* [PATCH net-next v4 0/2] net: permit skb_segment on head_frag frag_list skb
@ 2018-03-21 6:47 Yonghong Song
2018-03-21 6:47 ` [PATCH net-next v4 1/2] " Yonghong Song
2018-03-21 6:47 ` [PATCH net-next v4 2/2] net: bpf: add a test for skb_segment in test_bpf module Yonghong Song
0 siblings, 2 replies; 6+ messages in thread
From: Yonghong Song @ 2018-03-21 6:47 UTC (permalink / raw)
To: edumazet, ast, daniel, diptanu, netdev; +Cc: kernel-team
One of our in-house projects, bpf-based NAT, hits a kernel BUG_ON at
function skb_segment(), line 3667. The bpf program attaches to
clsact ingress, calls bpf_skb_change_proto to change protocol
from ipv4 to ipv6 or from ipv6 to ipv4, and then calls bpf_redirect
to send the changed packet out.
...
3665 while (pos < offset + len) {
3666 if (i >= nfrags) {
3667 BUG_ON(skb_headlen(list_skb));
...
The triggering input skb has the following properties:
list_skb = skb->frag_list;
skb->nfrags != NULL && skb_headlen(list_skb) != 0
and skb_segment() is not able to handle a frag_list skb
if its headlen (list_skb->len - list_skb->data_len) is not 0.
Patch #1 provides a simple solution to avoid BUG_ON. If
list_skb->head_frag is true, its page-backed frag will
be processed before the list_skb->frags.
Patch #2 provides a test case in test_bpf module which
constructs a skb and calls skb_segment() directly. The test
case is able to trigger the BUG_ON without Patch #1.
The patch has been tested in the following setup:
ipv6_host <-> nat_server <-> ipv4_host
where nat_server has a bpf program doing ipv4<->ipv6
translation and forwarding through clsact hook
bpf_skb_change_proto.
Changelog:
v3 -> v4:
. Remove dynamic memory allocation and use rewinding
for both index and frag to remove one branch in fast path,
from Alexander.
. Fix a bunch of issues in test_bpf skb_segment() test,
including proper way to allocate skb, proper function
argument for skb_add_rx_frag and not freeint skb, etc.,
from Eric.
v2 -> v3:
. Use starting frag index -1 (instead of 0) to
special process head_frag before other frags in the skb,
from Alexander Duyck.
v1 -> v2:
. Removed never-hit BUG_ON, spotted by Linyu Yuan.
Yonghong Song (2):
net: permit skb_segment on head_frag frag_list skb
net: bpf: add a test for skb_segment in test_bpf module
lib/test_bpf.c | 91 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
net/core/skbuff.c | 36 +++++++++++++++-------
2 files changed, 114 insertions(+), 13 deletions(-)
--
2.9.5
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH net-next v4 1/2] net: permit skb_segment on head_frag frag_list skb
2018-03-21 6:47 [PATCH net-next v4 0/2] net: permit skb_segment on head_frag frag_list skb Yonghong Song
@ 2018-03-21 6:47 ` Yonghong Song
2018-03-21 6:47 ` [PATCH net-next v4 2/2] net: bpf: add a test for skb_segment in test_bpf module Yonghong Song
1 sibling, 0 replies; 6+ messages in thread
From: Yonghong Song @ 2018-03-21 6:47 UTC (permalink / raw)
To: edumazet, ast, daniel, diptanu, netdev; +Cc: kernel-team
One of our in-house projects, bpf-based NAT, hits a kernel BUG_ON at
function skb_segment(), line 3667. The bpf program attaches to
clsact ingress, calls bpf_skb_change_proto to change protocol
from ipv4 to ipv6 or from ipv6 to ipv4, and then calls bpf_redirect
to send the changed packet out.
3472 struct sk_buff *skb_segment(struct sk_buff *head_skb,
3473 netdev_features_t features)
3474 {
3475 struct sk_buff *segs = NULL;
3476 struct sk_buff *tail = NULL;
...
