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Message-ID: <20250407142234.47591-4-jiayuan.chen@linux.dev>
Date: Mon, 7 Apr 2025 22:21:22 +0800
From: Jiayuan Chen <jiayuan.chen@...ux.dev>
To: bpf@...r.kernel.org
Cc: mrpre@....com,
Jiayuan Chen <jiayuan.chen@...ux.dev>,
John Fastabend <john.fastabend@...il.com>,
Jakub Sitnicki <jakub@...udflare.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Simon Horman <horms@...nel.org>,
Andrii Nakryiko <andrii@...nel.org>,
Eduard Zingerman <eddyz87@...il.com>,
Mykola Lysenko <mykolal@...com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>,
KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...ichev.me>,
Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>,
Shuah Khan <shuah@...nel.org>,
linux-kernel@...r.kernel.org,
netdev@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: [PATCH bpf-next v1 3/4] bpf, sockmap: Fix panic when calling skb_linearize
The panic can be reproduced by executing the command:
./bench sockmap -c 2 -p 1 -a --rx-verdict-ingress --rx-strp 100000
Then a kernel panic was captured:
'''
[ 657.460555] kernel BUG at net/core/skbuff.c:2178!
[ 657.462680] Tainted: [W]=WARN
[ 657.463287] Workqueue: events sk_psock_backlog
...
[ 657.469610] <TASK>
[ 657.469738] ? die+0x36/0x90
[ 657.469916] ? do_trap+0x1d0/0x270
[ 657.470118] ? pskb_expand_head+0x612/0xf40
[ 657.470376] ? pskb_expand_head+0x612/0xf40
[ 657.470620] ? do_error_trap+0xa3/0x170
[ 657.470846] ? pskb_expand_head+0x612/0xf40
[ 657.471092] ? handle_invalid_op+0x2c/0x40
[ 657.471335] ? pskb_expand_head+0x612/0xf40
[ 657.471579] ? exc_invalid_op+0x2d/0x40
[ 657.471805] ? asm_exc_invalid_op+0x1a/0x20
[ 657.472052] ? pskb_expand_head+0xd1/0xf40
[ 657.472292] ? pskb_expand_head+0x612/0xf40
[ 657.472540] ? lock_acquire+0x18f/0x4e0
[ 657.472766] ? find_held_lock+0x2d/0x110
[ 657.472999] ? __pfx_pskb_expand_head+0x10/0x10
[ 657.473263] ? __kmalloc_cache_noprof+0x5b/0x470
[ 657.473537] ? __pfx___lock_release.isra.0+0x10/0x10
[ 657.473826] __pskb_pull_tail+0xfd/0x1d20
[ 657.474062] ? __kasan_slab_alloc+0x4e/0x90
[ 657.474707] sk_psock_skb_ingress_enqueue+0x3bf/0x510
[ 657.475392] ? __kasan_kmalloc+0xaa/0xb0
[ 657.476010] sk_psock_backlog+0x5cf/0xd70
[ 657.476637] process_one_work+0x858/0x1a20
'''
The panic originates from the assertion BUG_ON(skb_shared(skb)) in
skb_linearize(). A previous commit(see Fixes tag) introduced skb_get()
to avoid race conditions between skb operations in the backlog and skb
release in the recvmsg path. However, this caused the panic to always
occur when skb_linearize is executed.
The "--rx-strp 100000" parameter forces the RX path to use the strparser
module which aggregates data until it reaches 100KB before calling sockmap
logic. The 100KB payload exceeds MAX_MSG_FRAGS, triggering skb_linearize.
To fix this issue, just move skb_get into sk_psock_skb_ingress_enqueue.
'''
sk_psock_backlog:
sk_psock_handle_skb
skb_get(skb) <== we move it into 'sk_psock_skb_ingress_enqueue'
sk_psock_skb_ingress____________
↓
|
| → sk_psock_skb_ingress_self
| sk_psock_skb_ingress_enqueue
sk_psock_verdict_apply_________________↑ skb_linearize
'''
Note that for verdict_apply path, the skb_get operation is unnecessary so
we add 'take_ref' param to control it's behavior.
Fixes: a454d84ee20b ("bpf, sockmap: Fix skb refcnt race after locking changes")
Signed-off-by: Jiayuan Chen <jiayuan.chen@...ux.dev>
---
net/core/skmsg.c | 31 ++++++++++++++++---------------
1 file changed, 16 insertions(+), 15 deletions(-)
diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index 9533b3e40ad7..276934673066 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -530,16 +530,22 @@ static int sk_psock_skb_ingress_enqueue(struct sk_buff *skb,
u32 off, u32 len,
struct sk_psock *psock,
struct sock *sk,
- struct sk_msg *msg)
+ struct sk_msg *msg,
+ bool take_ref)
{
int num_sge, copied;
+ /* skb_to_sgvec will fail when the total number of fragments in
+ * frag_list and frags exceeds MAX_MSG_FRAGS. For example, the
+ * caller may aggregate multiple skbs.
