Commit bf5c25d60861 ("skbuff: in skb_segment, call zerocopy functions once per nskb") added the call to zero copy functions in skb_segment(). The change introduced a bug in skb_segment() because skb_orphan_frags() may possibly change the number of fragments or allocate new fragments altogether leaving nrfrags and frag to point to the old values. This can cause a panic with stacktrace like the one below.
[ 193.894380] BUG: kernel NULL pointer dereference, address: 00000000000000bc [ 193.895273] CPU: 13 PID: 18164 Comm: vh-net-17428 Kdump: loaded Tainted: G O 5.15.123+ #26 [ 193.903919] RIP: 0010:skb_segment+0xb0e/0x12f0 [ 194.021892] Call Trace: [ 194.027422] <TASK> [ 194.072861] tcp_gso_segment+0x107/0x540 [ 194.082031] inet_gso_segment+0x15c/0x3d0 [ 194.090783] skb_mac_gso_segment+0x9f/0x110 [ 194.095016] __skb_gso_segment+0xc1/0x190 [ 194.103131] netem_enqueue+0x290/0xb10 [sch_netem] [ 194.107071] dev_qdisc_enqueue+0x16/0x70 [ 194.110884] __dev_queue_xmit+0x63b/0xb30 [ 194.121670] bond_start_xmit+0x159/0x380 [bonding] [ 194.128506] dev_hard_start_xmit+0xc3/0x1e0 [ 194.131787] __dev_queue_xmit+0x8a0/0xb30 [ 194.138225] macvlan_start_xmit+0x4f/0x100 [macvlan] [ 194.141477] dev_hard_start_xmit+0xc3/0x1e0 [ 194.144622] sch_direct_xmit+0xe3/0x280 [ 194.147748] __dev_queue_xmit+0x54a/0xb30 [ 194.154131] tap_get_user+0x2a8/0x9c0 [tap] [ 194.157358] tap_sendmsg+0x52/0x8e0 [tap] [ 194.167049] handle_tx_zerocopy+0x14e/0x4c0 [vhost_net] [ 194.173631] handle_tx+0xcd/0xe0 [vhost_net] [ 194.176959] vhost_worker+0x76/0xb0 [vhost] [ 194.183667] kthread+0x118/0x140 [ 194.190358] ret_from_fork+0x1f/0x30 [ 194.193670] </TASK>
In this case calling skb_orphan_frags() updated nr_frags leaving nrfrags local variable in skb_segment() stale. This resulted in the code hitting i >= nrfrags prematurely and trying to move to next frag_skb using list_skb pointer, which was NULL, and caused kernel panic. Move the call to zero copy functions before using frags and nr_frags.
Fixes: bf5c25d60861 ("skbuff: in skb_segment, call zerocopy functions once per nskb") Signed-off-by: Mohamed Khalfella mkhalfella@purestorage.com Reported-by: Amit Goyal agoyal@purestorage.com Cc: stable@vger.kernel.org --- net/core/skbuff.c | 34 ++++++++++++++++++++-------------- 1 file changed, 20 insertions(+), 14 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index a298992060e6..18a33dc2d6af 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -4354,21 +4354,20 @@ 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; 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; unsigned int offset = doffset; unsigned int tnl_hlen = skb_tnl_header_len(head_skb); unsigned int partial_segs = 0; unsigned int headroom; unsigned int len = head_skb->len; + struct sk_buff *frag_skb; + skb_frag_t *frag; __be16 proto; bool csum, sg; - int nfrags = skb_shinfo(head_skb)->nr_frags; int err = -ENOMEM; int i = 0; - int pos; + int nfrags, pos;
if ((skb_shinfo(head_skb)->gso_type & SKB_GSO_DODGY) && mss != GSO_BY_FRAGS && mss != skb_headlen(head_skb)) { @@ -4445,6 +4444,13 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, headroom = skb_headroom(head_skb); pos = skb_headlen(head_skb);
+ if (skb_orphan_frags(head_skb, GFP_ATOMIC)) + return ERR_PTR(-ENOMEM); + + nfrags = skb_shinfo(head_skb)->nr_frags; + frag = skb_shinfo(head_skb)->frags; + frag_skb = head_skb; + do { struct sk_buff *nskb; skb_frag_t *nskb_frag; @@ -4465,6 +4471,10 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, (skb_headlen(list_skb) == len || sg)) { BUG_ON(skb_headlen(list_skb) > len);
