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app.c: make sure that no non-async-signal-safe syscalls are used after

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fork before exec

Posix does only allow async-signal-safe syscalls after fork before exec.
As asterisk ignores this, functions like TrySystem or System sometimes
end up in a deadlocked child process. The patch prevents the use of
non-async-signal-safe syscalls.

ASTERISK-28776

Change-Id: Idc76365c0592ee3f3b3bd72a4f48f7a098978e8e
This commit is contained in:
Pirmin Walthert
2020-04-14 18:02:19 +02:00
committed by George Joseph
parent f56149d019
commit 6649b13b91
3 changed files with 75 additions and 58 deletions
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94
main/strcompat.c
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@@ -38,6 +38,8 @@
#include "asterisk/utils.h"
#define POLL_SIZE 1024
#ifndef HAVE_STRSEP
char *strsep(char **str, const char *delims)
{
@@ -426,59 +428,69 @@ int ffsll(long long n)
#ifndef HAVE_CLOSEFROM
void closefrom(int n)
{
long x;
int maxfd;
#ifndef _SC_OPEN_MAX
struct rlimit rl;
DIR *dir;
char path[16], *result;
struct dirent *entry;
#endif
struct pollfd fds[POLL_SIZE];
int fd=n, loopmax, i;
#ifndef STRICT_COMPAT
long flags;
#endif
snprintf(path, sizeof(path), "/proc/%d/fd", (int) getpid());
if ((dir = opendir(path))) {
while ((entry = readdir(dir))) {
/* Skip . and .. */
if (entry->d_name[0] == '.') {
#ifndef _SC_OPEN_MAX
if (getrlimit(RLIMIT_NOFILE, &rl) == -1) {
maxfd = -1;
} else {
maxfd = rl.rlim_cur;
}
#else
maxfd = sysconf (_SC_OPEN_MAX);
#endif
if (maxfd == -1 || maxfd > 65536) {
/* A more reasonable value. Consider that the primary source of
* file descriptors in Asterisk are UDP sockets, of which we are
* limited to 65,535 per address. We additionally limit that down
* to about 10,000 sockets per protocol. While the kernel will
* allow us to set the fileno limit higher (up to 4.2 billion),
* there really is no practical reason for it to be that high.
*
* sysconf as well as getrlimit can return -1 on error. Let's set
* maxfd to the mentioned reasonable value of 65,535 in this case.
*/
maxfd = 65536;
}
while (fd < maxfd) {
loopmax = maxfd - fd;
if (loopmax > POLL_SIZE) {
loopmax = POLL_SIZE;
}
for (i = 0; i < loopmax; i++) {
fds[i].fd = fd+i;
fds[i].events = 0;
}
poll(fds, loopmax, 0);
for (i = 0; i < loopmax; i++) {
if (fds[i].revents == POLLNVAL) {
continue;
}
if ((x = strtol(entry->d_name, &result, 10)) && x >= n) {
#ifdef STRICT_COMPAT
close(x);
close(fds[i].fd);
#else
/* This isn't strictly compatible, but it's actually faster
* for our purposes to set the CLOEXEC flag than to close
* file descriptors.
*/
long flags = fcntl(x, F_GETFD);
if (flags == -1 && errno == EBADF) {
continue;
}
fcntl(x, F_SETFD, flags | FD_CLOEXEC);
#endif
}
}
closedir(dir);
} else {
getrlimit(RLIMIT_NOFILE, &rl);
if (rl.rlim_cur > 65535) {
/* A more reasonable value. Consider that the primary source of
* file descriptors in Asterisk are UDP sockets, of which we are
* limited to 65,535 per address. We additionally limit that down
* to about 10,000 sockets per protocol. While the kernel will
* allow us to set the fileno limit higher (up to 4.2 billion),
* there really is no practical reason for it to be that high.
/* This isn't strictly compatible, but it's actually faster
* for our purposes to set the CLOEXEC flag than to close
* file descriptors.
*/
rl.rlim_cur = 65535;
}
for (x = n; x < rl.rlim_cur; x++) {
#ifdef STRICT_COMPAT
close(x);
#else
long flags = fcntl(x, F_GETFD);
flags = fcntl(fds[i].fd, F_GETFD);
if (flags == -1 && errno == EBADF) {
continue;
}
fcntl(x, F_SETFD, flags | FD_CLOEXEC);
fcntl(fds[i].fd, F_SETFD, flags | FD_CLOEXEC);
#endif
}
fd += loopmax;
}
}
#endif