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incidentd: fix race in waitpid_with_timeout

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waitpid_with_timeout has a race between a child process exiting and
the signal being blocked. Add an early waitpid to detect a child that
exited quickly.

Test: TH
Bug: 215574756
Change-Id: I6c7e9998d5b848c6144769f218fbcd7a0ee154bf
(cherry picked from commit 1f3012d223)
This commit is contained in:
Tim Murray
2022-02-17 12:36:33 -08:00
parent 7f9d05c6d2
commit 2538e20d62
1 changed files with 27 additions and 12 deletions
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39
cmds/incidentd/src/incidentd_util.cpp
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@ -184,11 +184,26 @@ static bool waitpid_with_timeout(pid_t pid, int timeout_ms, int* status) {
sigemptyset(&child_mask); sigemptyset(&child_mask);
sigaddset(&child_mask, SIGCHLD); sigaddset(&child_mask, SIGCHLD);
// block SIGCHLD before we check if a process has exited
if (sigprocmask(SIG_BLOCK, &child_mask, &old_mask) == -1) { if (sigprocmask(SIG_BLOCK, &child_mask, &old_mask) == -1) {
ALOGW("sigprocmask failed: %s", strerror(errno)); ALOGW("*** sigprocmask failed: %s\n", strerror(errno));
return false; return false;
} }
// if the child has exited already, handle and reset signals before leaving
pid_t child_pid = waitpid(pid, status, WNOHANG);
if (child_pid != pid) {
if (child_pid > 0) {
ALOGW("*** Waiting for pid %d, got pid %d instead\n", pid, child_pid);
sigprocmask(SIG_SETMASK, &old_mask, nullptr);
return false;
}
} else {
sigprocmask(SIG_SETMASK, &old_mask, nullptr);
return true;
}
// wait for a SIGCHLD
timespec ts; timespec ts;
ts.tv_sec = timeout_ms / 1000; ts.tv_sec = timeout_ms / 1000;
ts.tv_nsec = (timeout_ms % 1000) * 1000000; ts.tv_nsec = (timeout_ms % 1000) * 1000000;
@ -197,7 +212,7 @@ static bool waitpid_with_timeout(pid_t pid, int timeout_ms, int* status) {
// Set the signals back the way they were. // Set the signals back the way they were.
if (sigprocmask(SIG_SETMASK, &old_mask, nullptr) == -1) { if (sigprocmask(SIG_SETMASK, &old_mask, nullptr) == -1) {
ALOGW("sigprocmask failed: %s", strerror(errno)); ALOGW("*** sigprocmask failed: %s\n", strerror(errno));
if (ret == 0) { if (ret == 0) {
return false; return false;
} }
@ -207,21 +222,21 @@ static bool waitpid_with_timeout(pid_t pid, int timeout_ms, int* status) {
if (errno == EAGAIN) { if (errno == EAGAIN) {
errno = ETIMEDOUT; errno = ETIMEDOUT;
} else { } else {
ALOGW("sigtimedwait failed: %s", strerror(errno)); ALOGW("*** sigtimedwait failed: %s\n", strerror(errno));
} }
return false; return false;
} }
pid_t child_pid = waitpid(pid, status, WNOHANG); child_pid = waitpid(pid, status, WNOHANG);
if (child_pid == pid) { if (child_pid != pid) {
return true; if (child_pid != -1) {
ALOGW("*** Waiting for pid %d, got pid %d instead\n", pid, child_pid);
} else {
ALOGW("*** waitpid failed: %s\n", strerror(errno));
}
return false;
} }
if (child_pid == -1) { return true;
ALOGW("waitpid failed: %s", strerror(errno));
} else {
ALOGW("Waiting for pid %d, got pid %d instead", pid, child_pid);
}
return false;
} }
status_t kill_child(pid_t pid) { status_t kill_child(pid_t pid) {