On Thu, Aug 31, 2017 at 01:48:27PM +0300, Stanislav Kinsburskiy wrote: > > > 31.08.2017 13:38, Dmitry V. Levin пишет: > > On Thu, Aug 31, 2017 at 02:11:34PM +0400, Stanislav Kinsburskiy wrote: > >> Due to integer variables alignment size of struct autofs_v5_packet in 300 > >> bytes in 32-bit architectures (instead of 304 bytes in 64-bits > >> architectures). > >> > >> This may lead to memory corruption (64 bits kernel always send 304 bytes, > >> while 32-bit userspace application expects for 300). > >> > >> https://jira.sw.ru/browse/PSBM-71078 > >> > >> Signed-off-by: Stanislav Kinsburskiy <skinsbur...@virtuozzo.com> > >> --- > >> include/uapi/linux/auto_fs4.h | 2 ++ > >> 1 file changed, 2 insertions(+) > >> > >> diff --git a/include/uapi/linux/auto_fs4.h b/include/uapi/linux/auto_fs4.h > >> index e02982f..8729a47 100644 > >> --- a/include/uapi/linux/auto_fs4.h > >> +++ b/include/uapi/linux/auto_fs4.h > >> @@ -137,6 +137,8 @@ struct autofs_v5_packet { > >> __u32 pid; > >> __u32 tgid; > >> __u32 len; > >> + __u32 blob; /* This is needed to align structure up to 8 > >> + bytes for ALL archs including 32-bit */ > >> char name[NAME_MAX+1]; > >> }; > > > > This change breaks ABI because it changes offsetof(struct autofs_v5_packet, > > name). > > If you need to fix the alignment, use __attribute__((aligned(8))). > > > > Nice to know you're watching. > Yes, attribute is better. > But how ABI is broken? On x86_64 this alignment is implied, so nothing is > changed.
Your change increases offsetof(struct autofs_v5_packet, name) by 4 on all architectures. On architectures where the structure is 32-bit aligned this also leads to increase of its size by 4. > > An alignment change would also be an ABI breakage on 32-bit architectures, > > though. > > > > True. > But from my POW better have it working on 64bit archs for 32bit apps. > But anyway, upstream guys will device, whether they want 32-bit autofs > applications properly work on 64 or 32 bits. Let's fix old bugs without introducing new bugs. The right fix here seems to be a compat structure, that is, both 64-bit and 32-bit kernels should send the same 32-bit aligned structure, and it has to be the same structure sent by traditional 32-bit kernels. -- ldv
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