* [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit
@ 2023-08-01 22:07 Andrew Kanner
2023-08-01 22:07 ` [PATCH v4 2/2] net: core: remove unnecessary frame_sz check in bpf_xdp_adjust_tail() Andrew Kanner
` (2 more replies)
0 siblings, 3 replies; 11+ messages in thread
From: Andrew Kanner @ 2023-08-01 22:07 UTC (permalink / raw)
To: davem, edumazet, kuba, pabeni, jasowang, netdev, brouer, dsahern,
jbrouer, john.fastabend, linux-kernel
Cc: linux-kernel-mentees, syzbot+f817490f5bd20541b90a, Andrew Kanner
Using the syzkaller repro with reduced packet size it was discovered
that XDP_PACKET_HEADROOM is not checked in tun_can_build_skb(),
although pad may be incremented in tun_build_skb(). This may end up
with exceeding the PAGE_SIZE limit in tun_build_skb().
Fixes: 7df13219d757 ("tun: reserve extra headroom only when XDP is set")
Link: https://syzkaller.appspot.com/bug?extid=f817490f5bd20541b90a
Signed-off-by: Andrew Kanner <andrew.kanner@gmail.com>
---
Notes:
v3 -> v4:
* fall back to v1, fixing only missing XDP_PACKET_HEADROOM in pad and
removing bpf_xdp_adjust_tail() check for frame_sz.
* added rcu read lock, noted by Jason Wang <jasowang@redhat.com> in v1
* I decided to leave the packet length check in tun_can_build_skb()
instead of moving to tun_build_skb() suggested by Jason Wang
<jasowang@redhat.com>. Otherwise extra packets will be dropped
without falling back to tun_alloc_skb(). And in the discussion of v3
Jesper Dangaard Brouer <jbrouer@redhat.com> noticed that XDP is ok
with a higher order pages if it's a contiguous physical memory
allocation, so falling to tun_alloc_skb() -> do_xdp_generic() should
be ok.
v2 -> v3:
* attach the forgotten changelog
v1 -> v2:
* merged 2 patches in 1, fixing both issues: WARN_ON_ONCE with
syzkaller repro and missing XDP_PACKET_HEADROOM in pad
* changed the title and description of the execution path, suggested
by Jason Wang <jasowang@redhat.com>
* move the limit check from tun_can_build_skb() to tun_build_skb() to
remove duplication and locking issue, and also drop the packet in
case of a failed check - noted by Jason Wang <jasowang@redhat.com>
drivers/net/tun.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index d75456adc62a..a1d04bc9485f 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1582,6 +1582,9 @@ static void tun_rx_batched(struct tun_struct *tun, struct tun_file *tfile,
static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
int len, int noblock, bool zerocopy)
{
+ struct bpf_prog *xdp_prog;
+ int pad = TUN_RX_PAD;
+
if ((tun->flags & TUN_TYPE_MASK) != IFF_TAP)
return false;
@@ -1594,7 +1597,13 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
if (zerocopy)
return false;
- if (SKB_DATA_ALIGN(len + TUN_RX_PAD) +
+ rcu_read_lock();
+ xdp_prog = rcu_dereference(tun->xdp_prog);
+ if (xdp_prog)
+ pad += XDP_PACKET_HEADROOM;
+ rcu_read_unlock();
+
+ if (SKB_DATA_ALIGN(len + pad) +
SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) > PAGE_SIZE)
return false;
--
2.39.3
^ permalink raw reply related [flat|nested] 11+ messages in thread
* [PATCH v4 2/2] net: core: remove unnecessary frame_sz check in bpf_xdp_adjust_tail()
2023-08-01 22:07 [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit Andrew Kanner
@ 2023-08-01 22:07 ` Andrew Kanner
2023-08-02 13:56 ` Jesper Dangaard Brouer
2023-08-03 3:20 ` Jason Wang
2023-08-02 1:07 ` [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit David Ahern
2023-08-02 14:13 ` Jesper Dangaard Brouer
2 siblings, 2 replies; 11+ messages in thread
From: Andrew Kanner @ 2023-08-01 22:07 UTC (permalink / raw)
To: davem, edumazet, kuba, pabeni, jasowang, netdev, brouer, dsahern,
jbrouer, john.fastabend, linux-kernel
Cc: linux-kernel-mentees, syzbot+f817490f5bd20541b90a, Andrew Kanner
Syzkaller reported the following issue:
=======================================
Too BIG xdp->frame_sz = 131072
WARNING: CPU: 0 PID: 5020 at net/core/filter.c:4121
____bpf_xdp_adjust_tail net/core/filter.c:4121 [inline]
WARNING: CPU: 0 PID: 5020 at net/core/filter.c:4121
bpf_xdp_adjust_tail+0x466/0xa10 net/core/filter.c:4103
...
