conntrack: fix ftp ipv4 address substitution.

When replacing the ipv4 address in repl_ftp_v4_addr(), the remaining size
was incorrectly calculated which could lead to the wrong replacement
adjustment.

This goes unnoticed most of the time, unless you choose carefully your
initial and replacement addresses.

Example fail address combination with 10.1.1.200 DNAT'd to 10.1.100.1.

Fix this by doing something similar to V6 and also splicing out common
code for better coverage and maintainability.

A test is updated to exercise different initial and replacement addresses
and another test is added.

Fixes: bd5e81a0e596 ("Userspace Datapath: Add ALG infra and FTP.")
Reported-by: David Marchand <david.marchand@redhat.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Darrell Ball <dlu998@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

1 files changed, 56 insertions, 62 deletions

diff --git a/lib/conntrack.c b/lib/conntrack.c
index f732b9ee4..6b6675005 100644
--- a/lib/conntrack.c
+++ b/lib/conntrack.c
@@ -136,7 +136,7 @@ expectation_lookup(struct hmap *alg_expectations, const struct conn_key *key,
 static int
 repl_ftp_v4_addr(struct dp_packet *pkt, ovs_be32 v4_addr_rep,
                  char *ftp_data_v4_start,
-                 size_t addr_offset_from_ftp_data_start);
+                 size_t addr_offset_from_ftp_data_start, size_t addr_size);
 
 static enum ftp_ctl_pkt
 process_ftp_ctl_v4(struct conntrack *ct,
@@ -144,7 +144,8 @@ process_ftp_ctl_v4(struct conntrack *ct,
                    const struct conn *conn_for_expectation,
                    ovs_be32 *v4_addr_rep,
                    char **ftp_data_v4_start,
-                   size_t *addr_offset_from_ftp_data_start);
+                   size_t *addr_offset_from_ftp_data_start,
+                   size_t *addr_size);
 
 static enum ftp_ctl_pkt
 detect_ftp_ctl_type(const struct conn_lookup_ctx *ctx,
@@ -2771,13 +2772,6 @@ expectation_create(struct conntrack *ct, ovs_be16 dst_port,
     ct_rwlock_unlock(&ct->resources_lock);
 }
 
-static uint8_t
-get_v4_byte_be(ovs_be32 v4_addr, uint8_t index)
-{
-    uint8_t *byte_ptr = (OVS_FORCE uint8_t *) &v4_addr;
-    return byte_ptr[index];
-}
-
 static void
 replace_substring(char *substr, uint8_t substr_size,
                   uint8_t total_size, char *rep_str,
@@ -2788,51 +2782,56 @@ replace_substring(char *substr, uint8_t substr_size,
     memcpy(substr, rep_str, rep_str_size);
 }
 
+static void
+repl_bytes(char *str, char c1, char c2)
+{
+    while (*str) {
+        if (*str == c1) {
+            *str = c2;
+        }
+        str++;
+    }
+}
+
+static void
+modify_packet(struct dp_packet *pkt, char *pkt_str, size_t size,
+              char *repl_str, size_t repl_size,
+              uint32_t orig_used_size)
+{
+    replace_substring(pkt_str, size,
+                      (const char *) dp_packet_tail(pkt) - pkt_str,
+                      repl_str, repl_size);
+    dp_packet_set_size(pkt, orig_used_size + (int) repl_size - (int) size);
+}
+
 /* Replace IPV4 address in FTP message with NATed address. */
 static int
 repl_ftp_v4_addr(struct dp_packet *pkt, ovs_be32 v4_addr_rep,
                  char *ftp_data_start,
-                 size_t addr_offset_from_ftp_data_start)
+                 size_t addr_offset_from_ftp_data_start,
+                 size_t addr_size OVS_UNUSED)
 {
     enum { MAX_FTP_V4_NAT_DELTA = 8 };
 
     /* Do conservative check for pathological MTU usage. */
     uint32_t orig_used_size = dp_packet_size(pkt);
-    uint16_t allocated_size = dp_packet_get_allocated(pkt);
-    if (orig_used_size + MAX_FTP_V4_NAT_DELTA > allocated_size) {
+    if (orig_used_size + MAX_FTP_V4_NAT_DELTA >
+        dp_packet_get_allocated(pkt)) {
+
         static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(5, 5);
-        VLOG_WARN_RL(&rl, "Unsupported effective MTU %u used with FTP",
-                     allocated_size);
+        VLOG_WARN_RL(&rl, "Unsupported effective MTU %u used with FTP V4",
+                     dp_packet_get_allocated(pkt));
         return 0;
     }
 
