[PATCH] tee: fix register_shm_helper()

[Jens Wiklander]

In register_shm_helper(), fix incorrect error handling for a call to
iov_iter_extract_pages(). A case is missing for when
iov_iter_extract_pages() only got some pages and return a number larger
than 0, but not the requested amount.

This fixes a possible NULL pointer dereference following a bad input from
ioctl(TEE_IOC_SHM_REGISTER) where parts of the buffer isn't mapped.

Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Masami Ichikawa <masami256@xxxxxxxxx>
Closes: https://lore.kernel.org/op-tee/CACOXgS-Bo2W72Nj1_44c7bntyNYOavnTjJAvUbEiQfq=u9W+-g@xxxxxxxxxxxxxx/
Fixes: 7bdee4157591 ("tee: Use iov_iter to better support shared buffer registration")
Signed-off-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
---
 drivers/tee/tee_shm.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
index daf6e5cfd59a..6ed7d030f4ed 100644
--- a/drivers/tee/tee_shm.c
+++ b/drivers/tee/tee_shm.c
@@ -316,7 +316,16 @@ register_shm_helper(struct tee_context *ctx, struct iov_iter *iter, u32 flags,
 
 	len = iov_iter_extract_pages(iter, &shm->pages, LONG_MAX, num_pages, 0,
 				     &off);
-	if (unlikely(len <= 0)) {
+	if (DIV_ROUND_UP(len + off, PAGE_SIZE) != num_pages) {
+		if (len > 0) {
+			/*
+			 * If we only got a few pages, update to release
+			 * the correct amount below.
+			 */
+			shm->num_pages = len / PAGE_SIZE;
+			ret = ERR_PTR(-ENOMEM);
+			goto err_put_shm_pages;
+		}
 		ret = len ? ERR_PTR(len) : ERR_PTR(-ENOMEM);
 		goto err_free_shm_pages;
 	}
-- 
2.43.0