Call Trace:
<TASK>
bpf_prog_4add87e5301a4105+0x1a/0x1c
__bpf_prog_run include/linux/filter.h:600 [inline]
bpf_prog_run_xdp include/linux/filter.h:775 [inline]
bpf_prog_run_generic_xdp+0x57e/0x11e0 net/core/dev.c:4721
netif_receive_generic_xdp net/core/dev.c:4807 [inline]
do_xdp_generic+0x35c/0x770 net/core/dev.c:4866
tun_get_user+0x2340/0x3ca0 drivers/net/tun.c:1919
tun_chr_write_iter+0xe8/0x210 drivers/net/tun.c:2043
call_write_iter include/linux/fs.h:1871 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x650/0xe40 fs/read_write.c:584
ksys_write+0x12f/0x250 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
xdp->frame_sz > PAGE_SIZE check was introduced in commit c8741e2bfe87
("xdp: Allow bpf_xdp_adjust_tail() to grow packet size"). But Jesper
Dangaard Brouer <jbrouer@redhat.com> noted that after introducing the
xdp_init_buff() which all XDP driver use - it's safe to remove this
check. The original intend was to catch cases where XDP drivers have
not been updated to use xdp.frame_sz, but that is not longer a concern
(since xdp_init_buff).
Running the initial syzkaller repro it was discovered that the
contiguous physical memory allocation is used for both xdp paths in
tun_get_user(), e.g. tun_build_skb() and tun_alloc_skb(). It was also
stated by Jesper Dangaard Brouer <jbrouer@redhat.com> that XDP can
work on higher order pages, as long as this is contiguous physical
memory (e.g. a page).
Reported-and-tested-by: syzbot+f817490f5bd20541b90a@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000774b9205f1d8a80d@google.com/T/
Link: https://syzkaller.appspot.com/bug?extid=f817490f5bd20541b90a
Link: https://lore.kernel.org/all/20230725155403.796-1-andrew.kanner@gmail.com/T/
Fixes: 43b5169d8355 ("net, xdp: Introduce xdp_init_buff utility routine")
Signed-off-by: Andrew Kanner <andrew.kanner@gmail.com>
---
net/core/filter.c | 6 ------
1 file changed, 6 deletions(-)
diff --git a/net/core/filter.c b/net/core/filter.c
index 06ba0e56e369..28a59596987a 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4116,12 +4116,6 @@ BPF_CALL_2(bpf_xdp_adjust_tail, struct xdp_buff *, xdp, int, offset)
if (unlikely(data_end > data_hard_end))
return -EINVAL;
- /* ALL drivers MUST init xdp->frame_sz, chicken check below */
- if (unlikely(xdp->frame_sz > PAGE_SIZE)) {
- WARN_ONCE(1, "Too BIG xdp->frame_sz = %d\n", xdp->frame_sz);
- return -EINVAL;
- }
-
if (unlikely(data_end < xdp->data + ETH_HLEN))
return -EINVAL;
--
2.39.3
^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit
2023-08-01 22:07 [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit Andrew Kanner
2023-08-01 22:07 ` [PATCH v4 2/2] net: core: remove unnecessary frame_sz check in bpf_xdp_adjust_tail() Andrew Kanner
@ 2023-08-02 1:07 ` David Ahern
2023-08-02 12:16 ` Andrew Kanner
2023-08-02 14:13 ` Jesper Dangaard Brouer
2 siblings, 1 reply; 11+ messages in thread
From: David Ahern @ 2023-08-02 1:07 UTC (permalink / raw)
To: Andrew Kanner, davem, edumazet, kuba, pabeni, jasowang, netdev,
brouer, jbrouer, john.fastabend, linux-kernel
Cc: linux-kernel-mentees, syzbot+f817490f5bd20541b90a
On 8/1/23 4:07 PM, Andrew Kanner wrote:
> @@ -1594,7 +1597,13 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
> if (zerocopy)
> return false;
>
> - if (SKB_DATA_ALIGN(len + TUN_RX_PAD) +
> + rcu_read_lock();
> + xdp_prog = rcu_dereference(tun->xdp_prog);
> + if (xdp_prog)
> + pad += XDP_PACKET_HEADROOM;
> + rcu_read_unlock();
since you do not care about the actual xdp_prog (only that one is set) I
believe you can use rcu_access_pointer here.
