netdev - [PATCH iproute2] libnetlink.c, ss.c: properly handle fread() error

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Date:   Thu, 24 Oct 2019 23:20:01 +0200
From:   Michał Łyszczek <michal.lyszczek@...c.pl>
To:     netdev@...r.kernel.org
Cc:     Michał Łyszczek <michal.lyszczek@...c.pl>
Subject: [PATCH iproute2] libnetlink.c, ss.c: properly handle fread() error

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 if return is 0 and then check error
indicator with ferror(3).

Signed-off-by: Michał Łyszczek <michal.lyszczek@...c.pl>
---
 lib/libnetlink.c | 6 +++---
 misc/ss.c        | 7 ++++---
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index 6ce8b199..76c383f9 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -1174,7 +1174,7 @@ int rtnl_listen(struct rtnl_handle *rtnl,
 int rtnl_from_file(FILE *rtnl, rtnl_listen_filter_t handler,
 		   void *jarg)
 {
-	int status;
+	size_t status;
 	char buf[16384];
 	struct nlmsghdr *h = (struct nlmsghdr *)buf;
 
@@ -1184,7 +1184,7 @@ int rtnl_from_file(FILE *rtnl, rtnl_listen_filter_t handler,
 
 		status = fread(&buf, 1, sizeof(*h), rtnl);
 
-		if (status < 0) {
+		if (status == 0 && ferror(rtnl)) {
 			if (errno == EINTR)
 				continue;
 			perror("rtnl_from_file: fread");
@@ -1204,7 +1204,7 @@ int rtnl_from_file(FILE *rtnl, rtnl_listen_filter_t handler,
 
 		status = fread(NLMSG_DATA(h), 1, NLMSG_ALIGN(l), rtnl);
 
-		if (status < 0) {
+		if (status == 0 && ferror(rtnl)) {
 			perror("rtnl_from_file: fread");
 			return -1;
 		}
diff --git a/misc/ss.c b/misc/ss.c
index 363b4c8d..769332e9 100644
--- a/misc/ss.c
+++ b/misc/ss.c
@@ -3329,12 +3329,13 @@ static int tcp_show_netlink_file(struct filter *f)
 	}
 
 	while (1) {
-		int status, err2;
+		int err2;
+		size_t status;
 		struct nlmsghdr *h = (struct nlmsghdr *)buf;
 		struct sockstat s = {};
 
 		status = fread(buf, 1, sizeof(*h), fp);
-		if (status < 0) {
+		if (status == 0 && ferror(fp)) {
 			perror("Reading header from $TCPDIAG_FILE");
 			break;
 		}
@@ -3345,7 +3346,7 @@ static int tcp_show_netlink_file(struct filter *f)
 
 		status = fread(h+1, 1, NLMSG_ALIGN(h->nlmsg_len-sizeof(*h)), fp);
 
-		if (status < 0) {
+		if (status == 0 && ferror(fp)) {
 			perror("Reading $TCPDIAG_FILE");
 			break;
 		}
-- 
2.21.0