-    size_t remain_size = tcp_payload_length(pkt) -
-                             addr_offset_from_ftp_data_start;
-    int overall_delta = 0;
-    char *byte_str = ftp_data_start + addr_offset_from_ftp_data_start;
-
-    /* Replace the existing IPv4 address by the new one. */
-    for (uint8_t i = 0; i < 4; i++) {
-        /* Find the end of the string for this octet. */
-        char *next_delim = memchr(byte_str, ',', 4);
-        ovs_assert(next_delim);
-        int substr_size = next_delim - byte_str;
-        remain_size -= substr_size;
-
-        /* Compose the new string for this octet, and replace it. */
-        char rep_str[4];
-        uint8_t rep_byte = get_v4_byte_be(v4_addr_rep, i);
-        int replace_size = sprintf(rep_str, "%d", rep_byte);
-        replace_substring(byte_str, substr_size, remain_size,
-                          rep_str, replace_size);
-        overall_delta += replace_size - substr_size;
-
-        /* Advance past the octet and the following comma. */
-        byte_str += replace_size + 1;
-    }
-
-    dp_packet_set_size(pkt, orig_used_size + overall_delta);
-    return overall_delta;
+    char v4_addr_str[INET_ADDRSTRLEN] = {0};
+    ovs_assert(inet_ntop(AF_INET, &v4_addr_rep, v4_addr_str,
+                         sizeof v4_addr_str));
+    repl_bytes(v4_addr_str, '.', ',');
+    modify_packet(pkt, ftp_data_start + addr_offset_from_ftp_data_start,
+                  addr_size, v4_addr_str, strlen(v4_addr_str),
+                  orig_used_size);
+    return (int) strlen(v4_addr_str) - (int) addr_size;
 }
 
 static char *
@@ -2901,7 +2900,8 @@ process_ftp_ctl_v4(struct conntrack *ct,
                    const struct conn *conn_for_expectation,
                    ovs_be32 *v4_addr_rep,
                    char **ftp_data_v4_start,
-                   size_t *addr_offset_from_ftp_data_start)
+                   size_t *addr_offset_from_ftp_data_start,
+                   size_t *addr_size)
 {
     struct tcp_header *th = dp_packet_l4(pkt);
     size_t tcp_hdr_len = TCP_OFFSET(th->tcp_ctl) * 4;
@@ -2957,6 +2957,7 @@ process_ftp_ctl_v4(struct conntrack *ct,
         return CT_FTP_CTL_INVALID;
     }
 
+    *addr_size = ftp - ip_addr_start - 1;
     char *save_ftp = ftp;
     ftp = terminate_number_str(ftp, MAX_FTP_PORT_DGTS);
     if (!ftp) {
@@ -3149,31 +3150,22 @@ repl_ftp_v6_addr(struct dp_packet *pkt, struct ct_addr v6_addr_rep,
 
     /* Do conservative check for pathological MTU usage. */
     uint32_t orig_used_size = dp_packet_size(pkt);
-    uint16_t allocated_size = dp_packet_get_allocated(pkt);
-    if (orig_used_size + MAX_FTP_V6_NAT_DELTA > allocated_size) {
+    if (orig_used_size + MAX_FTP_V6_NAT_DELTA >
+        dp_packet_get_allocated(pkt)) {
+
         static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(5, 5);
-        VLOG_WARN_RL(&rl, "Unsupported effective MTU %u used with FTP",
-                     allocated_size);
+        VLOG_WARN_RL(&rl, "Unsupported effective MTU %u used with FTP V6",
+                     dp_packet_get_allocated(pkt));
         return 0;
     }
 
     char v6_addr_str[IPV6_SCAN_LEN] = {0};
     ovs_assert(inet_ntop(AF_INET6, &v6_addr_rep.ipv6_aligned, v6_addr_str,
                          IPV6_SCAN_LEN - 1));
-
-    size_t replace_addr_size = strlen(v6_addr_str);
-
-    size_t remain_size = tcp_payload_length(pkt) -
-                             addr_offset_from_ftp_data_start;
-
-    char *pkt_addr_str = ftp_data_start + addr_offset_from_ftp_data_start;
-    replace_substring(pkt_addr_str, addr_size, remain_size,
-                      v6_addr_str, replace_addr_size);
-
-    int overall_delta = (int) replace_addr_size - (int) addr_size;
-
-    dp_packet_set_size(pkt, orig_used_size + overall_delta);
-    return overall_delta;
+    modify_packet(pkt, ftp_data_start + addr_offset_from_ftp_data_start,
+                  addr_size, v6_addr_str, strlen(v6_addr_str),
+                  orig_used_size);
+    return (int) strlen(v6_addr_str) - (int) addr_size;
 }
 
 /* Increment/decrement a TCP sequence number. */
@@ -3213,7 +3205,8 @@ handle_ftp_ctl(struct conntrack *ct, const struct conn_lookup_ctx *ctx,
         } else {
             rc = process_ftp_ctl_v4(ct, pkt, ec,
                                     &v4_addr_rep, &ftp_data_start,
-                                    &addr_offset_from_ftp_data_start);
+                                    &addr_offset_from_ftp_data_start,
+                                    &addr_size);
         }
         if (rc == CT_FTP_CTL_INVALID) {
             static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(5, 5);
@@ -3240,7 +3233,8 @@ handle_ftp_ctl(struct conntrack *ct, const struct conn_lookup_ctx *ctx,
                 if (nat) {
                     seq_skew = repl_ftp_v4_addr(pkt, v4_addr_rep,
                                    ftp_data_start,
-                                   addr_offset_from_ftp_data_start);
+                                   addr_offset_from_ftp_data_start,
+                                   addr_size);
                 }
                 if (seq_skew) {
                     ip_len = ntohs(l3_hdr->ip_tot_len) + seq_skew;