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SubjectRe: [kmemcheck] WARNING: kmemcheck: Caught 32-bit read from uninitialized memory, in sock_init_data()

* Eric Dumazet <eric.dumazet@gmail.com> wrote:

> Vegard Nossum a ??crit :
> > 2009/8/26 Ingo Molnar <mingo@elte.hu>:
> >> -tip testing found another kmemcheck warning:
> >>
> >> calling netlink_proto_init+0x0/0x1b0 @ 1
> >> NET: Registered protocol family 16
> >> initcall netlink_proto_init+0x0/0x1b0 returned 0 after 39062 usecs
> >> calling olpc_init+0x0/0x110 @ 1
> >> WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f5c38304)
> >> 0100000002000000000000000000000000000000ad4eaddeffffffffffffffff
> >> i i i i i i u u i i i i i i i i i i i i i i i i i i i i i i i i
> >> ^
> >>
> >> Pid: 1, comm: swapper Not tainted (2.6.31-rc7-tip-01170-gaaea9cf-dirty #24) P4DC6
> >> EIP: 0060:[<c15c8ab1>] EFLAGS: 00010286 CPU: 0
> >> EIP is at sock_init_data+0xe1/0x220
> >> EAX: 0001b000 EBX: f606196c ECX: 00000000 EDX: c1a148d2
> >> ESI: f6061800 EDI: f5c38300 EBP: f606ef0c ESP: c1ceb9ac
> >> DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
> >> CR0: 8005003b CR2: f60a8108 CR3: 01a61000 CR4: 000006f0
> >> DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
> >> DR6: ffff4ff0 DR7: 00000400
> >> [<c15fac15>] __netlink_create+0x35/0xa0
> >> [<c15fd01a>] netlink_kernel_create+0x5a/0x180
> >> [<c15df55e>] rtnetlink_net_init+0x1e/0x50
> >> [<c15d130a>] register_pernet_operations+0x6a/0xf0
> >> [<c15d14fe>] register_pernet_subsys+0x1e/0x30
> >> [<c1b3d84c>] rtnetlink_init+0x4c/0x100
> >> [<c1b3e105>] netlink_proto_init+0x105/0x1b0
> >> [<c1001037>] do_one_initcall+0x27/0x170
> >> [<c1afea97>] kernel_init+0x157/0x210
> >> [<c10039a7>] kernel_thread_helper+0x7/0x10
> >> [<ffffffff>] 0xffffffff
> >> initcall olpc_init+0x0/0x110 returned 0 after 0 usecs
> >> calling bdi_class_init+0x0/0x40 @ 1
> >>
> >> config attached.
> >
> > Thanks. AFAICT, it's this one:
> >
> > 1816 void sock_init_data(struct socket *sock, struct sock *sk)
> > 1817 {
> > ...
> > 1835 sock_set_flag(sk, SOCK_ZAPPED);
>
> Are you sure it is not the 16 bit padding in 'struct sock', after 'type' field ?
>
> struct socket {
> socket_state state;
> short type;
> // here, a 16 bits hole
> unsigned long flags;
>
> the warning is strange since I suspect it happens here :
>
> if (sock) {
> <<>> sk->sk_type = sock->type; // here, kmemcheck warning while reading sock->type
> sk->sk_sleep = &sock->wait;
> sock->sk = sk;
>
> and sock->type is a 16 bit field, correctly initialized (with value = 2)
> (Yes the hole, right after, is not initialized)
>
> WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f5c38304)
> 0100000002000000000000000000000000000000ad4eaddeffffffffffffffff
> i i i i i i u u i i i i i i i i i i i i i i i i i i i i i i i i

if so then we could perhaps annotate that by initializing it to zero
on kmemcheck only. (or initialize it unconditionally if possible -
that's generally the cleanest, 16-bit accesses arent cheap on all
platforms)

Ingo


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