fixeria has uploaded this change for review.
vty: clamp configured snaplen to the wire-framing limit
osmo-pcap carries each captured packet in a frame whose length field
(struct osmo_pcap_data.len) is a uint16_t, so any snaplen above ~64 KiB
cannot be transported and is silently clamped by the server when sizing
its receive buffer (calc_data_max_len() caps at UINT16_MAX). The VTY,
however, advertised libpcap's MAXIMUM_SNAPLEN (262144), misleading users
into configuring values that never take effect.
Introduce OSMO_PCAP_MAX_SNAPLEN (65535) and, in both the client "pcap
snaplen" and server "max-snaplen" handlers, warn and cap the value to it
when a larger one is given. The command syntax keeps the <1-262144>
range for backwards compatibility so existing configs still parse; the
help text now documents the effective 64 KiB limit.
Related: SYS#8099
Related: 6d2f7c52 ("server: Limit rx buffer size to UINT16_MAX")
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Change-Id: Ia56cad48e8cefe8ae103f2f7d2e037bf28438b71
---
M doc/manuals/chapters/client.adoc
M doc/manuals/chapters/server.adoc
M include/osmo-pcap/common.h
M src/osmo_client_vty.c
M src/osmo_server_vty.c
5 files changed, 43 insertions(+), 5 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/osmo-pcap refs/changes/36/42836/1
diff --git a/doc/manuals/chapters/client.adoc b/doc/manuals/chapters/client.adoc
index d9885d1..87682c5 100644
--- a/doc/manuals/chapters/client.adoc
+++ b/doc/manuals/chapters/client.adoc
@@ -67,6 +67,12 @@
the captured interface (e.g. `ethtool -K <iface> gro off lro off gso off tso
off`).
+NOTE:: Even though larger values are accepted for backwards compatibility, the
+osmo-pcap wire framing limits the effective snapshot length to 64 KiB
+(65535 bytes). Configuring a `snaplen` above 65535 is capped to 65535 with a
+warning on the VTY. The server's `max-snaplen` must be greater than or equal to
+the `snaplen` configured here.
+
Adding or removing new recording network devices during operation is not really
supported, and a restart of osmo-pcap-client is expected for the new
configuration to be properly set up.
diff --git a/doc/manuals/chapters/server.adoc b/doc/manuals/chapters/server.adoc
index 5d6ed32..f7a8290 100644
--- a/doc/manuals/chapters/server.adoc
+++ b/doc/manuals/chapters/server.adoc
@@ -39,7 +39,7 @@
base-path /var/lib/osmo-pcap-server <1>
server ip 192.168.11.20 <2>
server port 54321 <3>
- max-snaplen 100000 <4>
+ max-snaplen 65535 <4>
----
<1> directory to which the pcap files are stored
<2> IP address to which to bind/listen
@@ -52,6 +52,11 @@
larger `max-snaplen` on the server than the `snaplen` used by some clients; each
client's trace is recorded using that client's own snaplen.
+NOTE: Even though larger values are accepted for backwards compatibility, the
+osmo-pcap wire framing limits the effective snapshot length to 64 KiB
+(65535 bytes). Configuring a `max-snaplen` above 65535 is capped to 65535 with a
+warning on the VTY.
+
The received packets are stored to a pcap file below the `base-path` using a filename
encoding both the client name and the date/time at time of file creation.
diff --git a/include/osmo-pcap/common.h b/include/osmo-pcap/common.h
index 5916c48..b976a20 100644
--- a/include/osmo-pcap/common.h
+++ b/include/osmo-pcap/common.h
@@ -62,6 +62,13 @@
#define MAXIMUM_SNAPLEN 262144
#endif
+/* osmo-pcap transports each captured packet inside a frame whose length field
+ * (struct osmo_pcap_data.len) is a uint16_t. Hence the largest snaplen that can
+ * actually be carried over the wire is bounded by UINT16_MAX, far below
+ * libpcap's MAXIMUM_SNAPLEN (262144). The server enforces the same ceiling when
+ * sizing its per-connection receive buffer (see calc_data_max_len()). */
+#define OSMO_PCAP_MAX_SNAPLEN 65535
+
#define DEFAULT_SNAPLEN 9000
#endif
diff --git a/src/osmo_client_vty.c b/src/osmo_client_vty.c
index 127e52f..6bee983 100644
--- a/src/osmo_client_vty.c
+++ b/src/osmo_client_vty.c
@@ -198,9 +198,19 @@
DEFUN(cfg_client_snaplen,
cfg_client_snaplen_cmd,
"pcap snaplen <1-262144>", /* MAXIMUM_SNAPLEN */
- PCAP_STRING "snapshot length\n" "Bytes\n")
+ PCAP_STRING "snapshot length\n"
+ "Bytes (effectively limited to 64 KiB by the osmo-pcap wire framing)\n")
{
- pcap_client->snaplen = atoi(argv[0]);
+ int snaplen = atoi(argv[0]);
+
+ if (snaplen > OSMO_PCAP_MAX_SNAPLEN) {
+ vty_out(vty, "%% snaplen %d exceeds the limit imposed by the "
+ "osmo-pcap wire framing, capping to %d%s",
+ snaplen, OSMO_PCAP_MAX_SNAPLEN, VTY_NEWLINE);
+ snaplen = OSMO_PCAP_MAX_SNAPLEN;
+ }
+
+ pcap_client->snaplen = snaplen;
return CMD_SUCCESS;
}
diff --git a/src/osmo_server_vty.c b/src/osmo_server_vty.c
index dfe9857..fcf1db1 100644
--- a/src/osmo_server_vty.c
+++ b/src/osmo_server_vty.c
@@ -373,9 +373,19 @@
DEFUN(cfg_server_max_snaplen,
cfg_server_max_snaplen_cmd,
"max-snaplen <1-262144>", /* MAXIMUM_SNAPLEN */
- "Maximum pcap snapshot length\n" "Bytes\n")
+ "Maximum pcap snapshot length\n"
+ "Bytes (effectively limited to 64 KiB by the osmo-pcap wire framing)\n")
{
- pcap_server->max_snaplen = atoi(argv[0]);
+ int snaplen = atoi(argv[0]);
+
+ if (snaplen > OSMO_PCAP_MAX_SNAPLEN) {
+ vty_out(vty, "%% max-snaplen %d exceeds the limit imposed by the "
+ "osmo-pcap wire framing, capping to %d%s",
+ snaplen, OSMO_PCAP_MAX_SNAPLEN, VTY_NEWLINE);
+ snaplen = OSMO_PCAP_MAX_SNAPLEN;
+ }
+
+ pcap_server->max_snaplen = snaplen;
return CMD_SUCCESS;
}
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