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit
2023-08-02 1:07 ` [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit David Ahern
@ 2023-08-02 12:16 ` Andrew Kanner
0 siblings, 0 replies; 11+ messages in thread
From: Andrew Kanner @ 2023-08-02 12:16 UTC (permalink / raw)
To: David Ahern
Cc: davem, edumazet, kuba, pabeni, jasowang, netdev, brouer, jbrouer,
john.fastabend, linux-kernel, linux-kernel-mentees,
syzbot+f817490f5bd20541b90a
On Tue, Aug 01, 2023 at 07:07:39PM -0600, David Ahern wrote:
> On 8/1/23 4:07 PM, Andrew Kanner wrote:
> > @@ -1594,7 +1597,13 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
> > if (zerocopy)
> > return false;
> >
> > - if (SKB_DATA_ALIGN(len + TUN_RX_PAD) +
> > + rcu_read_lock();
> > + xdp_prog = rcu_dereference(tun->xdp_prog);
> > + if (xdp_prog)
> > + pad += XDP_PACKET_HEADROOM;
> > + rcu_read_unlock();
>
>
> since you do not care about the actual xdp_prog (only that one is set) I
> believe you can use rcu_access_pointer here.
Good point. Thanks, David.
I'll resend both as v5.
The correct cc-list for PATCH 2/2 is also needed. It fixes
net/core/filter.c instead of drivers/net/tun.c now.
pw-bot: changes-requested
--
Andrew Kanner
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v4 2/2] net: core: remove unnecessary frame_sz check in bpf_xdp_adjust_tail()
2023-08-01 22:07 ` [PATCH v4 2/2] net: core: remove unnecessary frame_sz check in bpf_xdp_adjust_tail() Andrew Kanner
@ 2023-08-02 13:56 ` Jesper Dangaard Brouer
2023-08-03 3:20 ` Jason Wang
1 sibling, 0 replies; 11+ messages in thread
From: Jesper Dangaard Brouer @ 2023-08-02 13:56 UTC (permalink / raw)
To: Andrew Kanner, davem, edumazet, kuba, pabeni, jasowang, netdev,
dsahern, jbrouer, john.fastabend, linux-kernel
Cc: linux-kernel-mentees, syzbot+f817490f5bd20541b90a
On 02/08/2023 00.07, Andrew Kanner wrote:
> Syzkaller reported the following issue:
> =======================================
> Too BIG xdp->frame_sz = 131072
> WARNING: CPU: 0 PID: 5020 at net/core/filter.c:4121
> ____bpf_xdp_adjust_tail net/core/filter.c:4121 [inline]
> WARNING: CPU: 0 PID: 5020 at net/core/filter.c:4121
> bpf_xdp_adjust_tail+0x466/0xa10 net/core/filter.c:4103
> ...
> Call Trace:
> <TASK>
> bpf_prog_4add87e5301a4105+0x1a/0x1c
> __bpf_prog_run include/linux/filter.h:600 [inline]
> bpf_prog_run_xdp include/linux/filter.h:775 [inline]
> bpf_prog_run_generic_xdp+0x57e/0x11e0 net/core/dev.c:4721
> netif_receive_generic_xdp net/core/dev.c:4807 [inline]
> do_xdp_generic+0x35c/0x770 net/core/dev.c:4866
> tun_get_user+0x2340/0x3ca0 drivers/net/tun.c:1919
> tun_chr_write_iter+0xe8/0x210 drivers/net/tun.c:2043
> call_write_iter include/linux/fs.h:1871 [inline]
> new_sync_write fs/read_write.c:491 [inline]
> vfs_write+0x650/0xe40 fs/read_write.c:584
> ksys_write+0x12f/0x250 fs/read_write.c:637
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> xdp->frame_sz > PAGE_SIZE check was introduced in commit c8741e2bfe87
> ("xdp: Allow bpf_xdp_adjust_tail() to grow packet size"). But Jesper
> Dangaard Brouer <jbrouer@redhat.com> noted that after introducing the
> xdp_init_buff() which all XDP driver use - it's safe to remove this
> check. The original intend was to catch cases where XDP drivers have
> not been updated to use xdp.frame_sz, but that is not longer a concern
> (since xdp_init_buff).
