[PATCH net] Fix a potential infinite loop in extract_user_to_sg()

[David Howells]

Fix extract_user_to_sg() so that it will break out of the loop if
iov_iter_extract_pages() returns 0 rather than looping around forever.

[Note that I've included two fixes lines as the function got moved to a
different file and renamed]

Fixes: 85dd2c8ff368 ("netfs: Add a function to extract a UBUF or IOVEC into a BVEC iterator")
Fixes: f5f82cd18732 ("Move netfs_extract_iter_to_sg() to lib/scatterlist.c")
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Jeff Layton <jlayton@xxxxxxxxxx>
cc: Steve French <sfrench@xxxxxxxxx>
cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
cc: Eric Dumazet <edumazet@xxxxxxxxxx>
cc: Jakub Kicinski <kuba@xxxxxxxxxx>
cc: Paolo Abeni <pabeni@xxxxxxxxxx>
cc: netfs@xxxxxxxxxxxxxxx
cc: linux-crypto@xxxxxxxxxxxxxxx
cc: linux-cifs@xxxxxxxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
cc: netdev@xxxxxxxxxxxxxxx
---
 lib/scatterlist.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 68b45c82c37a..7bc2220fea80 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -1124,7 +1124,7 @@ static ssize_t extract_user_to_sg(struct iov_iter *iter,
 	do {
 		res = iov_iter_extract_pages(iter, &pages, maxsize, sg_max,
 					     extraction_flags, &off);
-		if (res < 0)
+		if (res <= 0)
 			goto failed;
 
 		len = res;