+ nskb = skb_clone(list_skb, GFP_ATOMIC); + if (unlikely(!nskb)) + goto err; + i = 0; nfrags = skb_shinfo(list_skb)->nr_frags; frag = skb_shinfo(list_skb)->frags; @@ -4483,12 +4493,8 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, frag++; }
- nskb = skb_clone(list_skb, GFP_ATOMIC); list_skb = list_skb->next;
- if (unlikely(!nskb)) - goto err; - if (unlikely(pskb_trim(nskb, len))) { kfree_skb(nskb); goto err; @@ -4564,12 +4570,16 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, skb_shinfo(nskb)->flags |= skb_shinfo(head_skb)->flags & SKBFL_SHARED_FRAG;
- if (skb_orphan_frags(frag_skb, GFP_ATOMIC) || - skb_zerocopy_clone(nskb, frag_skb, GFP_ATOMIC)) + if (skb_zerocopy_clone(nskb, list_skb, GFP_ATOMIC)) goto err;
while (pos < offset + len) { if (i >= nfrags) { + if (skb_orphan_frags(list_skb, GFP_ATOMIC) || + skb_zerocopy_clone(nskb, list_skb, + GFP_ATOMIC)) + goto err; + i = 0; nfrags = skb_shinfo(list_skb)->nr_frags; frag = skb_shinfo(list_skb)->frags; @@ -4583,10 +4593,6 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, i--; frag--; } - if (skb_orphan_frags(frag_skb, GFP_ATOMIC) || - skb_zerocopy_clone(nskb, frag_skb, - GFP_ATOMIC)) - goto err;
list_skb = list_skb->next; }
On Thu, Aug 31, 2023 at 1:28 AM Mohamed Khalfella mkhalfella@purestorage.com wrote:
Commit bf5c25d60861 ("skbuff: in skb_segment, call zerocopy functions once per nskb") added the call to zero copy functions in skb_segment(). The change introduced a bug in skb_segment() because skb_orphan_frags() may possibly change the number of fragments or allocate new fragments altogether leaving nrfrags and frag to point to the old values. This can cause a panic with stacktrace like the one below.
[ 193.894380] BUG: kernel NULL pointer dereference, address: 00000000000000bc [ 193.895273] CPU: 13 PID: 18164 Comm: vh-net-17428 Kdump: loaded Tainted: G O 5.15.123+ #26 [ 193.903919] RIP: 0010:skb_segment+0xb0e/0x12f0 [ 194.021892] Call Trace: [ 194.027422] <TASK> [ 194.072861] tcp_gso_segment+0x107/0x540 [ 194.082031] inet_gso_segment+0x15c/0x3d0 [ 194.090783] skb_mac_gso_segment+0x9f/0x110 [ 194.095016] __skb_gso_segment+0xc1/0x190 [ 194.103131] netem_enqueue+0x290/0xb10 [sch_netem] [ 194.107071] dev_qdisc_enqueue+0x16/0x70 [ 194.110884] __dev_queue_xmit+0x63b/0xb30 [ 194.121670] bond_start_xmit+0x159/0x380 [bonding] [ 194.128506] dev_hard_start_xmit+0xc3/0x1e0 [ 194.131787] __dev_queue_xmit+0x8a0/0xb30 [ 194.138225] macvlan_start_xmit+0x4f/0x100 [macvlan] [ 194.141477] dev_hard_start_xmit+0xc3/0x1e0 [ 194.144622] sch_direct_xmit+0xe3/0x280 [ 194.147748] __dev_queue_xmit+0x54a/0xb30 [ 194.154131] tap_get_user+0x2a8/0x9c0 [tap] [ 194.157358] tap_sendmsg+0x52/0x8e0 [tap] [ 194.167049] handle_tx_zerocopy+0x14e/0x4c0 [vhost_net] [ 194.173631] handle_tx+0xcd/0xe0 [vhost_net] [ 194.176959] vhost_worker+0x76/0xb0 [vhost] [ 194.183667] kthread+0x118/0x140 [ 194.190358] ret_from_fork+0x1f/0x30 [ 194.193670] </TASK>
In this case calling skb_orphan_frags() updated nr_frags leaving nrfrags local variable in skb_segment() stale. This resulted in the code hitting i >= nrfrags prematurely and trying to move to next frag_skb using list_skb pointer, which was NULL, and caused kernel panic. Move the call to zero copy functions before using frags and nr_frags.