>
> Running the initial syzkaller repro it was discovered that the
> contiguous physical memory allocation is used for both xdp paths in
> tun_get_user(), e.g. tun_build_skb() and tun_alloc_skb(). It was also
> stated by Jesper Dangaard Brouer <jbrouer@redhat.com> that XDP can
> work on higher order pages, as long as this is contiguous physical
> memory (e.g. a page).
>
> Reported-and-tested-by: syzbot+f817490f5bd20541b90a@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/000000000000774b9205f1d8a80d@google.com/T/
> Link: https://syzkaller.appspot.com/bug?extid=f817490f5bd20541b90a
> Link: https://lore.kernel.org/all/20230725155403.796-1-andrew.kanner@gmail.com/T/
> Fixes: 43b5169d8355 ("net, xdp: Introduce xdp_init_buff utility routine")
> Signed-off-by: Andrew Kanner <andrew.kanner@gmail.com>
> ---
Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>
You can include that ACK in V5.
> net/core/filter.c | 6 ------
> 1 file changed, 6 deletions(-)
>
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 06ba0e56e369..28a59596987a 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4116,12 +4116,6 @@ BPF_CALL_2(bpf_xdp_adjust_tail, struct xdp_buff *, xdp, int, offset)
> if (unlikely(data_end > data_hard_end))
> return -EINVAL;
>
> - /* ALL drivers MUST init xdp->frame_sz, chicken check below */
> - if (unlikely(xdp->frame_sz > PAGE_SIZE)) {
> - WARN_ONCE(1, "Too BIG xdp->frame_sz = %d\n", xdp->frame_sz);
> - return -EINVAL;
> - }
> -
> if (unlikely(data_end < xdp->data + ETH_HLEN))
> return -EINVAL;
>
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit
2023-08-01 22:07 [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit Andrew Kanner
2023-08-01 22:07 ` [PATCH v4 2/2] net: core: remove unnecessary frame_sz check in bpf_xdp_adjust_tail() Andrew Kanner
2023-08-02 1:07 ` [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit David Ahern
@ 2023-08-02 14:13 ` Jesper Dangaard Brouer
2023-08-03 3:19 ` Jason Wang
2 siblings, 1 reply; 11+ messages in thread
From: Jesper Dangaard Brouer @ 2023-08-02 14:13 UTC (permalink / raw)
To: Andrew Kanner, davem, edumazet, kuba, pabeni, jasowang, netdev,
dsahern, jbrouer, john.fastabend, linux-kernel
Cc: linux-kernel-mentees, syzbot+f817490f5bd20541b90a
On 02/08/2023 00.07, Andrew Kanner wrote:
> Using the syzkaller repro with reduced packet size it was discovered
> that XDP_PACKET_HEADROOM is not checked in tun_can_build_skb(),
> although pad may be incremented in tun_build_skb(). This may end up
> with exceeding the PAGE_SIZE limit in tun_build_skb().
>
> Fixes: 7df13219d757 ("tun: reserve extra headroom only when XDP is set")
> Link: https://syzkaller.appspot.com/bug?extid=f817490f5bd20541b90a
> Signed-off-by: Andrew Kanner <andrew.kanner@gmail.com>
> ---
>
> Notes:
> v3 -> v4:
> * fall back to v1, fixing only missing XDP_PACKET_HEADROOM in pad and
> removing bpf_xdp_adjust_tail() check for frame_sz.
> * added rcu read lock, noted by Jason Wang <jasowang@redhat.com> in v1
> * I decided to leave the packet length check in tun_can_build_skb()
> instead of moving to tun_build_skb() suggested by Jason Wang
> <jasowang@redhat.com>. Otherwise extra packets will be dropped
> without falling back to tun_alloc_skb(). And in the discussion of v3
> Jesper Dangaard Brouer <jbrouer@redhat.com> noticed that XDP is ok
> with a higher order pages if it's a contiguous physical memory
> allocation, so falling to tun_alloc_skb() -> do_xdp_generic() should
> be ok.