3665 while (pos < offset + len) {
3666 if (i >= nfrags) {
3667 BUG_ON(skb_headlen(list_skb));
3668
3669 i = 0;
3670 nfrags = skb_shinfo(list_skb)->nr_frags;
3671 frag = skb_shinfo(list_skb)->frags;
3672 frag_skb = list_skb;
...
call stack:
...
#1 [ffff883ffef03558] __crash_kexec at ffffffff8110c525
#2 [ffff883ffef03620] crash_kexec at ffffffff8110d5cc
#3 [ffff883ffef03640] oops_end at ffffffff8101d7e7
#4 [ffff883ffef03668] die at ffffffff8101deb2
#5 [ffff883ffef03698] do_trap at ffffffff8101a700
#6 [ffff883ffef036e8] do_error_trap at ffffffff8101abfe
#7 [ffff883ffef037a0] do_invalid_op at ffffffff8101acd0
#8 [ffff883ffef037b0] invalid_op at ffffffff81a00bab
[exception RIP: skb_segment+3044]
RIP: ffffffff817e4dd4 RSP: ffff883ffef03860 RFLAGS: 00010216
RAX: 0000000000002bf6 RBX: ffff883feb7aaa00 RCX: 0000000000000011
RDX: ffff883fb87910c0 RSI: 0000000000000011 RDI: ffff883feb7ab500
RBP: ffff883ffef03928 R8: 0000000000002ce2 R9: 00000000000027da
R10: 000001ea00000000 R11: 0000000000002d82 R12: ffff883f90a1ee80
R13: ffff883fb8791120 R14: ffff883feb7abc00 R15: 0000000000002ce2
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
#9 [ffff883ffef03930] tcp_gso_segment at ffffffff818713e7
--- <IRQ stack> ---
...
The triggering input skb has the following properties:
list_skb = skb->frag_list;
skb->nfrags != NULL && skb_headlen(list_skb) != 0
and skb_segment() is not able to handle a frag_list skb
if its headlen (list_skb->len - list_skb->data_len) is not 0.
This patch addressed the issue by handling skb_headlen(list_skb) != 0
case properly if list_skb->head_frag is true, which is expected in
most cases. The head frag is processed before list_skb->frags
are processed.
Reported-by: Diptanu Gon Choudhury <diptanu@fb.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
---
net/core/skbuff.c | 36 +++++++++++++++++++++++++-----------
1 file changed, 25 insertions(+), 11 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 715c134..09f4c24 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3475,7 +3475,7 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
struct sk_buff *segs = NULL;
struct sk_buff *tail = NULL;
struct sk_buff *list_skb = skb_shinfo(head_skb)->frag_list;
- skb_frag_t *frag = skb_shinfo(head_skb)->frags;
+ skb_frag_t *frag = skb_shinfo(head_skb)->frags, head_frag;
unsigned int mss = skb_shinfo(head_skb)->gso_size;
unsigned int doffset = head_skb->data - skb_mac_header(head_skb);
struct sk_buff *frag_skb = head_skb;
@@ -3664,19 +3664,30 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
while (pos < offset + len) {
if (i >= nfrags) {
- BUG_ON(skb_headlen(list_skb));
-
i = 0;
nfrags = skb_shinfo(list_skb)->nr_frags;
frag = skb_shinfo(list_skb)->frags;
- frag_skb = list_skb;
-
- BUG_ON(!nfrags);
+ if (skb_headlen(list_skb)) {
+ struct page *page;
+
+ BUG_ON(!list_skb->head_frag);
+
+ page = virt_to_head_page(list_skb->head);
+ head_frag.page.p = page;
+ head_frag.page_offset = list_skb->data -
+ (unsigned char *)page_address(page);
+ head_frag.size = skb_headlen(list_skb);
+ /* to make room for head_frag. */
+ i--; frag--;
+ }
+ if (nfrags) {
+ frag_skb = list_skb;
- if (skb_orphan_frags(frag_skb, GFP_ATOMIC) ||
- skb_zerocopy_clone(nskb, frag_skb,
- GFP_ATOMIC))
- goto err;
+ if (skb_orphan_frags(frag_skb, GFP_ATOMIC) ||
+ skb_zerocopy_clone(nskb, frag_skb,
+ GFP_ATOMIC))
+ goto err;
+ }
list_skb = list_skb->next;
}
@@ -3689,7 +3700,10 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
goto err;
}
- *nskb_frag = *frag;
+ /* head_frag could be defined in previous outer do/while
+ * loop iterations.
