[PATCH 5.12 040/178] skbuff: fix incorrect msg_zerocopy copy notifications

Greg Kroah-Hartman
2021-06-21T16:39:20Z

From: Willem de Bruijn <willemb@google.com>

[ Upstream commit 3bdd5ee0ec8c14131d560da492e6df452c6fdd75 ]

msg_zerocopy signals if a send operation required copying with a flag
in serr->ee.ee_code.

This field can be incorrect as of the below commit, as a result of
both structs uarg and serr pointing into the same skb->cb[].

uarg->zerocopy must be read before skb->cb[] is reinitialized to hold
serr. Similar to other fields len, hi and lo, use a local variable to
temporarily hold the value.

This was not a problem before, when the value was passed as a function
argument.

Fixes: 75518851a2a0 ("skbuff: Push status and refcounts into sock_zerocopy_callback")
Reported-by: Talal Ahmad <talalahmad@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/core/skbuff.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index c421c8f80925..7997d99afbd8 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1252,6 +1252,7 @@ static void __msg_zerocopy_callback(struct ubuf_info *uarg)
struct sock *sk = skb->sk;
struct sk_buff_head *q;
unsigned long flags;
+ bool is_zerocopy;
u32 lo, hi;
u16 len;

@@ -1266,6 +1267,7 @@ static void __msg_zerocopy_callback(struct ubuf_info *uarg)
len = uarg->len;
lo = uarg->id;
hi = uarg->id + len - 1;
+ is_zerocopy = uarg->zerocopy;

serr = SKB_EXT_ERR(skb);
memset(serr, 0, sizeof(*serr));
@@ -1273,7 +1275,7 @@ static void __msg_zerocopy_callback(struct ubuf_info *uarg)
serr->ee.ee_origin = SO_EE_ORIGIN_ZEROCOPY;
serr->ee.ee_data = hi;
serr->ee.ee_info = lo;
- if (!uarg->zerocopy)
+ if (!is_zerocopy)
serr->ee.ee_code |= SO_EE_CODE_ZEROCOPY_COPIED;

q = &sk->sk_error_queue;
--
2.30.2