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sock: Use unsafe_memcpy() for sock_copy()

PATCH Applied Kees Cook 3 participants 3 messages Mar 4, 2024 – Mar 6, 2024

Subsystems (4)
Networking Network drivers TCP Sockets
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Kees Cook

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#0 lore raw

PATCH v3 1/1 sock: Use unsafe_memcpy() for sock_copy()

While testing for places where zero-sized destinations were still showing up in the kernel, sock_copy() and inet_reqsk_clone() were found, which are using very specific memcpy() offsets for both avoiding a portion of struct sock, and copying beyond the end of it (since struct sock is really just a common header before the protocol-specific allocation). Instead of trying to unravel this historical lack of container_of(), just switch to unsafe_memcpy(), since that's effectively what was happening already (memcpy() wasn't checking 0-sized destinations while the code base was being converted away from fake flexible arrays).

Avoid the following false positive warning with future changes to CONFIG_FORTIFY_SOURCE:

memcpy: detected field-spanning write (size 3068) of destination "&nsk->__sk_common.skc_dontcopy_end" at net/core/sock.c:2057 (size 0)

Signed-off-by Kees Cook <[email protected]>

---
Cc: Jakub Kicinski <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Paolo Abeni <[email protected]>
Cc: [email protected]
v3: fix inet_reqsk_clone() comment
v2: https://lore.kernel.org/lkml/[email protected]
v1: https://lore.kernel.org/lkml/[email protected]

---
 net/core/sock.c                 | 5 +++--
 net/ipv4/inet_connection_sock.c | 5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)
net/core/sock.c +3 -2
index 0a7f46c37f0c..b7ea358eb18f 100644
@@ -2053,8 +2053,9 @@ static void sock_copy(struct sock *nsk, const struct sock *osk)
 
 	memcpy(nsk, osk, offsetof(struct sock, sk_dontcopy_begin));
 
-	memcpy(&nsk->sk_dontcopy_end, &osk->sk_dontcopy_end,
-	       prot->obj_size - offsetof(struct sock, sk_dontcopy_end));
+	unsafe_memcpy(&nsk->sk_dontcopy_end, &osk->sk_dontcopy_end,
+		      prot->obj_size - offsetof(struct sock, sk_dontcopy_end),
+		      /* alloc is larger than struct, see sk_prot_alloc() */);
 
 #ifdef CONFIG_SECURITY_NETWORK
 	nsk->sk_security = sptr;
net/ipv4/inet_connection_sock.c +3 -2
index 459af1f89739..6a14a44aa161 100644
@@ -906,8 +906,9 @@ static struct request_sock *inet_reqsk_clone(struct request_sock *req,
 
 	memcpy(nreq_sk, req_sk,
 	       offsetof(struct sock, sk_dontcopy_begin));
-	memcpy(&nreq_sk->sk_dontcopy_end, &req_sk->sk_dontcopy_end,
-	       req->rsk_ops->obj_size - offsetof(struct sock, sk_dontcopy_end));
+	unsafe_memcpy(&nreq_sk->sk_dontcopy_end, &req_sk->sk_dontcopy_end,
+		      req->rsk_ops->obj_size - offsetof(struct sock, sk_dontcopy_end),
+		      /* alloc is larger than struct, see above */);
 
 	sk_node_init(&nreq_sk->sk_node);
 	nreq_sk->sk_tx_queue_mapping = req_sk->sk_tx_queue_mapping;
Signature · 1 line
2.34.1
reviewer Reviewed-by on v3 1/1
#1 lore raw
Quoted 16 lines · Kees Cook

While testing for places where zero-sized destinations were still showing up in the kernel, sock_copy() and inet_reqsk_clone() were found, which are using very specific memcpy() offsets for both avoiding a portion of struct sock, and copying beyond the end of it (since struct sock is really just a common header before the protocol-specific allocation). Instead of trying to unravel this historical lack of container_of(), just switch to unsafe_memcpy(), since that's effectively what was happening already (memcpy() wasn't checking 0-sized destinations while the code base was being converted away from fake flexible arrays).

Avoid the following false positive warning with future changes to CONFIG_FORTIFY_SOURCE:

memcpy: detected field-spanning write (size 3068) of destination "&nsk->__sk_common.skc_dontcopy_end" at net/core/sock.c:2057 (size 0)

Signed-off-by Kees Cook <[email protected]>
Quoted 9 lines

---
Cc: Jakub Kicinski <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Paolo Abeni <[email protected]>
Cc: [email protected]
v3: fix inet_reqsk_clone() comment
v2: https://lore.kernel.org/lkml/[email protected]
v1: https://lore.kernel.org/lkml/[email protected]

Reviewed-by Simon Horman <[email protected]>
CI Applied
#2 lore raw
In reply to Kees Cook
This patch was applied to netdev/net-next.git (main) by Jakub Kicinski <[email protected]>:

Hello:

This patch was applied to netdev/net-next.git (main) by Jakub Kicinski <[email protected]>:

Quoted 11 lines · On Mon, 4 Mar 2024 13:29:31 -0800 you wrote:

While testing for places where zero-sized destinations were still showing up in the kernel, sock_copy() and inet_reqsk_clone() were found, which are using very specific memcpy() offsets for both avoiding a portion of struct sock, and copying beyond the end of it (since struct sock is really just a common header before the protocol-specific allocation). Instead of trying to unravel this historical lack of container_of(), just switch to unsafe_memcpy(), since that's effectively what was happening already (memcpy() wasn't checking 0-sized destinations while the code base was being converted away from fake flexible arrays).

[...]

Here is the summary with links:
- [v3] sock: Use unsafe_memcpy() for sock_copy()

    https://git.kernel.org/netdev/net-next/c/ff73f8344e58

You are awesome, thank you!

Signature · 2 lines
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