Fixes: bf5c25d60861 ("skbuff: in skb_segment, call zerocopy functions once per nskb") Signed-off-by: Mohamed Khalfella mkhalfella@purestorage.com Reported-by: Amit Goyal agoyal@purestorage.com Cc: stable@vger.kernel.org
net/core/skbuff.c | 34 ++++++++++++++++++++-------------- 1 file changed, 20 insertions(+), 14 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index a298992060e6..18a33dc2d6af 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -4354,21 +4354,20 @@ 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; 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; unsigned int offset = doffset; unsigned int tnl_hlen = skb_tnl_header_len(head_skb); unsigned int partial_segs = 0; unsigned int headroom; unsigned int len = head_skb->len;
struct sk_buff *frag_skb;skb_frag_t *frag; __be16 proto; bool csum, sg;
int nfrags = skb_shinfo(head_skb)->nr_frags; int err = -ENOMEM; int i = 0;int pos;
int nfrags, pos; if ((skb_shinfo(head_skb)->gso_type & SKB_GSO_DODGY) && mss != GSO_BY_FRAGS && mss != skb_headlen(head_skb)) {@@ -4445,6 +4444,13 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, headroom = skb_headroom(head_skb); pos = skb_headlen(head_skb);
if (skb_orphan_frags(head_skb, GFP_ATOMIC))return ERR_PTR(-ENOMEM);nfrags = skb_shinfo(head_skb)->nr_frags;frag = skb_shinfo(head_skb)->frags;frag_skb = head_skb;do { struct sk_buff *nskb; skb_frag_t *nskb_frag;@@ -4465,6 +4471,10 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, (skb_headlen(list_skb) == len || sg)) { BUG_ON(skb_headlen(list_skb) > len);
nskb = skb_clone(list_skb, GFP_ATOMIC);if (unlikely(!nskb))goto err;
This patch is quite complex to review, so I am asking if this part was really needed ? <1> : You moved here <2> and <3>
If this is not strictly needed, please keep the code as is to ease code review...
i = 0; nfrags = skb_shinfo(list_skb)->nr_frags; frag = skb_shinfo(list_skb)->frags;@@ -4483,12 +4493,8 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, frag++; }
nskb = skb_clone(list_skb, GFP_ATOMIC);
<2>
list_skb = list_skb->next;
if (unlikely(!nskb))goto err;
<3>
if (unlikely(pskb_trim(nskb, len))) { kfree_skb(nskb); goto err;@@ -4564,12 +4570,16 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, skb_shinfo(nskb)->flags |= skb_shinfo(head_skb)->flags & SKBFL_SHARED_FRAG;
if (skb_orphan_frags(frag_skb, GFP_ATOMIC) ||skb_zerocopy_clone(nskb, frag_skb, GFP_ATOMIC))
if (skb_zerocopy_clone(nskb, list_skb, GFP_ATOMIC))
Why using list_skb here instead of frag_skb ? Again, I have to look at the whole thing to understand why you did this.
goto err; while (pos < offset + len) { if (i >= nfrags) {
if (skb_orphan_frags(list_skb, GFP_ATOMIC) ||skb_zerocopy_clone(nskb, list_skb,GFP_ATOMIC))goto err;
This part is fine.
i = 0; nfrags = skb_shinfo(list_skb)->nr_frags; frag = skb_shinfo(list_skb)->frags;@@ -4583,10 +4593,6 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, i--; frag--; }
if (skb_orphan_frags(frag_skb, GFP_ATOMIC) ||skb_zerocopy_clone(nskb, frag_skb,GFP_ATOMIC))goto err; list_skb = list_skb->next; }-- 2.17.1
Thanks.
On 2023-08-31 08:58:51 +0200, Eric Dumazet wrote:
On Thu, Aug 31, 2023 at 1:28 AM Mohamed Khalfella mkhalfella@purestorage.com wrote:
do { struct sk_buff *nskb; skb_frag_t *nskb_frag;@@ -4465,6 +4471,10 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, (skb_headlen(list_skb) == len || sg)) { BUG_ON(skb_headlen(list_skb) > len);
nskb = skb_clone(list_skb, GFP_ATOMIC);if (unlikely(!nskb))goto err;This patch is quite complex to review, so I am asking if this part was really needed ?
