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SubjectRe: [PATCH v3] net: sock: move ->sk_shutdown out of bitfields.
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On Wed, 2016-05-18 at 17:36 +0300, Andrey Ryabinin wrote:
> ->sk_shutdown bits share one bitfield with some other bits in sock struct,
> such as ->sk_no_check_[r,t]x, ->sk_userlocks ...
> sock_setsockopt() may write to these bits, while holding the socket lock.
>
> In case of AF_UNIX sockets, we change ->sk_shutdown bits while holding only
> unix_state_lock(). So concurrent setsockopt() and shutdown() may lead
> to corrupting these bits.
>
> Fix this by moving ->sk_shutdown bits out of bitfield into a separate byte.
> This will not change the 'struct sock' size since ->sk_shutdown moved into
> previously unused 16-bit hole.
>
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Suggested-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
> ---
>
> Changes since v1:
> - move sk_shutdown into a separate byte instead of locking
> AF_UNIX sockets.
>
> Changes since v2:
> - reorder bitfields, so that sk_type/sk_protocol still fit in
> separate 2-bytes/byte.
>

I suggested to use an explicit padding, to clearly show that two bits
are available there. You also could add a comment to remind the rules.

Something like :

diff --git a/include/net/sock.h b/include/net/sock.h
index c9c8b19df27c558354687119db60c0716909ea3f..4e239a7ef4f67b1988fe119d81566d1465a2b596 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -382,8 +382,10 @@ struct sock {
atomic_t sk_omem_alloc;
int sk_sndbuf;
struct sk_buff_head sk_write_queue;
+
+ /* because of non atomicity rules, all changes are protected by socket lock */
kmemcheck_bitfield_begin(flags);
- unsigned int sk_shutdown : 2,
+ unsigned int sk_padding : 2,
sk_no_check_tx : 1,
sk_no_check_rx : 1,
sk_userlocks : 4,
@@ -391,6 +393,7 @@ struct sock {
sk_type : 16;
#define SK_PROTOCOL_MAX U8_MAX
kmemcheck_bitfield_end(flags);
+
int sk_wmem_queued;
gfp_t sk_allocation;
u32 sk_pacing_rate; /* bytes per second */
@@ -418,6 +421,7 @@ struct sock {
struct timer_list sk_timer;
ktime_t sk_stamp;
u16 sk_tsflags;
+ u8 sk_shutdown;
u32 sk_tskey;
struct socket *sk_socket;
void *sk_user_data;

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