From: Arjun Roy <hidden> Date: 2021-11-11 23:52:22
From: Arjun Roy <redacted>
TCP Receive zerocopy iterates through the SKB queue via
tcp_recv_skb(), acquiring a pointer to an SKB and an offset within
that SKB to read from. From there, it iterates the SKB frags array to
determine which offset to start remapping pages from.
However, this is built on the assumption that the offset read so far
within the SKB is smaller than the SKB length. If this assumption is
violated, we can attempt to read an invalid frags array element, which
would cause a fault.
tcp_recv_skb() can cause such an SKB to be returned when the TCP FIN
flag is set. Therefore, we must guard against this occurrence inside
skb_advance_frag().
One way that we can reproduce this error follows:
1) In a receiver program, call getsockopt(TCP_ZEROCOPY_RECEIVE) with:
char some_array[32 * 1024];
struct tcp_zerocopy_receive zc = {
.copybuf_address = (__u64) &some_array[0],
.copybuf_len = 32 * 1024,
};
2) In a sender program, after a TCP handshake, send the following
sequence of packets:
i) Seq = [X, X+4000]
ii) Seq = [X+4000, X+5000]
iii) Seq = [X+4000, X+5000], Flags = FIN | URG, urgptr=1000
(This can happen without URG, if we have a signal pending, but URG is
a convenient way to reproduce the behaviour).
In this case, the following event sequence will occur on the receiver:
tcp_zerocopy_receive():
-> receive_fallback_to_copy() // copybuf_len >= inq
-> tcp_recvmsg_locked() // reads 5000 bytes, then breaks due to URG
-> tcp_recv_skb() // yields skb with skb->len == offset
-> tcp_zerocopy_set_hint_for_skb()
-> skb_advance_to_frag() // will returns a frags ptr. >= nr_frags
-> find_next_mappable_frag() // will dereference this bad frags ptr.
With this patch, skb_advance_to_frag() will no longer return an
invalid frags pointer, and will return NULL instead, fixing the issue.
Signed-off-by: Arjun Roy <redacted>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Fixes: 05255b823a61 ("tcp: add TCP_ZEROCOPY_RECEIVE support for zerocopy receive")
---
net/ipv4/tcp.c | 3 +++
1 file changed, 3 insertions(+)
From: Arjun Roy <hidden> Date: 2021-11-12 02:32:37
On Thu, Nov 11, 2021 at 3:52 PM Arjun Roy [off-list ref] wrote:
quoted hunk
From: Arjun Roy <redacted>
TCP Receive zerocopy iterates through the SKB queue via
tcp_recv_skb(), acquiring a pointer to an SKB and an offset within
that SKB to read from. From there, it iterates the SKB frags array to
determine which offset to start remapping pages from.
However, this is built on the assumption that the offset read so far
within the SKB is smaller than the SKB length. If this assumption is
violated, we can attempt to read an invalid frags array element, which
would cause a fault.
tcp_recv_skb() can cause such an SKB to be returned when the TCP FIN
flag is set. Therefore, we must guard against this occurrence inside
skb_advance_frag().
One way that we can reproduce this error follows:
1) In a receiver program, call getsockopt(TCP_ZEROCOPY_RECEIVE) with:
char some_array[32 * 1024];
struct tcp_zerocopy_receive zc = {
.copybuf_address = (__u64) &some_array[0],
.copybuf_len = 32 * 1024,
};
2) In a sender program, after a TCP handshake, send the following
sequence of packets:
i) Seq = [X, X+4000]
ii) Seq = [X+4000, X+5000]
iii) Seq = [X+4000, X+5000], Flags = FIN | URG, urgptr=1000
(This can happen without URG, if we have a signal pending, but URG is
a convenient way to reproduce the behaviour).
In this case, the following event sequence will occur on the receiver:
tcp_zerocopy_receive():
-> receive_fallback_to_copy() // copybuf_len >= inq
-> tcp_recvmsg_locked() // reads 5000 bytes, then breaks due to URG
-> tcp_recv_skb() // yields skb with skb->len == offset
-> tcp_zerocopy_set_hint_for_skb()
-> skb_advance_to_frag() // will returns a frags ptr. >= nr_frags
-> find_next_mappable_frag() // will dereference this bad frags ptr.
With this patch, skb_advance_to_frag() will no longer return an
invalid frags pointer, and will return NULL instead, fixing the issue.
Signed-off-by: Arjun Roy <redacted>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Fixes: 05255b823a61 ("tcp: add TCP_ZEROCOPY_RECEIVE support for zerocopy receive")
---
net/ipv4/tcp.c | 3 +++
1 file changed, 3 insertions(+)
From: Jakub Kicinski <kuba@kernel.org> Date: 2021-11-13 03:43:13
On Thu, 11 Nov 2021 18:32:23 -0800 Arjun Roy wrote:
On Thu, Nov 11, 2021 at 3:52 PM Arjun Roy [off-list ref] wrote:
quoted
From: Arjun Roy <redacted>
TCP Receive zerocopy iterates through the SKB queue via
tcp_recv_skb(), acquiring a pointer to an SKB and an offset within
that SKB to read from. From there, it iterates the SKB frags array to
determine which offset to start remapping pages from.
However, this is built on the assumption that the offset read so far
within the SKB is smaller than the SKB length. If this assumption is
violated, we can attempt to read an invalid frags array element, which
would cause a fault.
tcp_recv_skb() can cause such an SKB to be returned when the TCP FIN
flag is set. Therefore, we must guard against this occurrence inside
skb_advance_frag().
One way that we can reproduce this error follows:
1) In a receiver program, call getsockopt(TCP_ZEROCOPY_RECEIVE) with:
char some_array[32 * 1024];
struct tcp_zerocopy_receive zc = {
.copybuf_address = (__u64) &some_array[0],
.copybuf_len = 32 * 1024,
};
2) In a sender program, after a TCP handshake, send the following
sequence of packets:
i) Seq = [X, X+4000]
ii) Seq = [X+4000, X+5000]
iii) Seq = [X+4000, X+5000], Flags = FIN | URG, urgptr=1000
(This can happen without URG, if we have a signal pending, but URG is
a convenient way to reproduce the behaviour).
In this case, the following event sequence will occur on the receiver:
tcp_zerocopy_receive():
-> receive_fallback_to_copy() // copybuf_len >= inq
-> tcp_recvmsg_locked() // reads 5000 bytes, then breaks due to URG
-> tcp_recv_skb() // yields skb with skb->len == offset
-> tcp_zerocopy_set_hint_for_skb()
-> skb_advance_to_frag() // will returns a frags ptr. >= nr_frags
-> find_next_mappable_frag() // will dereference this bad frags ptr.
With this patch, skb_advance_to_frag() will no longer return an
invalid frags pointer, and will return NULL instead, fixing the issue.
Signed-off-by: Arjun Roy <redacted>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Fixes: 05255b823a61 ("tcp: add TCP_ZEROCOPY_RECEIVE support for zerocopy receive")
---
net/ipv4/tcp.c | 3 +++
1 file changed, 3 insertions(+)
Hello:
This patch was applied to netdev/net.git (master)
by Jakub Kicinski [off-list ref]:
On Thu, 11 Nov 2021 15:52:15 -0800 you wrote:
From: Arjun Roy <redacted>
TCP Receive zerocopy iterates through the SKB queue via
tcp_recv_skb(), acquiring a pointer to an SKB and an offset within
that SKB to read from. From there, it iterates the SKB frags array to
determine which offset to start remapping pages from.
[...]