From 524ce20b55a2793d380fc1e4b415b1ea5a9512b1 Mon Sep 17 00:00:00 2001 From: Jeremy Sowden Date: Thu, 16 Mar 2023 11:07:54 +0000 Subject: pcap: prevent crashes when output `FILE *` is null If ulogd2 receives a signal it will attempt to re-open the pcap output file. If this fails (because the permissions or ownership have changed for example), the FILE pointer will be null and when the next packet comes in, the null pointer will be passed to fwrite and ulogd will crash. Instead, assign the return value of `fopen` to a local variable, and only close the existing stream if `fopen` succeeded. Link: https://bugs.launchpad.net/ubuntu/+source/ulogd2/+bug/1429778 Signed-off-by: Jeremy Sowden Signed-off-by: Florian Westphal --- output/pcap/ulogd_output_PCAP.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/output/pcap/ulogd_output_PCAP.c b/output/pcap/ulogd_output_PCAP.c index 0daa2c9..19ce47f 100644 --- a/output/pcap/ulogd_output_PCAP.c +++ b/output/pcap/ulogd_output_PCAP.c @@ -221,14 +221,20 @@ static int append_create_outfile(struct ulogd_pluginstance *upi) struct pcap_instance *pi = (struct pcap_instance *) &upi->private; char *filename = upi->config_kset->ces[0].u.string; struct stat st_of; + FILE *of; - pi->of = fopen(filename, "a"); - if (!pi->of) { + of = fopen(filename, "a"); + if (!of) { ulogd_log(ULOGD_ERROR, "can't open pcap file %s: %s\n", filename, strerror(errno)); return -EPERM; } + + if (pi->of) + fclose(pi->of); + pi->of = of; + if (fstat(fileno(pi->of), &st_of) == 0 && st_of.st_size == 0 && !write_pcap_header(pi)) { ulogd_log(ULOGD_ERROR, "can't write pcap header: %s\n", @@ -241,12 +247,9 @@ static int append_create_outfile(struct ulogd_pluginstance *upi) static void signal_pcap(struct ulogd_pluginstance *upi, int signal) { - struct pcap_instance *pi = (struct pcap_instance *) &upi->private; - switch (signal) { case SIGHUP: ulogd_log(ULOGD_NOTICE, "reopening capture file\n"); - fclose(pi->of); append_create_outfile(upi); break; default: -- cgit v1.2.3