On Fri, Sep 01, 2017 at 12:15:17PM +0300, Stanislav Kinsburskiy wrote: > 31.08.2017 20:22, Dmitry V. Levin пишет: > > On Thu, Aug 31, 2017 at 05:57:11PM +0400, Stanislav Kinsburskiy wrote: > >> The structure autofs_v5_packet (except name) is not aligned by 8 bytes, > >> which > >> lead to different sizes in 32 and 64-bit architectures. > >> Let's form 32-bit compatible packet when daemon has 32-bit addressation. > >> > >> Signed-off-by: Stanislav Kinsburskiy <skinsbur...@virtuozzo.com> > >> --- > >> fs/autofs4/waitq.c | 11 +++++++++-- > >> 1 file changed, 9 insertions(+), 2 deletions(-) > >> > >> diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c > >> index 309ca6b..484cf2e 100644 > >> --- a/fs/autofs4/waitq.c > >> +++ b/fs/autofs4/waitq.c > >> @@ -153,12 +153,19 @@ static void autofs4_notify_daemon(struct > >> autofs_sb_info *sbi, > >> { > >> struct autofs_v5_packet *packet = &pkt.v5_pkt.v5_packet; > >> struct user_namespace *user_ns = sbi->pipe->f_cred->user_ns; > >> + size_t name_offset; > >> > >> - pktsz = sizeof(*packet); > >> + if (sbi->is32bit) > >> + name_offset = offsetof(struct autofs_v5_packet, len) + > >> + sizeof(packet->len); > >> + else > >> + name_offset = offsetof(struct autofs_v5_packet, name); > > > > This doesn't help at all because the offset of struct autofs_v5_packet.name > > does not change. > > > >> + pktsz = name_offset + sizeof(packet->name); > > > > What changes is pktsz: it's either sizeof(struct autofs_v5_packet) > > or 4 bytes less, depending on the architecture. > > Indeed. Thanks! > > > For example, > > > > #ifdef CONFIG_COMPAT > > if (__alignof__(compat_u64) < __alignof__(u64) && sbi->is32bit) > > Unfortunately I don't get this "alignof" checks. > The intention of "is32bit" was to define this compat case completely. > Why are they required?
On some 32-bit architectures like arm, u64 is 64-bit aligned, on others like x86 it is not. This alignof check ensures that compat 32-bit architectures with 64-bit alignment are not going to be broken by the change. -- ldv
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