = bpf_copy_from_user(&buf, sizeof(buf), ptr);
> if (len == -2 && ret == 0 && buf == 1234)
> copy_test++;
>
> I will hit the following rcu warning:
>
> include/linux/cgroup.h:481 suspicious rcu_dereference_check() usage!
> other info that might help us debug this:
> rcu_scheduler_active = 2, debug_locks = 1
> 1 lock held by test_progs/260:
> #0: ffffffffa5173360 (rcu_read_lock_trace){....}-{0:0}, at: __bpf_prog_enter_sleepable+0x0/0xa0
> stack backtrace:
> CPU: 1 PID: 260 Comm: test_progs Tainted: G O 5.14.0-rc2+ #176
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
> Call Trace:
> dump_stack_lvl+0x56/0x7b
> bpf_get_current_cgroup_id+0x9c/0xb1
> bpf_prog_a29888d1c6706e09_test_sys_setdomainname+0x3e/0x89c
> bpf_trampoline_6442469132_0+0x2d/0x1000
> __x64_sys_setdomainname+0x5/0x110
> do_syscall_64+0x3a/0x80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> I can get similar warning using bpf_get_current_ancestor_cgroup_id() helper.
> syzbot reported a similar issue in [1] for syscall program. Helper
> bpf_get_current_cgroup_id() or bpf_get_current_ancestor_cgroup_id()
> has the following callchain:
> task_dfl_cgroup
> task_css_set
> task_css_set_check
> and we have
> #define task_css_set_check(task, __c) \
> rcu_dereference_check((task)->cgroups, \
> lockdep_is_held(&cgroup_mutex) || \
> lockdep_is_held(&css_set_lock) || \
> ((task)->flags & PF_EXITING) || (__c))
> Since cgroup_mutex/css_set_lock is not held and the task
> is not existing and rcu read_lock is not held, a warning
> will be issued. Note that bpf sleepable program is protected by
> rcu_read_lock_trace().
>
> The above sleepable bpf programs are already protected
> by migrate_disable(). Adding rcu_read_lock() in these
> two helpers will silence the above warning.
> I marked the patch fixing 95b861a7935b
> ("bpf: Allow bpf_get_current_ancestor_cgroup_id for tracing")
> which added bpf_get_current_ancestor_cgroup_id() to tracing programs
> in 5.14. I think backporting 5.14 is probably good enough as sleepable
> progrems are not widely used.
>
> This patch should fix [1] as well since syscall program is a sleepable
> program protected with migrate_disable().
>
> [1] https://lore.kernel.org/bpf/0000000000006d5cab05c7d9bb87@google.com/
>
> Reported-by: syzbot+7ee5c2c09c284495371f@syzkaller.appspotmail.com
> Fixes: 95b861a7935b ("bpf: Allow bpf_get_current_ancestor_cgroup_id for tracing")
> Signed-off-by: Yonghong Song <yhs@fb.com>
> ---
> kernel/bpf/helpers.c | 22 ++++++++++++++++------
> 1 file changed, 16 insertions(+), 6 deletions(-)
>
> Changelog:
> v3 -> v4:
> - ensure rcu_read_lock() region enclosing all accesses to cgroup.
Applied to bpf, thanks!
> v2 -> v3:
> - use rcu_read_lock() protection for
> bpf_get_current_[ancestor_]cgroup_id() helper.
> v1 -> v2:
> - disallow bpf_get_current_[ancestor_]cgroup_id() helper.
>
[...]
^ permalink raw reply [flat|nested] 2+ messages in thread
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2021-08-10 23:05 [PATCH bpf v4] bpf: add rcu read_lock in bpf_get_current_[ancestor_]cgroup_id() helpers Yonghong Song
2021-08-11 18:46 ` Andrii Nakryiko
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