From 443a55981388f519fb6528a8ee042f9e69079b68 Mon Sep 17 00:00:00 2001 From: David Herrmann Date: Thu, 16 Jul 2015 11:00:55 +0200 Subject: sd-bus: fix gvariant structure encoding In gvariant, all fixed-size objects need to be sized a multiple of their alignment. If a structure has only fixed-size members, it is required to be fixed size itself. If you imagine a structure like (ty), you have an 8-byte member followed by an 1-byte member. Hence, the overall inner-size is 9. The alignment of the object is 8, though. Therefore, the specs mandates final padding after fixed-size structures, to make sure it's sized a multiple of its alignment (=> 16). On the gvariant decoder side, we already account for this in bus_gvariant_get_size(), as we apply overall padding to the size of the structure. Therefore, our decoder correctly skips such final padding when parsing fixed-size structure. On the gvariant encoder side, however, we don't account for this final padding. This patch fixes the structure and dict-entry encoders to properly place such padding at the end of non-uniform fixed-size structures. The problem can be easily seen by running: $ busctl --user monitor and $ busctl call --user org.freedesktop.systemd1 / org.foobar foobar "(ty)" 777 8 The monitor will fail to parse the message and print an error. With this patch applied, everything works fine again. This patch also adds a bunch of test-cases to force non-uniform structures with non-pre-aligned positions. Thanks to Jan Alexander Steffens for spotting this and narrowing it down to non-uniform gvariant structures. Fixes #597. --- src/libsystemd/sd-bus/bus-message.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) (limited to 'src/libsystemd/sd-bus/bus-message.c') diff --git a/src/libsystemd/sd-bus/bus-message.c b/src/libsystemd/sd-bus/bus-message.c index 983e2f62cd..18685be8ff 100644 --- a/src/libsystemd/sd-bus/bus-message.c +++ b/src/libsystemd/sd-bus/bus-message.c @@ -2161,6 +2161,7 @@ static int bus_message_close_variant(sd_bus_message *m, struct bus_container *c) } static int bus_message_close_struct(sd_bus_message *m, struct bus_container *c, bool add_offset) { + bool fixed_size = true; size_t n_variable = 0; unsigned i = 0; const char *p; @@ -2196,6 +2197,8 @@ static int bus_message_close_struct(sd_bus_message *m, struct bus_container *c, /* We need to add an offset for each item that has a * variable size and that is not the last one in the * list */ + if (r == 0) + fixed_size = false; if (r == 0 && p[n] != 0) n_variable++; @@ -2207,7 +2210,19 @@ static int bus_message_close_struct(sd_bus_message *m, struct bus_container *c, assert(c->need_offsets || n_variable == 0); if (n_variable <= 0) { - a = message_extend_body(m, 1, 0, add_offset, false); + int alignment = 1; + + /* Structures with fixed-size members only have to be + * fixed-size themselves. But gvariant requires all fixed-size + * elements to be sized a multiple of their alignment. Hence, + * we must *always* add final padding after the last member so + * the overall size of the structure is properly aligned. */ + if (fixed_size) + alignment = bus_gvariant_get_alignment(strempty(c->signature)); + + assert(alignment > 0); + + a = message_extend_body(m, alignment, 0, add_offset, false); if (!a) return -ENOMEM; } else { -- cgit v1.2.3-54-g00ecf