Unfortunately the patch is complex because I try to avoid calling skb_orphan_frags() in the middle of processing these frags. Otherwise it would be much harder to implement because as reallocated frags do not map 1:1 with existing frags as Willem mentioned.
<1> : You moved here <2> and <3>
<2> was moved here because skb_clone() calls skb_orphan_frags(). By moving this up we do not need to call skb_orphan_frags() for list_skb and we can start to use nr_frags and frags without worrying their value is going to change.
<3> was moved here because <2> was moved here. Fail fast if we can not clone list_skb.
If this is not strictly needed, please keep the code as is to ease code review...
i = 0; nfrags = skb_shinfo(list_skb)->nr_frags; frag = skb_shinfo(list_skb)->frags;@@ -4483,12 +4493,8 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, frag++; }
nskb = skb_clone(list_skb, GFP_ATOMIC);<2>
list_skb = list_skb->next;
if (unlikely(!nskb))goto err;<3>
if (unlikely(pskb_trim(nskb, len))) { kfree_skb(nskb); goto err;@@ -4564,12 +4570,16 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, skb_shinfo(nskb)->flags |= skb_shinfo(head_skb)->flags & SKBFL_SHARED_FRAG;
if (skb_orphan_frags(frag_skb, GFP_ATOMIC) ||skb_zerocopy_clone(nskb, frag_skb, GFP_ATOMIC))
if (skb_zerocopy_clone(nskb, list_skb, GFP_ATOMIC))Why using list_skb here instead of frag_skb ? Again, I have to look at the whole thing to understand why you did this.
Oops, this is a mistake. It should be frag_skb. Will fix it run the test one more time and post v3.
On Thu, Aug 31, 2023 at 9:30 AM Mohamed Khalfella mkhalfella@purestorage.com wrote:
On 2023-08-31 08:58:51 +0200, Eric Dumazet wrote:
On Thu, Aug 31, 2023 at 1:28 AM Mohamed Khalfella mkhalfella@purestorage.com wrote:
do { struct sk_buff *nskb; skb_frag_t *nskb_frag;@@ -4465,6 +4471,10 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, (skb_headlen(list_skb) == len || sg)) { BUG_ON(skb_headlen(list_skb) > len);
nskb = skb_clone(list_skb, GFP_ATOMIC);if (unlikely(!nskb))goto err;This patch is quite complex to review, so I am asking if this part was really needed ?
Unfortunately the patch is complex because I try to avoid calling skb_orphan_frags() in the middle of processing these frags. Otherwise it would be much harder to implement because as reallocated frags do not map 1:1 with existing frags as Willem mentioned.
<1> : You moved here <2> and <3>
<2> was moved here because skb_clone() calls skb_orphan_frags(). By
Oh right, I think we should amend skb_clone() documentation, it is slightly wrong.
( I will take care of this change)
moving this up we do not need to call skb_orphan_frags() for list_skb and we can start to use nr_frags and frags without worrying their value is going to change.
<3> was moved here because <2> was moved here. Fail fast if we can not clone list_skb.
If this is not strictly needed, please keep the code as is to ease code review...
i = 0; nfrags = skb_shinfo(list_skb)->nr_frags; frag = skb_shinfo(list_skb)->frags;@@ -4483,12 +4493,8 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, frag++; }
nskb = skb_clone(list_skb, GFP_ATOMIC);<2>
list_skb = list_skb->next;
if (unlikely(!nskb))goto err;<3>
if (unlikely(pskb_trim(nskb, len))) { kfree_skb(nskb); goto err;@@ -4564,12 +4570,16 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, skb_shinfo(nskb)->flags |= skb_shinfo(head_skb)->flags & SKBFL_SHARED_FRAG;
if (skb_orphan_frags(frag_skb, GFP_ATOMIC) ||skb_zerocopy_clone(nskb, frag_skb, GFP_ATOMIC))
if (skb_zerocopy_clone(nskb, list_skb, GFP_ATOMIC))Why using list_skb here instead of frag_skb ? Again, I have to look at the whole thing to understand why you did this.
Oops, this is a mistake. It should be frag_skb. Will fix it run the test one more time and post v3.
linux-stable-mirror@lists.linaro.org
-
Eric Dumazet -
Mohamed Khalfella