+ */
+ *nskb_frag = (i < 0) ? head_frag : *frag;
__skb_frag_ref(nskb_frag);
size = skb_frag_size(nskb_frag);
--
2.9.5
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH net-next v4 2/2] net: bpf: add a test for skb_segment in test_bpf module
2018-03-21 6:47 [PATCH net-next v4 0/2] net: permit skb_segment on head_frag frag_list skb Yonghong Song
2018-03-21 6:47 ` [PATCH net-next v4 1/2] " Yonghong Song
@ 2018-03-21 6:47 ` Yonghong Song
2018-03-21 15:03 ` Eric Dumazet
2018-03-21 15:26 ` Eric Dumazet
1 sibling, 2 replies; 6+ messages in thread
From: Yonghong Song @ 2018-03-21 6:47 UTC (permalink / raw)
To: edumazet, ast, daniel, diptanu, netdev; +Cc: kernel-team
Without the previous commit,
"modprobe test_bpf" will have the following errors:
...
[ 98.149165] ------------[ cut here ]------------
[ 98.159362] kernel BUG at net/core/skbuff.c:3667!
[ 98.169756] invalid opcode: 0000 [#1] SMP PTI
[ 98.179370] Modules linked in:
[ 98.179371] test_bpf(+)
...
which triggers the bug the previous commit intends to fix.
The skbs are constructed to mimic what mlx5 may generate.
The packet size/header may not mimic real cases in production. But
the processing flow is similar.
Signed-off-by: Yonghong Song <yhs@fb.com>
---
lib/test_bpf.c | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 89 insertions(+), 2 deletions(-)
diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index 2efb213..086a231 100644
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -6574,6 +6574,91 @@ static bool exclude_test(int test_id)
return test_id < test_range[0] || test_id > test_range[1];
}
+static __init struct sk_buff *build_test_skb(void)
+{
+ u32 headroom = NET_SKB_PAD + NET_IP_ALIGN + ETH_HLEN;
+ struct sk_buff *skb[2];
+ struct page *page[2];
+ int i, data_size = 8;
+
+ for (i = 0; i < 2; i++) {
+ page[i] = alloc_page(GFP_KERNEL);
+ if (!page[i]) {
+ if (i == 0)
+ goto err_page0;
+ else
+ goto err_page1;
+ }
+
+ /* this will set skb[i]->head_frag */
+ skb[i] = dev_alloc_skb(headroom + data_size);
+ if (!skb[i]) {
+ if (i == 0)
+ goto err_skb0;
+ else
+ goto err_skb1;
+ }
+
+ skb_reserve(skb[i], headroom);
+ skb_put(skb[i], data_size);
+ skb[i]->protocol = htons(ETH_P_IP);
+ skb_reset_network_header(skb[i]);
+ skb_set_mac_header(skb[i], -ETH_HLEN);
+
+ skb_add_rx_frag(skb[i], 0, page[i], 0, 64, 64);
+ // skb_headlen(skb[i]): 8, skb[i]->head_frag = 1
+ }
+
+ /* setup shinfo */
+ skb_shinfo(skb[0])->gso_size = 1448;
+ skb_shinfo(skb[0])->gso_type = SKB_GSO_TCPV4;
+ skb_shinfo(skb[0])->gso_type |= SKB_GSO_DODGY;
+ skb_shinfo(skb[0])->gso_segs = 0;
+ skb_shinfo(skb[0])->frag_list = skb[1];
+
+ /* adjust skb[0]'s len */
+ skb[0]->len += skb[1]->len;
+ skb[0]->data_len += skb[1]->data_len;
+ skb[0]->truesize += skb[1]->truesize;
+
+ return skb[0];
+
+err_skb1:
+ __free_page(page[1]);
+err_page1:
+ kfree_skb(skb[0]);
+err_skb0:
+ __free_page(page[0]);
+err_page0:
+ return NULL;
+}
+
+static __init int test_skb_segment(void)
+{
+ netdev_features_t features;
+ struct sk_buff *skb;
+ int ret = -1;
+
+ features = NETIF_F_SG | NETIF_F_GSO_PARTIAL | NETIF_F_IP_CSUM |
+ NETIF_F_IPV6_CSUM;
+ features |= NETIF_F_RXCSUM;
+ skb = build_test_skb();
+ if (!skb) {
+ pr_info("%s: failed to build_test_skb", __func__);
