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authorYonghong Song <yhs@fb.com>2021-08-10 16:05:37 -0700
committerAndrii Nakryiko <andrii@kernel.org>2021-08-11 11:45:43 -0700
commit2d3a1e3615c5449a4583010f41a6f824a4ffa03e (patch)
treecfa5593208ffc12abd78ebc784b5bb6c080a3b92 /kernel
parent519133debcc19f5c834e7e28480b60bdc234fe02 (diff)
bpf: Add rcu_read_lock in bpf_get_current_[ancestor_]cgroup_id() helpers
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/ Fixes: 95b861a7935b ("bpf: Allow bpf_get_current_ancestor_cgroup_id for tracing") Reported-by: syzbot+7ee5c2c09c284495371f@syzkaller.appspotmail.com Signed-off-by: Yonghong Song <yhs@fb.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20210810230537.2864668-1-yhs@fb.com
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/helpers.c22
1 files changed, 16 insertions, 6 deletions
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 = {