crypto: digest: fix digesting file windows

When digesting a file we always try toread PAGE_SIZE bytes. When we get a
short read because we reached the file end then the code works
correctly. If instead we only want to digest a part of the file then
we must make sure to only read up to 'size' bytes.

Fixes: b77582effd ("crypto: digest: Split memory vs. file code into separate functions")

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 6 insertions, 5 deletions

diff --git a/crypto/digest.c b/crypto/digest.c
index 2c4de2e4f1..360c261e40 100644
--- a/crypto/digest.c
+++ b/crypto/digest.c
@@ -233,17 +233,18 @@ static int digest_update_from_fd(struct digest *d, int fd,
 	}
 
 	while (size) {
-		const ssize_t now = read(fd, buf, PAGE_SIZE);
-		if (now < 0) {
-			ret = now;
+		unsigned long now = min_t(typeof(size), PAGE_SIZE, size);
+
+		ret = read(fd, buf, now);
+		if (ret < 0) {
 			perror("read");
 			goto out_free;
 		}
 
-		if (!now)
+		if (!ret)
 			break;
 
-		ret = digest_update_interruptible(d, buf, now);
+		ret = digest_update_interruptible(d, buf, ret);
 		if (ret)
 			goto out_free;