6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Stanislav Fomichev <sdf@xxxxxxxxxxx>
[ Upstream commit 18912c520674ec4d920fe3826e7e4fefeecdf5ae ]
Currently, we report -ETOOSMALL (err) only on the first iteration
(!sent). When we get put_cmsg error after a bunch of successful
put_cmsg calls, we don't signal the error at all. This might be
confusing on the userspace side which will see truncated CMSGs
but no MSG_CTRUNC signal.
Consider the following case:
- sizeof(struct cmsghdr) = 16
- sizeof(struct dmabuf_cmsg) = 24
- total cmsg size (CMSG_LEN) = 40 (16+24)
When calling recvmsg with msg_controllen=60, the userspace
will receive two(!) dmabuf_cmsg(s), the first one will
be a valid one and the second one will be silently truncated. There is no
easy way to discover the truncation besides doing something like
"cm->cmsg_len != CMSG_LEN(sizeof(dmabuf_cmsg))".
Introduce new put_devmem_cmsg wrapper that reports an error instead
of doing the truncation. Mina suggests that it's the intended way
this API should work.
Note that we might now report MSG_CTRUNC when the users (incorrectly)
call us with msg_control == NULL.
Fixes: 8f0b3cc9a4c1 ("tcp: RX path for devmem TCP")
Reviewed-by: Mina Almasry <almasrymina@xxxxxxxxxx>
Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Link: https://patch.msgid.link/20250224174401.3582695-1-sdf@xxxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
include/linux/socket.h | 2 ++
net/core/scm.c | 10 ++++++++++
net/ipv4/tcp.c | 26 ++++++++++----------------
3 files changed, 22 insertions(+), 16 deletions(-)
diff --git a/include/linux/socket.h b/include/linux/socket.h
index d18cc47e89bd0..c3322eb3d6865 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -392,6 +392,8 @@ struct ucred {
extern int move_addr_to_kernel(void __user *uaddr, int ulen, struct sockaddr_storage *kaddr);
extern int put_cmsg(struct msghdr*, int level, int type, int len, void *data);
+extern int put_cmsg_notrunc(struct msghdr *msg, int level, int type, int len,
+ void *data);
struct timespec64;
struct __kernel_timespec;
diff --git a/net/core/scm.c b/net/core/scm.c
index 4f6a14babe5ae..733c0cbd393d2 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -282,6 +282,16 @@ int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
}
EXPORT_SYMBOL(put_cmsg);
+int put_cmsg_notrunc(struct msghdr *msg, int level, int type, int len,
+ void *data)
+{
+ /* Don't produce truncated CMSGs */
+ if (!msg->msg_control || msg->msg_controllen < CMSG_LEN(len))
+ return -ETOOSMALL;
+
+ return put_cmsg(msg, level, type, len, data);
+}
+
void put_cmsg_scm_timestamping64(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
{
struct scm_timestamping64 tss;
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 68cb6a966b18b..b731a4a8f2b0d 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2456,14 +2456,12 @@ static int tcp_recvmsg_dmabuf(struct sock *sk, const struct sk_buff *skb,
*/
memset(&dmabuf_cmsg, 0, sizeof(dmabuf_cmsg));
dmabuf_cmsg.frag_size = copy;
- err = put_cmsg(msg, SOL_SOCKET, SO_DEVMEM_LINEAR,
- sizeof(dmabuf_cmsg), &dmabuf_cmsg);
- if (err || msg->msg_flags & MSG_CTRUNC) {
- msg->msg_flags &= ~MSG_CTRUNC;
- if (!err)
- err = -ETOOSMALL;
+ err = put_cmsg_notrunc(msg, SOL_SOCKET,
+ SO_DEVMEM_LINEAR,
+ sizeof(dmabuf_cmsg),
+ &dmabuf_cmsg);
+ if (err)
goto out;
- }
sent += copy;
@@ -2517,16 +2515,12 @@ static int tcp_recvmsg_dmabuf(struct sock *sk, const struct sk_buff *skb,
offset += copy;
remaining_len -= copy;
- err = put_cmsg(msg, SOL_SOCKET,
- SO_DEVMEM_DMABUF,
- sizeof(dmabuf_cmsg),
- &dmabuf_cmsg);
- if (err || msg->msg_flags & MSG_CTRUNC) {
- msg->msg_flags &= ~MSG_CTRUNC;
- if (!err)
- err = -ETOOSMALL;
+ err = put_cmsg_notrunc(msg, SOL_SOCKET,
+ SO_DEVMEM_DMABUF,
+ sizeof(dmabuf_cmsg),
+ &dmabuf_cmsg);
+ if (err)
goto out;
- }
atomic_long_inc(&niov->pp_ref_count);
tcp_xa_pool.netmems[tcp_xa_pool.idx++] = skb_frag_netmem(frag);
--
2.39.5
