The patch fixes a bug introduced by commit c9c37e2e6378 ("fuse: switch to
iov_iter_get_pages()"):
The third argument of fuse_get_user_pages() "nbytesp" refers to the number of
bytes a caller asked to pack into fuse request. This value may be lesser
than capacity of fuse request or iov_iter. So fuse_get_user_pages() must
ensure that *nbytesp won't grow. Before that commit, it was ensured by:
> ret = get_user_pages_fast(user_addr, npages, !write,
> &req->pages[req->num_pages]);
> ...
> npages = ret;
> frag_size = min_t(size_t, frag_size,
> (npages << PAGE_SHIFT) - offset);
Now, when helper iov_iter_get_pages() performs all hard work of extracting
pages from iov_iter, it can be done by passing properly calculated "maxsize"
to the helper.
Reported-by: Werner Baumann <werner.baumann@xxxxxxxxxxxxx>
Signed-off-by: Maxim Patlasov <mpatlasov@xxxxxxxxxxxxx>
---
fs/fuse/file.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 40ac262..1d2bb70 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1303,10 +1303,15 @@ static int fuse_get_user_pages(struct fuse_req *req, struct iov_iter *ii,
while (nbytes < *nbytesp && req->num_pages < req->max_pages) {
unsigned npages;
size_t start;
+ ssize_t ret;
unsigned n = req->max_pages - req->num_pages;
- ssize_t ret = iov_iter_get_pages(ii,
- &req->pages[req->num_pages],
- n * PAGE_SIZE, &start);
+ size_t frag_size = fuse_get_frag_size(ii, *nbytesp - nbytes);
+
+ frag_size = min_t(size_t, frag_size, n << PAGE_SHIFT);
+
+ ret = iov_iter_get_pages(ii,
+ &req->pages[req->num_pages],
+ frag_size, &start);
if (ret < 0)
return ret;
--
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