+ goto done;
+ }
+
+ if (skb_segment(skb, features)) {
+ ret = 0;
+ pr_info("%s: success in skb_segment!", __func__);
+ } else {
+ pr_info("%s: failed in skb_segment!", __func__);
+ }
+ kfree_skb(skb);
+done:
+ return ret;
+}
+
static __init int test_bpf(void)
{
int i, err_cnt = 0, pass_cnt = 0;
@@ -6632,9 +6717,11 @@ static int __init test_bpf_init(void)
return ret;
ret = test_bpf();
-
destroy_bpf_tests();
- return ret;
+ if (ret)
+ return ret;
+
+ return test_skb_segment();
}
static void __exit test_bpf_exit(void)
--
2.9.5
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH net-next v4 2/2] net: bpf: add a test for skb_segment in test_bpf module
2018-03-21 6:47 ` [PATCH net-next v4 2/2] net: bpf: add a test for skb_segment in test_bpf module Yonghong Song
@ 2018-03-21 15:03 ` Eric Dumazet
2018-03-21 15:26 ` Eric Dumazet
1 sibling, 0 replies; 6+ messages in thread
From: Eric Dumazet @ 2018-03-21 15:03 UTC (permalink / raw)
To: Yonghong Song, edumazet, ast, daniel, diptanu, netdev; +Cc: kernel-team
On 03/20/2018 11:47 PM, Yonghong Song wrote:
...
+
> +static __init int test_skb_segment(void)
> +{
> + netdev_features_t features;
> + struct sk_buff *skb;
> + int ret = -1;
> +
> + features = NETIF_F_SG | NETIF_F_GSO_PARTIAL | NETIF_F_IP_CSUM |
> + NETIF_F_IPV6_CSUM;
> + features |= NETIF_F_RXCSUM;
> + skb = build_test_skb();
> + if (!skb) {
> + pr_info("%s: failed to build_test_skb", __func__);
> + goto done;
> + }
> +
> + if (skb_segment(skb, features)) {
> + ret = 0;
> + pr_info("%s: success in skb_segment!", __func__);
> + } else {
> + pr_info("%s: failed in skb_segment!", __func__);
> + }
If skb_segmen() was successful skb was already freed.
kfree_skb(old_skb) should thus panic the box, if you run this code
on a kernel having some debugging features like KASAN
So if you do not store in a variable the return of skb_segment(),
you can not properly free memory.
> + kfree_skb(skb);
> +done:
> + return ret;
> +}
> +
>
Please make sure to fully test this code.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH net-next v4 2/2] net: bpf: add a test for skb_segment in test_bpf module
2018-03-21 6:47 ` [PATCH net-next v4 2/2] net: bpf: add a test for skb_segment in test_bpf module Yonghong Song
2018-03-21 15:03 ` Eric Dumazet
@ 2018-03-21 15:26 ` Eric Dumazet
2018-03-21 20:15 ` Yonghong Song
1 sibling, 1 reply; 6+ messages in thread
From: Eric Dumazet @ 2018-03-21 15:26 UTC (permalink / raw)
To: Yonghong Song, edumazet, ast, daniel, diptanu, netdev; +Cc: kernel-team
On 03/20/2018 11:47 PM, Yonghong Song wrote:
> +static __init int test_skb_segment(void)
> +{
> + netdev_features_t features;
> + struct sk_buff *skb;
> + int ret = -1;
> +
> + features = NETIF_F_SG | NETIF_F_GSO_PARTIAL | NETIF_F_IP_CSUM |
> + NETIF_F_IPV6_CSUM;
> + features |= NETIF_F_RXCSUM;
> + skb = build_test_skb();
> + if (!skb) {
> + pr_info("%s: failed to build_test_skb", __func__);
> + goto done;
> + }
> +
> + if (skb_segment(skb, features)) {
> + ret = 0;
> + pr_info("%s: success in skb_segment!", __func__);
> + } else {
> + pr_info("%s: failed in skb_segment!", __func__);
> + }
> + kfree_skb(skb);
If skb_segmen() was successful (original) skb was already freed.
