ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 109 insertions, 0 deletions

diff --git a/Documentation/networking/tproxy.rst b/Documentation/networking/tproxy.rst
new file mode 100644
index 000000000..75e4990cc
--- /dev/null
+++ b/Documentation/networking/tproxy.rst
@@ -0,0 +1,109 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=========================
+Transparent proxy support
+=========================
+
+This feature adds Linux 2.2-like transparent proxy support to current kernels.
+To use it, enable the socket match and the TPROXY target in your kernel config.
+You will need policy routing too, so be sure to enable that as well.
+
+From Linux 4.18 transparent proxy support is also available in nf_tables.
+
+1. Making non-local sockets work
+================================
+
+The idea is that you identify packets with destination address matching a local
+socket on your box, set the packet mark to a certain value::
+
+    # iptables -t mangle -N DIVERT
+    # iptables -t mangle -A PREROUTING -p tcp -m socket --transparent -j DIVERT
+    # iptables -t mangle -A DIVERT -j MARK --set-mark 1
+    # iptables -t mangle -A DIVERT -j ACCEPT
+
+Alternatively you can do this in nft with the following commands::
+
+    # nft add table filter
+    # nft add chain filter divert "{ type filter hook prerouting priority -150; }"
+    # nft add rule filter divert meta l4proto tcp socket transparent 1 meta mark set 1 accept
+
+And then match on that value using policy routing to have those packets
+delivered locally::
+
+    # ip rule add fwmark 1 lookup 100
+    # ip route add local 0.0.0.0/0 dev lo table 100
+
+Because of certain restrictions in the IPv4 routing output code you'll have to
+modify your application to allow it to send datagrams _from_ non-local IP
+addresses. All you have to do is enable the (SOL_IP, IP_TRANSPARENT) socket
+option before calling bind::
+
+    fd = socket(AF_INET, SOCK_STREAM, 0);
+    /* - 8< -*/
+    int value = 1;
+    setsockopt(fd, SOL_IP, IP_TRANSPARENT, &value, sizeof(value));
+    /* - 8< -*/
+    name.sin_family = AF_INET;
+    name.sin_port = htons(0xCAFE);
+    name.sin_addr.s_addr = htonl(0xDEADBEEF);
+    bind(fd, &name, sizeof(name));
+
+A trivial patch for netcat is available here:
+http://people.netfilter.org/hidden/tproxy/netcat-ip_transparent-support.patch
+
+
+2. Redirecting traffic
+======================
+
+Transparent proxying often involves "intercepting" traffic on a router. This is
+usually done with the iptables REDIRECT target; however, there are serious
+limitations of that method. One of the major issues is that it actually
+modifies the packets to change the destination address -- which might not be
+acceptable in certain situations. (Think of proxying UDP for example: you won't
+be able to find out the original destination address. Even in case of TCP
+getting the original destination address is racy.)
+
+The 'TPROXY' target provides similar functionality without relying on NAT. Simply
+add rules like this to the iptables ruleset above::
+
+    # iptables -t mangle -A PREROUTING -p tcp --dport 80 -j TPROXY \
+      --tproxy-mark 0x1/0x1 --on-port 50080
+
+Or the following rule to nft::
+
+    # nft add rule filter divert tcp dport 80 tproxy to :50080 meta mark set 1 accept
+
+Note that for this to work you'll have to modify the proxy to enable (SOL_IP,
+IP_TRANSPARENT) for the listening socket.
+
+As an example implementation, tcprdr is available here:
+https://git.breakpoint.cc/cgit/fw/tcprdr.git/
+This tool is written by Florian Westphal and it was used for testing during the
+nf_tables implementation.
+
+3. Iptables and nf_tables extensions
+====================================
+
+To use tproxy you'll need to have the following modules compiled for iptables:
+
+ - NETFILTER_XT_MATCH_SOCKET
+ - NETFILTER_XT_TARGET_TPROXY
+
+Or the floowing modules for nf_tables:
+
+ - NFT_SOCKET
+ - NFT_TPROXY
+
+4. Application support
+======================
+
+4.1. Squid
+----------
+
+Squid 3.HEAD has support built-in. To use it, pass
+'--enable-linux-netfilter' to configure and set the 'tproxy' option on
+the HTTP listener you redirect traffic to with the TPROXY iptables
+target.
+
+For more information please consult the following page on the Squid
+wiki: http://wiki.squid-cache.org/Features/Tproxy4