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iucvterm/iucvtty: Prevent connection stalls when receiving TERM env

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iucvtty expects to receive the TERM environment information right
after a connection has been established. Reading this information
can lead to a connection stall (DoS).  Introduce a temporary timeout
and fall back to the default TERM environment.

Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
This commit is contained in:
Hendrik Brueckner
2026-07-06 14:36:19 +02:00
committed by Jan Höppner
parent 29db9032b3
commit f67fa03581
1 changed files with 32 additions and 8 deletions
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40
iucvterm/src/iucvtty.c
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@@ -17,6 +17,7 @@
#include <string.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <syslog.h>
@@ -62,6 +63,36 @@ static int exec_login_prog(char *cmd[])
return rc;
}
/**
* receive_term_env() - receive terminal environment with timeout
* @term: Terminal environment variable
* @len: Maximum characters for the terminal environment variable
*/
static void receive_term_env(int client, char *term, size_t len)
{
struct timeval tv = { .tv_sec = 0, .tv_usec = 0};
/* Set a temporary timeout of 10s to time out a stalling
* client connection. Use SO_RCVTIMEO to set the timeout.
* Using those hard coded values directly is safe as
* SO_RCVTIMEO is not being used in other parts of iucvtty.
*/
tv.tv_sec = 10;
setsockopt(client, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
memset(term, 0, len);
if (iucvtty_rx_termenv(client, term, len))
snprintf(term, len, "%s", TERM_DEFAULT);
tv.tv_sec = 0;
setsockopt(client, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
if (!is_term_valid(term, len)) {
print_error("Ignoring received TERM env due to invalid character(s)");
snprintf(term, len, "%s", TERM_DEFAULT);
}
}
/**
* iucvtty_worker() - Handle an incoming client connection
* @client: Client file descriptor
@@ -88,14 +119,7 @@ static int iucvtty_worker(int client, int master, int slave,
tcflush(master, TCIOFLUSH);
/* read and validate terminal parameters from client */
memset(term_env, 0, sizeof(term_env));
if (iucvtty_rx_termenv(client, term_env, MAX_TERM_SIZE))
snprintf(term_env, sizeof(term_env), "%s", TERM_DEFAULT);
if (!is_term_valid(term_env, sizeof(term_env))) {
print_error("Ignoring received TERM env due to invalid character(s)");
snprintf(term_env, sizeof(term_env), "%s", TERM_DEFAULT);
}
receive_term_env(client, term_env, sizeof(term_env));
/* start login program */
child = fork();