>
> v2 -> v3:
> * attach the forgotten changelog
>
> v1 -> v2:
> * merged 2 patches in 1, fixing both issues: WARN_ON_ONCE with
> syzkaller repro and missing XDP_PACKET_HEADROOM in pad
> * changed the title and description of the execution path, suggested
> by Jason Wang <jasowang@redhat.com>
> * move the limit check from tun_can_build_skb() to tun_build_skb() to
> remove duplication and locking issue, and also drop the packet in
> case of a failed check - noted by Jason Wang <jasowang@redhat.com>
>
> drivers/net/tun.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index d75456adc62a..a1d04bc9485f 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1582,6 +1582,9 @@ static void tun_rx_batched(struct tun_struct *tun, struct tun_file *tfile,
> static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
> int len, int noblock, bool zerocopy)
> {
> + struct bpf_prog *xdp_prog;
> + int pad = TUN_RX_PAD;
> +
> if ((tun->flags & TUN_TYPE_MASK) != IFF_TAP)
> return false;
>
> @@ -1594,7 +1597,13 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
> if (zerocopy)
> return false;
>
> - if (SKB_DATA_ALIGN(len + TUN_RX_PAD) +
> + rcu_read_lock();
> + xdp_prog = rcu_dereference(tun->xdp_prog);
> + if (xdp_prog)
> + pad += XDP_PACKET_HEADROOM;
> + rcu_read_unlock();
> +
Isolated seen, I guess, this is a correct fix to 7df13219d757.
> + if (SKB_DATA_ALIGN(len + pad) +
> SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) > PAGE_SIZE)
> return false;
>
Question to Jason Wang:
Why fall back (to e.g. tun_alloc_skb()) when size is above PAGE_SIZE?
AFAIK tun_build_skb() *can* create get larger packets than PAGE_SIZE
from it's page_frag. Is there a reason for this limitation?
(To Andrew, I assume a change in this area is another patch).
--Jesper
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit
2023-08-02 14:13 ` Jesper Dangaard Brouer
@ 2023-08-03 3:19 ` Jason Wang
2023-08-03 17:53 ` Andrew Kanner
0 siblings, 1 reply; 11+ messages in thread
From: Jason Wang @ 2023-08-03 3:19 UTC (permalink / raw)
To: Jesper Dangaard Brouer
Cc: Andrew Kanner, davem, edumazet, kuba, pabeni, netdev, dsahern,
jbrouer, john.fastabend, linux-kernel, linux-kernel-mentees,
syzbot+f817490f5bd20541b90a
On Wed, Aug 2, 2023 at 10:14 PM Jesper Dangaard Brouer <hawk@kernel.org> wrote:
>
>
>
> On 02/08/2023 00.07, Andrew Kanner wrote:
> > Using the syzkaller repro with reduced packet size it was discovered
> > that XDP_PACKET_HEADROOM is not checked in tun_can_build_skb(),
> > although pad may be incremented in tun_build_skb(). This may end up
> > with exceeding the PAGE_SIZE limit in tun_build_skb().
> >
> > Fixes: 7df13219d757 ("tun: reserve extra headroom only when XDP is set")
> > Link: https://syzkaller.appspot.com/bug?extid=f817490f5bd20541b90a
> > Signed-off-by: Andrew Kanner <andrew.kanner@gmail.com>
> > ---
> >
> > Notes:
> > v3 -> v4:
> > * fall back to v1, fixing only missing XDP_PACKET_HEADROOM in pad and
> > removing bpf_xdp_adjust_tail() check for frame_sz.
> > * added rcu read lock, noted by Jason Wang <jasowang@redhat.com> in v1
> > * I decided to leave the packet length check in tun_can_build_skb()
> > instead of moving to tun_build_skb() suggested by Jason Wang
> > <jasowang@redhat.com>. Otherwise extra packets will be dropped
> > without falling back to tun_alloc_skb(). And in the discussion of v3
> > Jesper Dangaard Brouer <jbrouer@redhat.com> noticed that XDP is ok
> > with a higher order pages if it's a contiguous physical memory
> > allocation, so falling to tun_alloc_skb() -> do_xdp_generic() should
> > be ok.
