diff mbox series

[bpf-next,v3,1/3] bpf: Pin the start cgroup in cgroup_iter_seq_init()

Message ID 20221121073440.1828292-2-houtao@huaweicloud.com (mailing list archive)
State Accepted
Commit 1a5160d4d8fe63ba4964cfff4a85831b6af75f2d
Delegated to: BPF
Headers show
Series bpf: Pin the start cgroup for cgroup iterator | expand

Checks

Context Check Description
bpf/vmtest-bpf-next-PR success PR summary
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netdev/fixes_present success Fixes tag not required for -next series
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netdev/cover_letter success Series has a cover letter
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 2 this patch: 2
netdev/cc_maintainers fail 1 blamed authors not CCed: tj@kernel.org; 1 maintainers not CCed: tj@kernel.org
netdev/build_clang success Errors and warnings before: 5 this patch: 5
netdev/module_param success Was 0 now: 0
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netdev/check_selftest success No net selftest shell script
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Commit Message

Hou Tao Nov. 21, 2022, 7:34 a.m. UTC
From: Hou Tao <houtao1@huawei.com>

bpf_iter_attach_cgroup() has already acquired an extra reference for the
start cgroup, but the reference may be released if the iterator link fd
is closed after the creation of iterator fd, and it may lead to
user-after-free problem when reading the iterator fd.

An alternative fix is pinning iterator link when opening iterator,
but it will make iterator link being still visible after the close of
iterator link fd and the behavior is different with other link types, so
just fixing it by acquiring another reference for the start cgroup.

Fixes: d4ccaf58a847 ("bpf: Introduce cgroup iter")
Signed-off-by: Hou Tao <houtao1@huawei.com>
---
 kernel/bpf/cgroup_iter.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

Comments

Yonghong Song Nov. 21, 2022, 4:27 p.m. UTC | #1
On 11/20/22 11:34 PM, Hou Tao wrote:
> From: Hou Tao <houtao1@huawei.com>
> 
> bpf_iter_attach_cgroup() has already acquired an extra reference for the
> start cgroup, but the reference may be released if the iterator link fd
> is closed after the creation of iterator fd, and it may lead to
> user-after-free problem when reading the iterator fd.
> 
> An alternative fix is pinning iterator link when opening iterator,
> but it will make iterator link being still visible after the close of
> iterator link fd and the behavior is different with other link types, so
> just fixing it by acquiring another reference for the start cgroup.
> 
> Fixes: d4ccaf58a847 ("bpf: Introduce cgroup iter")
> Signed-off-by: Hou Tao <houtao1@huawei.com>

Acked-by: Yonghong Song <yhs@fb.com>
diff mbox series

Patch

diff --git a/kernel/bpf/cgroup_iter.c b/kernel/bpf/cgroup_iter.c
index fbc6167c3599..06989d278846 100644
--- a/kernel/bpf/cgroup_iter.c
+++ b/kernel/bpf/cgroup_iter.c
@@ -164,16 +164,30 @@  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),
 };