mail: deobfuscate launch_helper()
13 bytes are not worth the risk of doing something iffy after vfork(). Let's have much clearer code there. function old new delta launch_helper 175 188 +13 Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
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@ -10,35 +10,35 @@
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#include "libbb.h"
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#include "mail.h"
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// generic signal handler
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// common signal handler
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static void signal_handler(int signo)
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{
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#define err signo
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if (SIGALRM == signo) {
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bb_simple_error_msg_and_die("timed out");
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}
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// SIGCHLD. reap zombies
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if (safe_waitpid(G.helper_pid, &err, WNOHANG) > 0) {
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if (WIFSIGNALED(err))
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bb_error_msg_and_die("helper killed by signal %u", WTERMSIG(err));
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if (WIFEXITED(err)) {
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G.helper_pid = 0;
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if (WEXITSTATUS(err))
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bb_error_msg_and_die("helper exited (%u)", WEXITSTATUS(err));
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}
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// SIGCHLD. reap the zombie if we expect one
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if (G.helper_pid == 0)
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return;
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#define status signo
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if (safe_waitpid(G.helper_pid, &status, WNOHANG) > 0) {
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G.helper_pid = 0;
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if (WIFSIGNALED(status))
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bb_error_msg_and_die("helper killed by signal %u", WTERMSIG(status));
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if (WIFEXITED(status) && WEXITSTATUS(status) != 0)
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bb_error_msg_and_die("helper exited (%u)", WEXITSTATUS(status));
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}
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#undef err
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#undef status
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}
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void FAST_FUNC launch_helper(const char **argv)
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{
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// setup vanilla unidirectional pipes interchange
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int i;
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int pipes[4];
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pid_t pid;
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struct fd_pair child_out;
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struct fd_pair child_in;
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xpipe(pipes);
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xpipe(pipes + 2);
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xpiped_pair(child_out);
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xpiped_pair(child_in);
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// NB: handler must be installed before vfork
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bb_signals(0
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@ -46,25 +46,23 @@ void FAST_FUNC launch_helper(const char **argv)
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+ (1 << SIGALRM)
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, signal_handler);
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G.helper_pid = xvfork();
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i = (!G.helper_pid) * 2; // for parent:0, for child:2
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close(pipes[i + 1]); // 1 or 3 - closing one write end
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close(pipes[2 - i]); // 2 or 0 - closing one read end
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xmove_fd(pipes[i], STDIN_FILENO); // 0 or 2 - using other read end
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xmove_fd(pipes[3 - i], STDOUT_FILENO); // 3 or 1 - using other write end
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// End result:
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// parent stdout [3] -> child stdin [2]
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// child stdout [1] -> parent stdin [0]
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if (!G.helper_pid) {
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G.helper_pid = pid = xvfork();
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if (pid == 0) {
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// child
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close(child_in.wr);
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close(child_out.rd);
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xmove_fd(child_in.rd, STDIN_FILENO);
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xmove_fd(child_out.wr, STDOUT_FILENO);
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// if parent dies, get SIGTERM
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prctl(PR_SET_PDEATHSIG, SIGTERM, 0, 0, 0);
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// try to execute connection helper
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// NB: SIGCHLD & SIGALRM revert to SIG_DFL on exec
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BB_EXECVP_or_die((char**)argv);
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}
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close(child_out.wr);
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close(child_in.rd);
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xmove_fd(child_out.rd, STDIN_FILENO);
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xmove_fd(child_in.wr, STDOUT_FILENO);
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// parent goes on
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}
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