My hypothesis:
On these architectures, struct gu_rse (defined at
galerautils/src/gu_rand.c:19) has holes in it due to alignment. In
function gu_rand_seed_long(galerautils/src/gu_rand.c:30), a struct of
this type is initialised on a by-member basis. But its address is then
passed to gu_fast_hash64_medium which reads it as a buffer. So any holes
in that buffer remain uninitialized.
I presume that powerpc and armhf are the architectures where struct
gu_rse end up with holes in it, and the other architectures do not.
However, gcc is free to change this in the future, so I think this bug
applies to all architectures, and a proper fix would not be
architecture-specific.
Applying the following patch fixes the issue and so is consistent with
my hypothesis:
--- percona-galera-3-3.8-3390.orig/galerautils/src/gu_rand.c
+++ percona-galera-3-3.8-3390/galerautils/src/gu_rand.c
@@ -16,7 +16,7 @@
/*! Structure to hold entropy data.
* Should be at least 20 bytes on 32-bit systems and 28 bytes on 64-bit */
-struct gu_rse
+struct __attribute__((__packed__)) gu_rse
{
long long time;
const void* heap_ptr;
It would seem cleaner to me to memset(&rse, 0, sizeof(rse)) though. gcc
would probably optimise the initialization fully, leaving architectures
without the holes unchanged.
Can I have some feedback from upstream on this though please? Is this
code being used for anything that needs to be cryptographically secure?
Will you accept a memset fix, and will this have any unintended side-
effects?
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https://bugs.launchpad.net/bugs/1430874
Title:
FTBFS on powerpc and armhf due to uninitialized struct
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