+ */
num_sge = skb_to_sgvec(skb, msg->sg.data, off, len);
if (num_sge < 0) {
/* skb linearize may fail with ENOMEM, but lets simply try again
* later if this happens. Under memory pressure we don't want to
* drop the skb. We need to linearize the skb so that the mapping
* in skb_to_sgvec can not error.
+ * Note that skb_linearize requires the skb not to be shared.
*/
if (skb_linearize(skb))
return -EAGAIN;
@@ -556,7 +562,7 @@ static int sk_psock_skb_ingress_enqueue(struct sk_buff *skb,
msg->sg.start = 0;
msg->sg.size = copied;
msg->sg.end = num_sge;
- msg->skb = skb;
+ msg->skb = take_ref ? skb_get(skb) : skb;
sk_psock_queue_msg(psock, msg);
sk_psock_data_ready(sk, psock);
@@ -564,7 +570,7 @@ static int sk_psock_skb_ingress_enqueue(struct sk_buff *skb,
}
static int sk_psock_skb_ingress_self(struct sk_psock *psock, struct sk_buff *skb,
- u32 off, u32 len);
+ u32 off, u32 len, bool take_ref);
static int sk_psock_skb_ingress(struct sk_psock *psock, struct sk_buff *skb,
u32 off, u32 len)
@@ -578,7 +584,7 @@ static int sk_psock_skb_ingress(struct sk_psock *psock, struct sk_buff *skb,
* correctly.
*/
if (unlikely(skb->sk == sk))
- return sk_psock_skb_ingress_self(psock, skb, off, len);
+ return sk_psock_skb_ingress_self(psock, skb, off, len, true);
msg = sk_psock_create_ingress_msg(sk, skb);
if (!msg)
return -EAGAIN;
@@ -590,7 +596,7 @@ static int sk_psock_skb_ingress(struct sk_psock *psock, struct sk_buff *skb,
* into user buffers.
*/
skb_set_owner_r(skb, sk);
- err = sk_psock_skb_ingress_enqueue(skb, off, len, psock, sk, msg);
+ err = sk_psock_skb_ingress_enqueue(skb, off, len, psock, sk, msg, true);
if (err < 0)
kfree(msg);
return err;
@@ -601,7 +607,7 @@ static int sk_psock_skb_ingress(struct sk_psock *psock, struct sk_buff *skb,
* because the skb is already accounted for here.
*/
static int sk_psock_skb_ingress_self(struct sk_psock *psock, struct sk_buff *skb,
- u32 off, u32 len)
+ u32 off, u32 len, bool take_ref)
{
struct sk_msg *msg = alloc_sk_msg(GFP_ATOMIC);
struct sock *sk = psock->sk;
@@ -610,7 +616,7 @@ static int sk_psock_skb_ingress_self(struct sk_psock *psock, struct sk_buff *skb
if (unlikely(!msg))
return -EAGAIN;
skb_set_owner_r(skb, sk);
- err = sk_psock_skb_ingress_enqueue(skb, off, len, psock, sk, msg);
+ err = sk_psock_skb_ingress_enqueue(skb, off, len, psock, sk, msg, take_ref);
if (err < 0)
kfree(msg);
return err;
@@ -619,18 +625,13 @@ static int sk_psock_skb_ingress_self(struct sk_psock *psock, struct sk_buff *skb
static int sk_psock_handle_skb(struct sk_psock *psock, struct sk_buff *skb,
u32 off, u32 len, bool ingress)
{
- int err = 0;
-
if (!ingress) {
if (!sock_writeable(psock->sk))
return -EAGAIN;
return skb_send_sock(psock->sk, skb, off, len);
}
- skb_get(skb);
- err = sk_psock_skb_ingress(psock, skb, off, len);
- if (err < 0)
- kfree_skb(skb);
- return err;
+
+ return sk_psock_skb_ingress(psock, skb, off, len);
}
static void sk_psock_skb_state(struct sk_psock *psock,
@@ -1019,7 +1020,7 @@ static int sk_psock_verdict_apply(struct sk_psock *psock, struct sk_buff *skb,
off = stm->offset;
len = stm->full_len;
}
- err = sk_psock_skb_ingress_self(psock, skb, off, len);
+ err = sk_psock_skb_ingress_self(psock, skb, off, len, false);
}
if (err < 0) {
spin_lock_bh(&psock->ingress_lock);
--
2.47.1
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