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qrexec: fix deadlock in qrexec-client

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When VM-VM qrexec service is called, two qrexec-clients are connected in
dom0. If both VMs are sending data simultaneously it can happen that
both qrexec-client processes will call write(2) and none of them will be
reading -> deadlock.
Solve it by handling I/O in two separate threads (one for reading from
VM, another for writing), at any time qrexec-client is ready to accept
data from either direction.
This commit is contained in:
Marek Marczykowski-Górecki 2014-07-01 03:24:46 +02:00
parent 6ab53c9456
commit 79abec9038
2 changed files with 18 additions and 22 deletions
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2
qrexec/Makefile
View File

@ -7,6 +7,6 @@ all: qrexec-daemon qrexec-client
qrexec-daemon: qrexec-daemon.o
$(CC) -pie -g -o qrexec-daemon qrexec-daemon.o $(LIBS)
qrexec-client: qrexec-client.o
$(CC) -pie -g -o qrexec-client qrexec-client.o $(LIBS)
$(CC) -pie -g -o qrexec-client qrexec-client.o $(LIBS) -lpthread
clean:
rm -f *.o *~ qrexec-daemon qrexec-client

38
qrexec/qrexec-client.c
View File

@ -27,6 +27,7 @@
#include <unistd.h>
#include <sys/wait.h>
#include <errno.h>
#include <pthread.h>
#include "qrexec.h"
#include "libqrexec-utils.h"
@ -225,30 +226,25 @@ void handle_daemon_only_until_writable(int s)
} while (!FD_ISSET(s, &wrset));
}
void *input_process_loop(void *arg) {
int s = *(int*)arg;
while (local_stdout_fd != -1)
handle_input(s);
return NULL;
}
void select_loop(int s)
{
fd_set select_set;
int max;
for (;;) {
handle_daemon_only_until_writable(s);
FD_ZERO(&select_set);
FD_SET(s, &select_set);
max = s;
if (local_stdout_fd != -1) {
FD_SET(local_stdout_fd, &select_set);
if (s < local_stdout_fd)
max = local_stdout_fd;
}
if (select(max + 1, &select_set, NULL, NULL, NULL) < 0) {
perror("select");
do_exit(1);
}
if (FD_ISSET(s, &select_set))
handle_daemon_data(s);
if (local_stdout_fd != -1
&& FD_ISSET(local_stdout_fd, &select_set))
handle_input(s);
pthread_t input_thread;
if (pthread_create(&input_thread, NULL, input_process_loop, &s) != 0) {
perror("pthread_create");
do_exit(1);
}
for (;;) {
handle_daemon_data(s);
}
pthread_join(input_thread, NULL);
}
void usage(const char *name)