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global/global_init: fix stdout/stderr/stdin closing for daemonization

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The global_init_postfork/prefork helpers close stdout/stdin/stderr on
fork and reopen /dev/null in their place.  This ensures that if later
code writes to those descriptors (e.g., a stray cout or cerr usage) the
output/input will go nowhere instead of interfering with some other open
fd.

However, with the use of preforker, there are other threads running when
these helpers are run, which means we can race with, say, filestore
opening an object file and end up sending log output there.

Fix by atomically replacing the fds with the dup2(2) syscall, which
will implicitly close and reopen the target fd in an atomic fashion.  This
behavior is present on both Linux and FreeBSD.

Fixes: http://tracker.ceph.com/issues/23492
Signed-off-by: Sage Weil <sage@redhat.com>
This commit is contained in:
Sage Weil 2018-07-09 13:26:39 -05:00
parent 975528f632
commit 3c2d91ed11
1 changed files with 26 additions and 21 deletions
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47
src/global/global_init.cc
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@ -425,6 +425,29 @@ void global_init_daemonize(CephContext *cct)
#endif
}
int reopen_as_null(CephContext *cct, int fd)
{
int newfd = open("/dev/null", O_RDONLY);
if (newfd < 0) {
int err = errno;
lderr(cct) << __func__ << " failed to open /dev/null: " << cpp_strerror(err)
<< dendl;
return -1;
}
// atomically dup newfd to target fd. target fd is implicitly closed if
// open and atomically replaced; see man dup2
int r = dup2(newfd, fd);
if (r < 0) {
int err = errno;
lderr(cct) << __func__ << " failed to dup2 " << fd << ": "
<< cpp_strerror(err) << dendl;
return -1;
}
// close newfd (we cloned it to target fd)
VOID_TEMP_FAILURE_RETRY(close(newfd));
return 0;
}
void global_init_postfork_start(CephContext *cct)
{
// restart log thread
@ -439,13 +462,7 @@ void global_init_postfork_start(CephContext *cct)
* guarantee that nobody ever writes to stdout, even though they're not
* supposed to.
*/
VOID_TEMP_FAILURE_RETRY(close(STDIN_FILENO));
if (open("/dev/null", O_RDONLY) < 0) {
int err = errno;
derr << "global_init_daemonize: open(/dev/null) failed: error "
<< err << dendl;
exit(1);
}
reopen_as_null(cct, STDIN_FILENO);
const md_config_t *conf = cct->_conf;
if (pidfile_write(conf) < 0)
@ -473,13 +490,7 @@ void global_init_postfork_finish(CephContext *cct)
}
}
VOID_TEMP_FAILURE_RETRY(close(STDOUT_FILENO));
if (open("/dev/null", O_RDONLY) < 0) {
int err = errno;
derr << "global_init_daemonize: open(/dev/null) failed: error "
<< err << dendl;
exit(1);
}
reopen_as_null(cct, STDOUT_FILENO);
ldout(cct, 1) << "finished global_init_daemonize" << dendl;
}
@ -503,13 +514,7 @@ void global_init_chdir(const CephContext *cct)
*/
int global_init_shutdown_stderr(CephContext *cct)
{
VOID_TEMP_FAILURE_RETRY(close(STDERR_FILENO));
if (open("/dev/null", O_RDONLY) < 0) {
int err = errno;
derr << "global_init_shutdown_stderr: open(/dev/null) failed: error "
<< err << dendl;
return 1;
}
reopen_as_null(cct, STDERR_FILENO);
cct->_log->set_stderr_level(-1, -1);
return 0;
}