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ssh_set_callbacks bug ?
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- Subject: ssh_set_callbacks bug ?
- From: Giovanni Panozzo <giovanni@xxxxxxxxxx>
- Reply-to: libssh@xxxxxxxxxx
- Date: Sun, 14 Feb 2016 11:21:10 +0100
- To: libssh@xxxxxxxxxx
Hi to all. I just subscribed to the list... but I think I have been subscribed in the past :)
While developing with libssh I have found the following problem: The lines at the end of ssh_set_callbacks() are: /* LEGACY */ if (ssh_get_log_callback() == NULL && cb->log_function) { ssh_set_log_callback(ssh_legacy_log_callback); ssh_set_log_userdata(session); } the last line store "session" (a short life variable) in a global variable.That pointer to "sesson" may become later no longer available during a program run. For example when you close/destroy your first session and then reopen a second and enable logging callback.
You can try to setup again callbacks to the second session, but if (ssh_get_log_callback() == NULL will prevent the call to ssh_set_log_userdata(). Crashing example here: -------------- #include <stdio.h> #include <malloc.h> #include <libssh/libssh.h> #include <libssh/callbacks.h> #include <stdlib.h>void mylogfunc(ssh_session session, int priority, const char *message, void *userdata)
{ printf("LOG MESSAGE: userdata=%p message=%s\n", userdata,message); } void onerun() { ssh_session sshs; struct ssh_callbacks_struct *cb; int rc; int verbosity = SSH_LOG_PROTOCOL; sshs = ssh_new(); if (sshs == NULL) { printf("ssh_new() failed\n"); return; } ssh_options_set(sshs, SSH_OPTIONS_HOST, "localhost"); ssh_options_set(sshs, SSH_OPTIONS_LOG_VERBOSITY, &verbosity); cb = malloc(sizeof(struct ssh_callbacks_struct)); memset(cb, 0, sizeof(struct ssh_callbacks_struct)); ssh_callbacks_init(cb); cb->log_function = mylogfunc; cb->userdata = NULL; ssh_set_callbacks(sshs, cb); rc = ssh_connect(sshs); if (rc != SSH_OK) { printf("Unable to connect to server\n"); } ssh_disconnect(sshs); ssh_free(sshs); free(cb); } int main() { onerun();// Allocate a new block of memory so ssh_new() will not reuse the old memory, // making the pointer saved in ssh_set_callbacks() with ssh_set_log_userdata()
// erroneously available again malloc(2000); onerun(); } -----As a workaround in user code, ssh_set_log_userdata(sshs) can be called just after a successful call to ssh_new.
-------------- Is this a bug or I'm doing something wrong ? Thank you Giovanni
Re: ssh_set_callbacks bug ? | Yanis Kurganov <yanis.kurganov@xxxxxxxxx> |
Re: ssh_set_callbacks bug ? | Andreas Schneider <asn@xxxxxxxxxxxxxx> |