[PATCH v3 21/55] crypto: af_alg: Pin pages rather than ref'ing if appropriate

David Howells
2023-03-31T16:13:24Z

Convert AF_ALG to use iov_iter_extract_pages() instead of
iov_iter_get_pages(). This will pin pages or leave them unaltered rather
than getting a ref on them as appropriate to the iterator.

The pages need to be pinned for DIO-read rather than having refs taken on
them to prevent VM copy-on-write from malfunctioning during a concurrent
fork() (the result of the I/O would otherwise end up only visible to the
child process and not the parent).

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Herbert Xu <herbert@gondor.apana.org.au>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
cc: linux-crypto@vger.kernel.org
cc: netdev@vger.kernel.org
---
crypto/af_alg.c | 10 +++++++---
include/crypto/if_alg.h | 1 +
2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index 5f7252a5b7b4..7caff10df643 100644
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -533,14 +533,17 @@ static const struct net_proto_family alg_family = {

int af_alg_make_sg(struct af_alg_sgl *sgl, struct iov_iter *iter, int len)
{
+ struct page **pages = sgl->pages;
size_t off;
ssize_t n;
int npages, i;

- n = iov_iter_get_pages2(iter, sgl->pages, len, ALG_MAX_PAGES, &off);
+ n = iov_iter_extract_pages(iter, &pages, len, ALG_MAX_PAGES, 0, &off);
if (n < 0)
return n;

+ sgl->need_unpin = iov_iter_extract_will_pin(iter);
+
npages = DIV_ROUND_UP(off + n, PAGE_SIZE);
if (WARN_ON(npages == 0))
return -EINVAL;
@@ -573,8 +576,9 @@ void af_alg_free_sg(struct af_alg_sgl *sgl)
{
int i;

- for (i = 0; i < sgl->npages; i++)
- put_page(sgl->pages[i]);
+ if (sgl->need_unpin)
+ for (i = 0; i < sgl->npages; i++)
+ unpin_user_page(sgl->pages[i]);
}
EXPORT_SYMBOL_GPL(af_alg_free_sg);

diff --git a/include/crypto/if_alg.h b/include/crypto/if_alg.h
index 7e76623f9ec3..46494b33f5bc 100644
--- a/include/crypto/if_alg.h
+++ b/include/crypto/if_alg.h
@@ -59,6 +59,7 @@ struct af_alg_sgl {
struct scatterlist sg[ALG_MAX_PAGES + 1];
struct page *pages[ALG_MAX_PAGES];
unsigned int npages;
+ bool need_unpin;
};

/* TX SGL entry */