> >
> > v2 -> v3:
> > * attach the forgotten changelog
> >
> > v1 -> v2:
> > * merged 2 patches in 1, fixing both issues: WARN_ON_ONCE with
> > syzkaller repro and missing XDP_PACKET_HEADROOM in pad
> > * changed the title and description of the execution path, suggested
> > by Jason Wang <jasowang@redhat.com>
> > * move the limit check from tun_can_build_skb() to tun_build_skb() to
> > remove duplication and locking issue, and also drop the packet in
> > case of a failed check - noted by Jason Wang <jasowang@redhat.com>
> >
> > drivers/net/tun.c | 11 ++++++++++-
> > 1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> > index d75456adc62a..a1d04bc9485f 100644
> > --- a/drivers/net/tun.c
> > +++ b/drivers/net/tun.c
> > @@ -1582,6 +1582,9 @@ static void tun_rx_batched(struct tun_struct *tun, struct tun_file *tfile,
> > static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
> > int len, int noblock, bool zerocopy)
> > {
> > + struct bpf_prog *xdp_prog;
> > + int pad = TUN_RX_PAD;
> > +
> > if ((tun->flags & TUN_TYPE_MASK) != IFF_TAP)
> > return false;
> >
> > @@ -1594,7 +1597,13 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
> > if (zerocopy)
> > return false;
> >
> > - if (SKB_DATA_ALIGN(len + TUN_RX_PAD) +
> > + rcu_read_lock();
> > + xdp_prog = rcu_dereference(tun->xdp_prog);
> > + if (xdp_prog)
> > + pad += XDP_PACKET_HEADROOM;
> > + rcu_read_unlock();
> > +
>
> Isolated seen, I guess, this is a correct fix to 7df13219d757.
I think so.
Actually, I think we can probably always count XDP_PACKET_HEADROOM
here. Since there's a window that XDP program might be attached in the
middle of tun_can_build_skb() and tun_build_skb().
>
> > + if (SKB_DATA_ALIGN(len + pad) +
> > SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) > PAGE_SIZE)
> > return false;
> >
>
> Question to Jason Wang:
> Why fall back (to e.g. tun_alloc_skb()) when size is above PAGE_SIZE?
>
> AFAIK tun_build_skb() *can* create get larger packets than PAGE_SIZE
> from it's page_frag. Is there a reason for this limitation?
I couldn't recall but I think we can relax.
Thanks
>
> (To Andrew, I assume a change in this area is another patch).
>
> --Jesper
>
>
>
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v4 2/2] net: core: remove unnecessary frame_sz check in bpf_xdp_adjust_tail()
2023-08-01 22:07 ` [PATCH v4 2/2] net: core: remove unnecessary frame_sz check in bpf_xdp_adjust_tail() Andrew Kanner
2023-08-02 13:56 ` Jesper Dangaard Brouer
@ 2023-08-03 3:20 ` Jason Wang
2023-08-03 18:06 ` Andrew Kanner
1 sibling, 1 reply; 11+ messages in thread
From: Jason Wang @ 2023-08-03 3:20 UTC (permalink / raw)
To: Andrew Kanner
Cc: davem, edumazet, kuba, pabeni, netdev, brouer, dsahern, jbrouer,
john.fastabend, linux-kernel, linux-kernel-mentees,
syzbot+f817490f5bd20541b90a
On Wed, Aug 2, 2023 at 6:09 AM Andrew Kanner <andrew.kanner@gmail.com> wrote:
>
> Syzkaller reported the following issue:
> =======================================
> Too BIG xdp->frame_sz = 131072
> WARNING: CPU: 0 PID: 5020 at net/core/filter.c:4121
> ____bpf_xdp_adjust_tail net/core/filter.c:4121 [inline]
> WARNING: CPU: 0 PID: 5020 at net/core/filter.c:4121
> bpf_xdp_adjust_tail+0x466/0xa10 net/core/filter.c:4103
> ...
