libnetlink.c, ss.c: properly handle fread() errors

fread(3) returns size_t data type which is unsigned, thus check
`if (fread(...) < 0)' is always false. To check if fread(3) has
failed, user should check error indicator with ferror(3).

This commit also changes read logic a little bit by being less
forgiving for errors. Previous logic was checking if fread(3)
read *at least* required ammount of data, now code checks if
fread(3) read *exactly* expected ammount of data. This makes
sense because code parses very specific binary file, and reading
even 1 less/more byte than expected, will later corrupt data anyway.

Signed-off-by: Michał Łyszczek <michal.lyszczek@bofc.pl>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

1 files changed, 13 insertions, 13 deletions

diff --git a/misc/ss.c b/misc/ss.c
index 363b4c8d..efa87781 100644
--- a/misc/ss.c
+++ b/misc/ss.c
@@ -3329,28 +3329,28 @@ static int tcp_show_netlink_file(struct filter *f)
 	}
 
 	while (1) {
-		int status, err2;
+		int err2;
+		size_t status, nitems;
 		struct nlmsghdr *h = (struct nlmsghdr *)buf;
 		struct sockstat s = {};
 
 		status = fread(buf, 1, sizeof(*h), fp);
-		if (status < 0) {
-			perror("Reading header from $TCPDIAG_FILE");
-			break;
-		}
 		if (status != sizeof(*h)) {
-			perror("Unexpected EOF reading $TCPDIAG_FILE");
+			if (ferror(fp))
+				perror("Reading header from $TCPDIAG_FILE");
+			if (feof(fp))
+				fprintf(stderr, "Unexpected EOF reading $TCPDIAG_FILE");
 			break;
 		}
 
-		status = fread(h+1, 1, NLMSG_ALIGN(h->nlmsg_len-sizeof(*h)), fp);
+		nitems = NLMSG_ALIGN(h->nlmsg_len - sizeof(*h));
+		status = fread(h+1, 1, nitems, fp);
 
-		if (status < 0) {
-			perror("Reading $TCPDIAG_FILE");
-			break;
-		}
-		if (status + sizeof(*h) < h->nlmsg_len) {
-			perror("Unexpected EOF reading $TCPDIAG_FILE");
+		if (status != nitems) {
+			if (ferror(fp))
+				perror("Reading $TCPDIAG_FILE");
+			if (feof(fp))
+				fprintf(stderr, "Unexpected EOF reading $TCPDIAG_FILE");
 			break;
 		}