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dns: Fix bug in error handling when talking to script

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Comparing the result of read/write to a size_t value
is dangerous C. Since ssize_t and size_t have the same
size ssize_t is promoted to size_t, so -1 becomes
size_t max value and is not smaller than the expected
length.

Make sure to compare ssize_t to ssize_t to avoid any
suprises.

Change-Id: Ic395b6d1dce510bb4b499c5beba61f033a2a860b
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Heiko Hund <heiko@openvpn.net>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1208
Message-Id: <20250924121901.13532-1-gert@greenie.muc.de>
URL: https://sourceforge.net/p/openvpn/mailman/message/59238099/
Signed-off-by: Gert Doering <gert@greenie.muc.de>
This commit is contained in:
Frank Lichtenheld 2025-09-24 14:18:55 +02:00 committed by Gert Doering
parent 945db23ef4
commit bd27319f2a
1 changed files with 5 additions and 6 deletions
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11
src/openvpn/dns.c
View file

@ -642,11 +642,10 @@ run_updown_runner(bool up, struct options *o, const struct tuntap *tt,
while (1)
{
ssize_t rlen, wlen;
char path[PATH_MAX];
/* Block here until parent sends a path */
rlen = read(dns_pipe_fd[0], &path, sizeof(path));
ssize_t rlen = read(dns_pipe_fd[0], &path, sizeof(path));
if (rlen < 1)
{
if (rlen == -1 && errno == EINTR)
@ -665,8 +664,8 @@ run_updown_runner(bool up, struct options *o, const struct tuntap *tt,
/* Unblock parent process */
while (1)
{
wlen = write(ack_pipe_fd[1], &res, sizeof(res));
if ((wlen == -1 && errno != EINTR) || wlen < sizeof(res))
ssize_t wlen = write(ack_pipe_fd[1], &res, sizeof(res));
if ((wlen == -1 && errno != EINTR) || wlen < (ssize_t)sizeof(res))
{
/* Not much we can do about errors but exit */
close(dns_pipe_fd[0]);
@ -727,7 +726,7 @@ run_up_down_command(bool up, struct options *o, const struct tuntap *tt,
env_set_write_file(dvf, es);
int wfd = updown_runner->fds[1];
size_t dvf_size = strlen(dvf) + 1;
ssize_t dvf_size = strlen(dvf) + 1;
while (1)
{
ssize_t len = write(wfd, dvf, dvf_size);
@ -746,7 +745,7 @@ run_up_down_command(bool up, struct options *o, const struct tuntap *tt,
while (1)
{
ssize_t len = read(rfd, &status, sizeof(status));
if (len < sizeof(status))
if (len < (ssize_t)sizeof(status))
{
if (len == -1 && errno == EINTR)
{