From: Tadeusz Struk <tadeusz.struk@linaro.org>
To: bpf@vger.kernel.org
Cc: Tadeusz Struk <tadeusz.struk@linaro.org>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Andrii Nakryiko" <andrii@kernel.org>,
"Martin KaFai Lau" <kafai@fb.com>,
"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
"John Fastabend" <john.fastabend@gmail.com>,
"KP Singh" <kpsingh@kernel.org>,
netdev@vger.kernel.org, stable@vger.kernel.org,
linux-kernel@vger.kernel.org,
syzbot+f264bffdfbd5614f3bb2@syzkaller.appspotmail.com
Subject: [PATCH] bpf: Fix KASAN use-after-free Read in compute_effective_progs
Date: Tue, 5 Apr 2022 10:03:56 -0700 [thread overview]
Message-ID: <20220405170356.43128-1-tadeusz.struk@linaro.org> (raw)
Syzbot found a Use After Free bug in compute_effective_progs().
The reproducer creates a number of BPF links, and causes a fault
injected alloc to fail, while calling bpf_link_detach on them.
Link detach triggers the link to be freed by bpf_link_free(),
which calls __cgroup_bpf_detach() and update_effective_progs().
If the memory allocation in this function fails, the function restores
the pointer to the bpf_cgroup_link on the cgroup list, but the memory
gets freed just after it returns. After this, every subsequent call to
update_effective_progs() causes this already deallocated pointer to be
dereferenced in prog_list_length(), and triggers KASAN UAF error.
To fix this don't preserve the pointer to the link on the cgroup list
in __cgroup_bpf_detach(), but proceed with the cleanup and retry calling
update_effective_progs() again afterwards.
Cc: "Alexei Starovoitov" <ast@kernel.org>
Cc: "Daniel Borkmann" <daniel@iogearbox.net>
Cc: "Andrii Nakryiko" <andrii@kernel.org>
Cc: "Martin KaFai Lau" <kafai@fb.com>
Cc: "Song Liu" <songliubraving@fb.com>
Cc: "Yonghong Song" <yhs@fb.com>
Cc: "John Fastabend" <john.fastabend@gmail.com>
Cc: "KP Singh" <kpsingh@kernel.org>
Cc: <netdev@vger.kernel.org>
Cc: <bpf@vger.kernel.org>
Cc: <stable@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>
Link: https://syzkaller.appspot.com/bug?id=8ebf179a95c2a2670f7cf1ba62429ec044369db4
Fixes: af6eea57437a ("bpf: Implement bpf_link-based cgroup BPF program attachment")
Reported-by: <syzbot+f264bffdfbd5614f3bb2@syzkaller.appspotmail.com>
Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
---
kernel/bpf/cgroup.c | 25 ++++++++++++++-----------
1 file changed, 14 insertions(+), 11 deletions(-)
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 128028efda64..b6307337a3c7 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -723,10 +723,11 @@ static int __cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
pl->link = NULL;
err = update_effective_progs(cgrp, atype);
- if (err)
- goto cleanup;
-
- /* now can actually delete it from this cgroup list */
+ /*
+ * Proceed regardless of error. The link and/or prog will be freed
+ * just after this function returns so just delete it from this
+ * cgroup list and retry calling update_effective_progs again later.
+ */
list_del(&pl->node);
kfree(pl);
if (list_empty(progs))
@@ -735,12 +736,11 @@ static int __cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
if (old_prog)
bpf_prog_put(old_prog);
static_branch_dec(&cgroup_bpf_enabled_key[atype]);
- return 0;
-cleanup:
- /* restore back prog or link */
- pl->prog = old_prog;
- pl->link = link;
+ /* In case of error call update_effective_progs again */
+ if (err)
+ err = update_effective_progs(cgrp, atype);
+
return err;
}
@@ -881,6 +881,7 @@ static void bpf_cgroup_link_release(struct bpf_link *link)
struct bpf_cgroup_link *cg_link =
container_of(link, struct bpf_cgroup_link, link);
struct cgroup *cg;
+ int err;
/* link might have been auto-detached by dying cgroup already,
* in that case our work is done here
@@ -896,8 +897,10 @@ static void bpf_cgroup_link_release(struct bpf_link *link)
return;
}
- WARN_ON(__cgroup_bpf_detach(cg_link->cgroup, NULL, cg_link,
- cg_link->type));
+ err = __cgroup_bpf_detach(cg_link->cgroup, NULL, cg_link,
+ cg_link->type);
+ if (err)
+ pr_warn("cgroup_bpf_detach() failed, err %d\n", err);
cg = cg_link->cgroup;
cg_link->cgroup = NULL;
--
2.35.1
next reply other threads:[~2022-04-05 20:10 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-05 17:03 Tadeusz Struk [this message]
2022-04-12 14:44 ` [PATCH] bpf: Fix KASAN use-after-free Read in compute_effective_progs Tadeusz Struk
2022-04-13 4:34 ` Andrii Nakryiko
2022-04-13 17:28 ` Tadeusz Struk
2022-04-13 19:07 ` Andrii Nakryiko
2022-04-13 19:27 ` Tadeusz Struk
2022-04-13 19:49 ` Andrii Nakryiko
2022-04-15 14:13 ` [PATCH v2] " Tadeusz Struk
2022-04-20 17:07 ` Andrii Nakryiko
2022-05-13 18:38 ` Tadeusz Struk
2022-05-13 19:08 ` [PATCH v3] " Tadeusz Struk
2022-05-16 23:16 ` Andrii Nakryiko
2022-05-16 23:35 ` Tadeusz Struk
2022-05-16 23:45 ` Andrii Nakryiko
2022-05-17 18:04 ` [PATCH v4] " Tadeusz Struk
2022-05-23 21:36 ` Tadeusz Struk
2022-05-23 22:47 ` Andrii Nakryiko
2022-05-23 22:58 ` Tadeusz Struk
2022-06-02 14:37 ` Tadeusz Struk
2022-06-02 16:11 ` Andrii Nakryiko
2022-06-02 16:25 ` Tadeusz Struk
2022-06-02 16:51 ` Tadeusz Struk
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