From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Horman Subject: Re: [PATCHv2 net] sctp: check and update stream->out_curr when allocating stream_out Date: Fri, 30 Nov 2018 07:20:18 -0500 Message-ID: <20181130122018.GA24285@hmswarspite.think-freely.org> References: <8a5df8eb5cc41dfc3d08e294147b9729bbe90aa0.1543473776.git.lucien.xin@gmail.com> <20181129143855.GB14550@hmswarspite.think-freely.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: network dev , linux-sctp@vger.kernel.org, davem , Marcelo Ricardo Leitner To: Xin Long Return-path: Received: from charlotte.tuxdriver.com ([70.61.120.58]:51826 "EHLO smtp.tuxdriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726549AbeK3XaH (ORCPT ); Fri, 30 Nov 2018 18:30:07 -0500 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Fri, Nov 30, 2018 at 03:22:39PM +0900, Xin Long wrote: > On Thu, Nov 29, 2018 at 11:39 PM Neil Horman wrote: > > > > 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 > > > Reported-by: syzbot+e33a3a138267ca119c7d@syzkaller.appspotmail.com > > > Signed-off-by: Xin Long > > > --- > > > 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) > > { > I have a question about how it checks one part is free in > flex_array_shrink(): > part_is_free() is doing it by checking: > if (part->elements[all] == FLEX_ARRAY_FREE) ... > > What if the data in the array that users put is FLEX_ARRAY_FREE, > it will be treated as free, but in fact it's still in use? > I noticed that too, I think they're taking an unsafe shortcut honestly, assuming that the FLEX_ARRAY_FREE poison value in the first byte is indicative of the entire part being free. For this use case its not likely a problem, because the first element of the stream is a pointer, and so its unlikely to start with the FLEX_ARRAY_FREE value, but it could suffer from aliasing in other cases. In the current design they should really be doing a memory comparison of the entire object length to a buffer filled with the poison value to determine free status. I would suggest not worrying about it for the purposes of this patch, but I think I'll write a fix for the flex_array code that adds a byte to the head of whatever object is bing stored to be reserved for free / in-use indicators. Neil From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Horman Date: Fri, 30 Nov 2018 12:20:18 +0000 Subject: Re: [PATCHv2 net] sctp: check and update stream->out_curr when allocating stream_out Message-Id: <20181130122018.GA24285@hmswarspite.think-freely.org> List-Id: References: <8a5df8eb5cc41dfc3d08e294147b9729bbe90aa0.1543473776.git.lucien.xin@gmail.com> <20181129143855.GB14550@hmswarspite.think-freely.org> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Xin Long Cc: network dev , linux-sctp@vger.kernel.org, davem , Marcelo Ricardo Leitner On Fri, Nov 30, 2018 at 03:22:39PM +0900, Xin Long wrote: > On Thu, Nov 29, 2018 at 11:39 PM Neil Horman wrote: > > > > 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 > > > Reported-by: syzbot+e33a3a138267ca119c7d@syzkaller.appspotmail.com > > > Signed-off-by: Xin Long > > > --- > > > 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) > > { > I have a question about how it checks one part is free in > flex_array_shrink(): > part_is_free() is doing it by checking: > if (part->elements[all] = FLEX_ARRAY_FREE) ... > > What if the data in the array that users put is FLEX_ARRAY_FREE, > it will be treated as free, but in fact it's still in use? > I noticed that too, I think they're taking an unsafe shortcut honestly, assuming that the FLEX_ARRAY_FREE poison value in the first byte is indicative of the entire part being free. For this use case its not likely a problem, because the first element of the stream is a pointer, and so its unlikely to start with the FLEX_ARRAY_FREE value, but it could suffer from aliasing in other cases. In the current design they should really be doing a memory comparison of the entire object length to a buffer filled with the poison value to determine free status. I would suggest not worrying about it for the purposes of this patch, but I think I'll write a fix for the flex_array code that adds a byte to the head of whatever object is bing stored to be reserved for free / in-use indicators. Neil