kfree_skb(old_skb) should thus panic the box, if you run this code
on a kernel having some debugging features like KASAN
So you must store in a variable the return of skb_segment(),
to be able to free skb(s), using kfree_skb_list()
> +done:
> + return ret;
> +}
> +
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH net-next v4 2/2] net: bpf: add a test for skb_segment in test_bpf module
2018-03-21 15:26 ` Eric Dumazet
@ 2018-03-21 20:15 ` Yonghong Song
0 siblings, 0 replies; 6+ messages in thread
From: Yonghong Song @ 2018-03-21 20:15 UTC (permalink / raw)
To: Eric Dumazet, edumazet, ast, daniel, diptanu, netdev; +Cc: kernel-team
On 3/21/18 8:26 AM, Eric Dumazet wrote:
>
>
> On 03/20/2018 11:47 PM, Yonghong Song wrote:
>> +static __init int test_skb_segment(void)
>> +{
>> + netdev_features_t features;
>> + struct sk_buff *skb;
>> + int ret = -1;
>> +
>> + features = NETIF_F_SG | NETIF_F_GSO_PARTIAL | NETIF_F_IP_CSUM |
>> + NETIF_F_IPV6_CSUM;
>> + features |= NETIF_F_RXCSUM;
>> + skb = build_test_skb();
>> + if (!skb) {
>> + pr_info("%s: failed to build_test_skb", __func__);
>> + goto done;
>> + }
>> +
>> + if (skb_segment(skb, features)) {
>> + ret = 0;
>> + pr_info("%s: success in skb_segment!", __func__);
>> + } else {
>> + pr_info("%s: failed in skb_segment!", __func__);
>> + }
>> + kfree_skb(skb);
>
> If skb_segmen() was successful (original) skb was already freed.
>
> kfree_skb(old_skb) should thus panic the box, if you run this code
> on a kernel having some debugging features like KASAN
I tried with KASAN. It does not panic.
Looking at the code in net/core/dev.c: validate_xmit_skb:
static struct sk_buff *validate_xmit_skb(struct sk_buff *skb, struct
net_device *dev, bool *again)
...
if (netif_needs_gso(skb, features)) {
struct sk_buff *segs;
segs = skb_gso_segment(skb, features);
if (IS_ERR(segs)) {
goto out_kfree_skb;
} else if (segs) {
consume_skb(skb);
skb = segs;
}
...
out_kfree_skb:
kfree_skb(skb);
which also indicates kfree_skb/consume_skb probably is the right way
to free skb after skb_gso_segment/skb_segment.
This probably explains why my above kfree_skb(skb) does not crash.
>
> So you must store in a variable the return of skb_segment(),
> to be able to free skb(s), using kfree_skb_list()
Totally agree. Will make the change. Thanks!
>
>
>> +done:
>> + return ret;
>> +}
>> +
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2018-03-21 20:15 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-03-21 6:47 [PATCH net-next v4 0/2] net: permit skb_segment on head_frag frag_list skb Yonghong Song
2018-03-21 6:47 ` [PATCH net-next v4 1/2] " Yonghong Song
2018-03-21 6:47 ` [PATCH net-next v4 2/2] net: bpf: add a test for skb_segment in test_bpf module Yonghong Song
2018-03-21 15:03 ` Eric Dumazet
2018-03-21 15:26 ` Eric Dumazet
2018-03-21 20:15 ` Yonghong Song
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