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Message-ID: <20181129143855.GB14550@hmswarspite.think-freely.org>
Date: Thu, 29 Nov 2018 09:38:55 -0500
From: Neil Horman <nhorman@...driver.com>
To: Xin Long <lucien.xin@...il.com>
Cc: network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
davem@...emloft.net,
Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: Re: [PATCHv2 net] sctp: check and update stream->out_curr when
allocating stream_out
On Thu, Nov 29, 2018 at 02:42:56PM +0800, Xin Long wrote:
> Now when using stream reconfig to add out streams, stream->out
> will get re-allocated, and all old streams' information will
> be copied to the new ones and the old ones will be freed.
>
> So without stream->out_curr updated, next time when trying to
> send from stream->out_curr stream, a panic would be caused.
>
> This patch is to check and update stream->out_curr when
> allocating stream_out.
>
> v1->v2:
> - define fa_index() to get elem index from stream->out_curr.
>
> Fixes: 5bbbbe32a431 ("sctp: introduce stream scheduler foundations")
> Reported-by: Ying Xu <yinxu@...hat.com>
> Reported-by: syzbot+e33a3a138267ca119c7d@...kaller.appspotmail.com
> Signed-off-by: Xin Long <lucien.xin@...il.com>
> ---
> net/sctp/stream.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/net/sctp/stream.c b/net/sctp/stream.c
> index 3892e76..30e7809 100644
> --- a/net/sctp/stream.c
> +++ b/net/sctp/stream.c
> @@ -84,6 +84,19 @@ static void fa_zero(struct flex_array *fa, size_t index, size_t count)
> }
> }
>
> +static size_t fa_index(struct flex_array *fa, void *elem, size_t count)
> +{
> + size_t index = 0;
> +
> + while (count--) {
> + if (elem == flex_array_get(fa, index))
> + break;
> + index++;
> + }
> +
> + return index;
> +}
> +
> /* Migrates chunks from stream queues to new stream queues if needed,
> * but not across associations. Also, removes those chunks to streams
> * higher than the new max.
> @@ -147,6 +160,13 @@ static int sctp_stream_alloc_out(struct sctp_stream *stream, __u16 outcnt,
>
> if (stream->out) {
> fa_copy(out, stream->out, 0, min(outcnt, stream->outcnt));
> + if (stream->out_curr) {
> + size_t index = fa_index(stream->out, stream->out_curr,
> + stream->outcnt);
> +
> + BUG_ON(index == stream->outcnt);
> + stream->out_curr = flex_array_get(out, index);
> + }
> fa_free(stream->out);
> }
>
> --
> 2.1.0
>
>
This is the sort of thing I'm talking about. Its a little more code, but if you
augment the flex_array api like this, you can preform a resize operation on your
existing flex array, and you can avoid all the copying, and need to update
pointers maintained outside the array. Note this code isn't tested at all, but
its close to what I think should work.
diff --git a/include/linux/flex_array.h b/include/linux/flex_array.h
index b94fa61b51fb..7fa1f27a91b5 100644
--- a/include/linux/flex_array.h
+++ b/include/linux/flex_array.h
@@ -73,6 +73,8 @@ struct flex_array {
struct flex_array *flex_array_alloc(int element_size, unsigned int total,
gfp_t flags);
+struct flex_array *flex_array_resize(struct flex_array *fa, unsigned int total, gfp_t flags);
+
/**
* flex_array_prealloc() - Ensures that memory for the elements indexed in the
* range defined by start and nr_elements has been allocated.
diff --git a/lib/flex_array.c b/lib/flex_array.c
index 2eed22fa507c..f8d54af3891b 100644
--- a/lib/flex_array.c
+++ b/lib/flex_array.c
@@ -109,6 +109,7 @@ struct flex_array *flex_array_alloc(int element_size, unsigned int total,
ret->total_nr_elements = total;
ret->elems_per_part = elems_per_part;
ret->reciprocal_elems = reciprocal_elems;
+ ret->elements_used = 0;
if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
memset(&ret->parts[0], FLEX_ARRAY_FREE,
FLEX_ARRAY_BASE_BYTES_LEFT);
@@ -116,6 +117,53 @@ struct flex_array *flex_array_alloc(int element_size, unsigned int total,
}
EXPORT_SYMBOL(flex_array_alloc);
+static int flex_array_last_element_index(struct flex_array *fa)
+{
+ struct flex_array_part *part;
+ int part_nr;
+ int i,j;
+
+ if (elements_fit_in_base(fa)) {
+ part = (struct flex_array_part *)&fa->parts[0];
+ for (i = fa->elems_per_part; i >= 0; i--)
+ if (part->elements[i] != FLEX_ARRAY_FREE)
+ return i;
+ }
+
+ i = fa->total_nr_elements;
+ for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
+ part = fa->parts[part_nr];
+ if (!part) {
+ i -= fa->elems_per_part;
+ continue;
+ }
+ for (j = fa->elems_per_part; j >= 0; j--, i--)
+ if (part->elements[j] != FLEX_ARRAY_FREE)
+ goto out;
+ }
+out:
+ return i;
+}
+
+struct flex_array *flex_array_resize(struct flex_array *fa, unsigned int total, gfp_t flags)
+{
+ if (total >= fa->total_nr_elements) {
+ /* Grow case */
+ if (total > max_size)
+ return ERR_PTR(-ETOOBIG);
+ fa->total_nr_elements = total;
+ } else {
+ /* Shrink case */
+ /* Drop any pages we don't need*/
+ flex_array_shrink(fa);
+ if (flex_array_last_element_index(fa) >= total)
+ return ERR_PTR(-ESIZE);
+ fa->total_nr_elements = total;
+ }
+ return fa;
+}
+EXPORT_SYMBOL(flex_array_resize);
+
static int fa_element_to_part_nr(struct flex_array *fa,
unsigned int element_nr)
{
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