gtp: allow -1 to be specified as file description from userspace

Existing user space applications maintained by the Osmocom project are
breaking since a recent fix that addresses incorrect error checking.

Restore operation for user space programs that specify -1 as file
descriptor to skip GTPv0 or GTPv1 only sockets.

Fixes: defd8b3c37b0 ("gtp: fix a potential NULL pointer dereference")
Reported-by: Pau Espin Pedrol <pespin@sysmocom.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Tested-by: Oliver Smith <osmith@sysmocom.de>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241022144825.66740-1-pablo@netfilter.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
index a60bfb1abb7f01e41cfe1986fa764bc8df0525de..70f981887518aaab77c568f4eb381f2bb36429b0 100644 (file)
--- a/drivers/net/gtp.c
+++ b/drivers/net/gtp.c
@@ -1702,20 +1702,24 @@ static int gtp_encap_enable(struct gtp_dev *gtp, struct nlattr *data[])
                return -EINVAL;
 
        if (data[IFLA_GTP_FD0]) {
-               u32 fd0 = nla_get_u32(data[IFLA_GTP_FD0]);
+               int fd0 = nla_get_u32(data[IFLA_GTP_FD0]);
 
-               sk0 = gtp_encap_enable_socket(fd0, UDP_ENCAP_GTP0, gtp);
-               if (IS_ERR(sk0))
-                       return PTR_ERR(sk0);
+               if (fd0 >= 0) {
+                       sk0 = gtp_encap_enable_socket(fd0, UDP_ENCAP_GTP0, gtp);
+                       if (IS_ERR(sk0))
+                               return PTR_ERR(sk0);
+               }
        }
 
        if (data[IFLA_GTP_FD1]) {
-               u32 fd1 = nla_get_u32(data[IFLA_GTP_FD1]);
+               int fd1 = nla_get_u32(data[IFLA_GTP_FD1]);
 
-               sk1u = gtp_encap_enable_socket(fd1, UDP_ENCAP_GTP1U, gtp);
-               if (IS_ERR(sk1u)) {
-                       gtp_encap_disable_sock(sk0);
-                       return PTR_ERR(sk1u);
+               if (fd1 >= 0) {
+                       sk1u = gtp_encap_enable_socket(fd1, UDP_ENCAP_GTP1U, gtp);
+                       if (IS_ERR(sk1u)) {
+                               gtp_encap_disable_sock(sk0);
+                               return PTR_ERR(sk1u);
+                       }
                }
        }