> Call Trace:
> <TASK>
> bpf_prog_4add87e5301a4105+0x1a/0x1c
> __bpf_prog_run include/linux/filter.h:600 [inline]
> bpf_prog_run_xdp include/linux/filter.h:775 [inline]
> bpf_prog_run_generic_xdp+0x57e/0x11e0 net/core/dev.c:4721
> netif_receive_generic_xdp net/core/dev.c:4807 [inline]
> do_xdp_generic+0x35c/0x770 net/core/dev.c:4866
> tun_get_user+0x2340/0x3ca0 drivers/net/tun.c:1919
> tun_chr_write_iter+0xe8/0x210 drivers/net/tun.c:2043
> call_write_iter include/linux/fs.h:1871 [inline]
> new_sync_write fs/read_write.c:491 [inline]
> vfs_write+0x650/0xe40 fs/read_write.c:584
> ksys_write+0x12f/0x250 fs/read_write.c:637
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> xdp->frame_sz > PAGE_SIZE check was introduced in commit c8741e2bfe87
> ("xdp: Allow bpf_xdp_adjust_tail() to grow packet size"). But Jesper
> Dangaard Brouer <jbrouer@redhat.com> noted that after introducing the
> xdp_init_buff() which all XDP driver use - it's safe to remove this
> check. The original intend was to catch cases where XDP drivers have
> not been updated to use xdp.frame_sz, but that is not longer a concern
> (since xdp_init_buff).
>
> Running the initial syzkaller repro it was discovered that the
> contiguous physical memory allocation is used for both xdp paths in
> tun_get_user(), e.g. tun_build_skb() and tun_alloc_skb(). It was also
> stated by Jesper Dangaard Brouer <jbrouer@redhat.com> that XDP can
> work on higher order pages, as long as this is contiguous physical
> memory (e.g. a page).
>
> Reported-and-tested-by: syzbot+f817490f5bd20541b90a@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/000000000000774b9205f1d8a80d@google.com/T/
> Link: https://syzkaller.appspot.com/bug?extid=f817490f5bd20541b90a
> Link: https://lore.kernel.org/all/20230725155403.796-1-andrew.kanner@gmail.com/T/
> Fixes: 43b5169d8355 ("net, xdp: Introduce xdp_init_buff utility routine")
> Signed-off-by: Andrew Kanner <andrew.kanner@gmail.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Thanks
> ---
> net/core/filter.c | 6 ------
> 1 file changed, 6 deletions(-)
>
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 06ba0e56e369..28a59596987a 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4116,12 +4116,6 @@ BPF_CALL_2(bpf_xdp_adjust_tail, struct xdp_buff *, xdp, int, offset)
> if (unlikely(data_end > data_hard_end))
> return -EINVAL;
>
> - /* ALL drivers MUST init xdp->frame_sz, chicken check below */
> - if (unlikely(xdp->frame_sz > PAGE_SIZE)) {
> - WARN_ONCE(1, "Too BIG xdp->frame_sz = %d\n", xdp->frame_sz);
> - return -EINVAL;
> - }
> -
> if (unlikely(data_end < xdp->data + ETH_HLEN))
> return -EINVAL;
>
> --
> 2.39.3
>
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit
2023-08-03 3:19 ` Jason Wang
@ 2023-08-03 17:53 ` Andrew Kanner
2023-08-04 9:30 ` Jesper Dangaard Brouer
0 siblings, 1 reply; 11+ messages in thread
From: Andrew Kanner @ 2023-08-03 17:53 UTC (permalink / raw)
To: Jason Wang, Jesper Dangaard Brouer
Cc: davem, edumazet, kuba, pabeni, netdev, dsahern, jbrouer,
john.fastabend, linux-kernel, linux-kernel-mentees,
syzbot+f817490f5bd20541b90a
On Thu, Aug 03, 2023 at 11:19:47AM +0800, Jason Wang wrote:
> > > @@ -1594,7 +1597,13 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
> > > if (zerocopy)
> > > return false;
> > >
> > > - if (SKB_DATA_ALIGN(len + TUN_RX_PAD) +
> > > + rcu_read_lock();
> > > + xdp_prog = rcu_dereference(tun->xdp_prog);
> > > + if (xdp_prog)
> > > + pad += XDP_PACKET_HEADROOM;
> > > + rcu_read_unlock();
> > > +
> >
> > Isolated seen, I guess, this is a correct fix to 7df13219d757.
>
> I think so.
>
> Actually, I think we can probably always count XDP_PACKET_HEADROOM
> here. Since there's a window that XDP program might be attached in the
> middle of tun_can_build_skb() and tun_build_skb().
Thanks, that makes sense.
I will do it in v5.
