[PATCH 3/3] smpp_smsc: Fix 32-bit signed integer overflow in read return value

[Daniel Willmann]

In case the length is 2^31+4 or larger we compute a negative value to
read in rdlen (since it is a signed int). This results in read failing
with EFAULT.

This patch changes the type of rdlen and rc to ssize_t (the return value
of read) and guards against the read length being larger than
(SSIZE_MAX).

To reproduce the issue run:
echo -e "\x80\x00\x00\x05\x00" |socat stdin tcp:localhost:2775
---
 openbsc/src/libmsc/smpp_smsc.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/openbsc/src/libmsc/smpp_smsc.c b/openbsc/src/libmsc/smpp_smsc.c
index a3dc311..23acfc2 100644
--- a/openbsc/src/libmsc/smpp_smsc.c
+++ b/openbsc/src/libmsc/smpp_smsc.c
@@ -23,6 +23,7 @@
 #include <string.h>
 #include <stdint.h>
 #include <errno.h>
+#include <limits.h>
 
 #include <sys/socket.h>
 #include <netinet/in.h>
@@ -770,8 +771,7 @@ static int esme_link_read_cb(struct osmo_fd *ofd)
        uint8_t *lenptr = (uint8_t *) &len;
        uint8_t *cur;
        struct msgb *msg;
-       int rdlen;
-       int rc;
+       ssize_t rdlen, rc;
 
        switch (esme->read_state) {
        case READ_ST_IN_LEN:
@@ -781,7 +781,7 @@ static int esme_link_read_cb(struct osmo_fd *ofd)
                        /* EINTR is a non-fatal error, just try again */
                        if (errno == EINTR)
                                return 0;
-                       LOGP(DSMPP, LOGL_ERROR, "[%s] read returned %d (%s)\n",
+                       LOGP(DSMPP, LOGL_ERROR, "[%s] read returned %zd (%s)\n",
                             esme->system_id, rc, strerror(errno));
                        goto dead_socket;
                } else if (rc == 0) {
@@ -790,8 +790,8 @@ static int esme_link_read_cb(struct osmo_fd *ofd)
                        esme->read_idx += rc;
                if (esme->read_idx >= sizeof(uint32_t)) {
                        esme->read_len = ntohl(len);
-                       if (esme->read_len <= 4) {
-                               LOGP(DSMPP, LOGL_ERROR, "[%s] read length too 
small %d\n",
+                       if (esme->read_len <= 4 || esme->read_len > SSIZE_MAX) {
+                               LOGP(DSMPP, LOGL_ERROR, "[%s] length invalid 
%d\n",
                                                esme->system_id, 
esme->read_len);
                                goto dead_socket;
                        }
@@ -811,7 +811,7 @@ static int esme_link_read_cb(struct osmo_fd *ofd)
                rdlen = esme->read_len - esme->read_idx;
                rc = read(ofd->fd, msg->tail, OSMO_MIN(rdlen, 
msgb_tailroom(msg)));
                if (rc < 0) {
-                       LOGP(DSMPP, LOGL_ERROR, "[%s] read returned %d (%s)\n",
+                       LOGP(DSMPP, LOGL_ERROR, "[%s] read returned %zd (%s)\n",
                                esme->system_id, rc, strerror(errno));
                        goto dead_socket;
                } else if (rc == 0) {
-- 
1.8.4.2