Re: [PATCH] net: recvmsg: Unconditionally zero struct sockaddr_storage
From: Eric Dumazet <hidden>
Date: 2017-10-31 17:31:39
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On Tue, 2017-10-31 at 09:14 -0700, Kees Cook wrote:
quoted hunk ↗ jump to hunk
Some protocols do not correctly wipe the contents of the on-stack struct sockaddr_storage sent down into recvmsg() (e.g. SCTP), and leak kernel stack contents to userspace. This wipes it unconditionally before per-protocol handlers run. Note that leaks like this are mitigated by building with CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL=y Reported-by: Alexander Potapenko <glider@google.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: netdev@vger.kernel.org Signed-off-by: Kees Cook <redacted> --- net/socket.c | 1 + 1 file changed, 1 insertion(+)diff --git a/net/socket.c b/net/socket.c index c729625eb5d3..34183f4fbdf8 100644 --- a/net/socket.c +++ b/net/socket.c@@ -2188,6 +2188,7 @@ static int ___sys_recvmsg(struct socket *sock, struct user_msghdr __user *msg, struct sockaddr __user *uaddr; int __user *uaddr_len = COMPAT_NAMELEN(msg); + memset(&addr, 0, sizeof(addr)); msg_sys->msg_name = &addr;
This kind of patch comes every year. Standard answer is : We fix the buggy protocol, we do not make everything slower just because we are lazy. struct sockaddr is 128 bytes, but IPV4 only uses a fraction of it. Also memset() is using long word stores, so next 4-byte or 2-byte stores on same location hit a performance problem on x86. By adding all these defensive programming, we would give strong incentives to bypass the kernel for networking. That would be bad.