> > Question to Jason Wang:
> > Why fall back (to e.g. tun_alloc_skb()) when size is above PAGE_SIZE?
> >
> > AFAIK tun_build_skb() *can* create get larger packets than PAGE_SIZE
> > from it's page_frag. Is there a reason for this limitation?
>
> I couldn't recall but I think we can relax.
Jesper already sent enough info for this idea in v2, I will use it for
the next patch/series.
Jesper, I will add this tag for this next patch/series if you don't
mind:
Suggested-by: Jesper Dangaard Brouer <hawk@kernel.org>
--
Andrew Kanner
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v4 2/2] net: core: remove unnecessary frame_sz check in bpf_xdp_adjust_tail()
2023-08-03 3:20 ` Jason Wang
@ 2023-08-03 18:06 ` Andrew Kanner
0 siblings, 0 replies; 11+ messages in thread
From: Andrew Kanner @ 2023-08-03 18:06 UTC (permalink / raw)
To: Jason Wang
Cc: davem, edumazet, kuba, pabeni, netdev, brouer, dsahern, jbrouer,
john.fastabend, linux-kernel, linux-kernel-mentees,
syzbot+f817490f5bd20541b90a
On Thu, Aug 03, 2023 at 11:20:20AM +0800, Jason Wang wrote:
>
> Acked-by: Jason Wang <jasowang@redhat.com>
>
> Thanks
>
Thanks, Jason.
I will use this tag in v5, if you don't mind.
PATCH 2/2 will be the same but with more recipients.
--
Andrew Kanner
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit
2023-08-03 17:53 ` Andrew Kanner
@ 2023-08-04 9:30 ` Jesper Dangaard Brouer
0 siblings, 0 replies; 11+ messages in thread
From: Jesper Dangaard Brouer @ 2023-08-04 9:30 UTC (permalink / raw)
To: Andrew Kanner, Jason Wang
Cc: davem, edumazet, kuba, pabeni, netdev, dsahern, jbrouer,
john.fastabend, linux-kernel, linux-kernel-mentees,
syzbot+f817490f5bd20541b90a, Alexander Duyck
On 03/08/2023 19.53, Andrew Kanner wrote:
>>> Question to Jason Wang:
>>> Why fall back (to e.g. tun_alloc_skb()) when size is above PAGE_SIZE?
>>>
>>> AFAIK tun_build_skb()*can* create get larger packets than PAGE_SIZE
>>> from it's page_frag. Is there a reason for this limitation?
>> >> I couldn't recall but I think we can relax.
> > Jesper already sent enough info for this idea in v2, I will use it for
> the next patch/series.
>
I have some more input and considerations when selecting the new
constant that replace PAGE_SIZE.
Lets see if Eric Dumazet or Alex Duyck disagree?
("inventors" of page_frag scheme)
The function tun_alloc_skb() uses a page_frag scheme for allocation.
The maximim size is 32768 bytes (Order-3), but using something that is
close to this max alloc size can cause memory waste and fragmentation.
My suggestion would be to use the constant SKB_MAX_ALLOC (16KiB).
Maybe Eric or Alex would recommend using something smaller? (e.g. 8192)
page_frag limit comes from:
#define SKB_FRAG_PAGE_ORDER get_order(32768)
> Jesper, I will add this tag for this next patch/series if you don't
> mind:
> Suggested-by: Jesper Dangaard Brouer <hawk@kernel.org>
ACK
^ permalink raw reply [flat|nested] 11+ messages in thread
end of thread, other threads:[~2023-08-04 9:30 UTC | newest]
Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-08-01 22:07 [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit Andrew Kanner
2023-08-01 22:07 ` [PATCH v4 2/2] net: core: remove unnecessary frame_sz check in bpf_xdp_adjust_tail() Andrew Kanner
2023-08-02 13:56 ` Jesper Dangaard Brouer
2023-08-03 3:20 ` Jason Wang
2023-08-03 18:06 ` Andrew Kanner
2023-08-02 1:07 ` [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit David Ahern
2023-08-02 12:16 ` Andrew Kanner
2023-08-02 14:13 ` Jesper Dangaard Brouer
2023-08-03 3:19 ` Jason Wang
2023-08-03 17:53 ` Andrew Kanner
2023-08-04 9:30 ` Jesper Dangaard Brouer
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).