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From badb16c481cf592a1761ad20dd0a84614d2bbd5b Mon Sep 17 00:00:00 2001
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From: David Rheinsberg <david.rheinsberg@gmail.com>
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Date: Thu, 14 Mar 2019 13:33:28 +0100
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Subject: [PATCH] sd-bus: fix SASL reply to empty AUTH
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The correct way to reply to "AUTH <protocol>" without any payload is to
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send "DATA" rather than "OK". The "DATA" reply triggers the client to
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respond with the requested payload.
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In fact, adding the data as hex-encoded argument like
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"AUTH <protocol> <hex-data>" is an optimization that skips the "DATA"
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roundtrip. The standard way to perform an authentication is to send the
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"DATA" line.
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This commit fixes sd-bus to properly send the "DATA" line. Surprisingly
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no existing implementation depends on this, as they all pass the data
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directly as argument to "AUTH". This will not work if we want to pass
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an empty argument, though.
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Signed-off-by: David Rheinsberg <david.rheinsberg@gmail.com>
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(cherry picked from commit 2010873b4b49b223e0cc07d28205b09c693ef005)
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Related: #1838081
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---
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 src/libsystemd/sd-bus/bus-socket.c | 10 ++++++++--
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 1 file changed, 8 insertions(+), 2 deletions(-)
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diff --git a/src/libsystemd/sd-bus/bus-socket.c b/src/libsystemd/sd-bus/bus-socket.c
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index 1c8b331b48..e505d43c6b 100644
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--- a/src/libsystemd/sd-bus/bus-socket.c
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+++ b/src/libsystemd/sd-bus/bus-socket.c
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@@ -399,7 +399,10 @@ static int bus_socket_auth_verify_server(sd_bus *b) {
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                                 r = bus_socket_auth_write(b, "REJECTED\r\n");
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                         else {
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                                 b->auth = BUS_AUTH_ANONYMOUS;
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-                                r = bus_socket_auth_write_ok(b);
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+                                if (l <= strlen("AUTH ANONYMOUS"))
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+                                        r = bus_socket_auth_write(b, "DATA\r\n");
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+                                else
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+                                        r = bus_socket_auth_write_ok(b);
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                         }
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                 } else if (line_begins(line, l, "AUTH EXTERNAL")) {
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@@ -413,7 +416,10 @@ static int bus_socket_auth_verify_server(sd_bus *b) {
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                                 r = bus_socket_auth_write(b, "REJECTED\r\n");
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                         else {
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                                 b->auth = BUS_AUTH_EXTERNAL;
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-                                r = bus_socket_auth_write_ok(b);
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+                                if (l <= strlen("AUTH EXTERNAL"))
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+                                        r = bus_socket_auth_write(b, "DATA\r\n");
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+                                else
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+                                        r = bus_socket_auth_write_ok(b);
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                         }
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                 } else if (line_begins(line, l, "AUTH"))