[PATCH net] sctp: trim optlen when it's a huge value in sctp_setsockopt

[PATCH net] sctp: trim optlen when it's a huge value in sctp_setsockopt

[Xin Long]

After commit ca84bd058dae ("sctp: copy the optval from user space in
sctp_setsockopt"), it does memory allocation in sctp_setsockopt with
the optlen, and it would fail the allocation and return error if the
optlen from user space is a huge value.

This breaks some sockopts, like SCTP_HMAC_IDENT, SCTP_RESET_STREAMS and
SCTP_AUTH_KEY, as when processing these sockopts before, optlen would
be trimmed to a biggest value it needs when optlen is a huge value,
instead of failing the allocation and returning error.

This patch is to fix the allocation failure when it's a huge optlen from
user space by trimming it to the biggest size sctp sockopt may need when
necessary, and this biggest size is from sctp_setsockopt_reset_streams()
for SCTP_RESET_STREAMS, which is bigger than those for SCTP_HMAC_IDENT
and SCTP_AUTH_KEY.

Fixes: ca84bd058dae ("sctp: copy the optval from user space in sctp_setsockopt")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 net/sctp/socket.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index e64e01f61b11..6b937bfd4751 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -4577,6 +4577,10 @@ static int sctp_setsockopt(struct sock *sk, int level, int optname,
 	}
 
 	if (optlen > 0) {
+		/* Trim it to the biggest size sctp sockopt may need if necessary */
+		optlen = min_t(unsigned int, optlen,
+			       PAGE_ALIGN(USHRT_MAX +
+					  sizeof(__u16) * sizeof(struct sctp_reset_streams)));
 		kopt = memdup_sockptr(optval, optlen);
 		if (IS_ERR(kopt))
 			return PTR_ERR(kopt);
-- 
2.27.0

Re: [PATCH net] sctp: trim optlen when it's a huge value in sctp_setsockopt

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Sat, 17 Jul 2021 17:19:19 -0400 you wrote:
> After commit ca84bd058dae ("sctp: copy the optval from user space in
> sctp_setsockopt"), it does memory allocation in sctp_setsockopt with
> the optlen, and it would fail the allocation and return error if the
> optlen from user space is a huge value.
> 
> This breaks some sockopts, like SCTP_HMAC_IDENT, SCTP_RESET_STREAMS and
> SCTP_AUTH_KEY, as when processing these sockopts before, optlen would
> be trimmed to a biggest value it needs when optlen is a huge value,
> instead of failing the allocation and returning error.
> 
> [...]

Here is the summary with links:
  - [net] sctp: trim optlen when it's a huge value in sctp_setsockopt
    https://git.kernel.org/netdev/net/c/2f3fdd8d4805

You are awesome, thank you!
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