Fix the case where we try to detach unattached processes
Before this change: $ strace -D -p1 strace: -D and -p are mutually exclusive options Process 1 detached <==== WRONG! (and we try to SIGSTOP it!!!) * defs.h: Change the meaning of TCB_ATTACHED: now it means "this tracee is attached to us". Add TCB_STRACE_CHILD: "this tracee is our child". * strace.c (kill_save_errno): Move up. No code changes. (process_opt_p_list): Don't set TCB_ATTACHED on new tcb. (startup_attach): Change how we work with TCB_ATTACHED. Set TCB_STRACE_CHILD on -D. (startup_child): Use kill_save_errno instead of kill. Set TCB_ATTACHED and TCB_STRACE_CHILD on attached strace child. If we are in -D case, don't set TCB_ATTACHED (we aren't attached yet). (detach): do not do PTRACE_DETACH if TCB_ATTACHED is not set. (cleanup): Check TCB_STRACE_CHILD instead of TCB_ATTACHED. (trace): Likewise. Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
parent
97c503fa2e
commit
75fe85c2ee
11
defs.h
11
defs.h
@ -352,14 +352,9 @@ struct tcb {
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* Use entering(tcp) / exiting(tcp) to check this bit to make code more readable.
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*/
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#define TCB_INSYSCALL 00010
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/*
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* Process is not our own child.
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* In "strace [-f] PROG" case, traced child (PROG) will have this bit not set,
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* but any its children (including threads) will.
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* Note: if bit is set, it does *not* mean that attaching was already done.
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* There is a small window at the init time when it's not true.
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*/
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#define TCB_ATTACHED 00020
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#define TCB_ATTACHED 00020 /* It is attached already */
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/* Are we PROG from "strace PROG [ARGS]" invocation? */
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#define TCB_STRACE_CHILD 00040
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#define TCB_BPTSET 00100 /* "Breakpoint" set after fork(2) */
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#define TCB_REPRINT 01000 /* We should reprint this syscall on exit */
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#define TCB_FILTERED 02000 /* This system call has been filtered out */
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115
strace.c
115
strace.c
@ -329,6 +329,14 @@ set_cloexec_flag(int fd)
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fcntl(fd, F_SETFD, newflags); /* never fails */
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}
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static void kill_save_errno(pid_t pid, int sig)
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{
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int saved_errno = errno;
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(void) kill(pid, sig);
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errno = saved_errno;
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}
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/*
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* When strace is setuid executable, we have to swap uids
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* before and after filesystem and process management operations.
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@ -429,7 +437,6 @@ static void process_opt_p_list(char *opt)
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* pidof uses space as delim, pgrep uses newline. :(
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*/
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int pid;
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struct tcb *tcp;
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char *delim = opt + strcspn(opt, ", \n\t");
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char c = *delim;
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@ -446,8 +453,7 @@ static void process_opt_p_list(char *opt)
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return;
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}
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*delim = c;
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tcp = alloc_tcb(pid, 0);
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tcp->flags |= TCB_ATTACHED;
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alloc_tcb(pid, 0);
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if (c == '\0')
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break;
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opt = delim + 1;
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@ -492,9 +498,12 @@ startup_attach(void)
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for (tcbi = 0; tcbi < tcbtabsize; tcbi++) {
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tcp = tcbtab[tcbi];
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if (!(tcp->flags & TCB_INUSE))
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continue;
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/* Is this a process we should attach to, but not yet attached? */
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if ((tcp->flags & (TCB_ATTACHED | TCB_STARTUP)) != TCB_ATTACHED)
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continue; /* no */
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if (tcp->flags & TCB_ATTACHED)
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continue; /* no, we already attached it */
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/* Reinitialize the output since it may have changed */
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tcp->outf = outf;
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@ -552,7 +561,7 @@ startup_attach(void)
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: "Process %u attached - interrupt to quit\n",
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tcp->pid, ntid);
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}
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if (!(tcp->flags & TCB_STARTUP)) {
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if (!(tcp->flags & TCB_ATTACHED)) {
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/* -p PID, we failed to attach to PID itself
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* but did attach to some of its sibling threads.
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* Drop PID's tcp.
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@ -567,7 +576,7 @@ startup_attach(void)
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droptcb(tcp);
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continue;
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}
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tcp->flags |= TCB_STARTUP | post_attach_sigstop;
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tcp->flags |= TCB_ATTACHED | TCB_STARTUP | post_attach_sigstop;
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if (debug)
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fprintf(stderr, "attach to pid %d (main) succeeded\n", tcp->pid);
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@ -576,7 +585,7 @@ startup_attach(void)
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* It is our grandparent we trace, not a -p PID.
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* Don't want to just detach on exit, so...
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*/
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tcp->flags &= ~TCB_ATTACHED;
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tcp->flags |= TCB_STRACE_CHILD;
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/*
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* Make parent go away.
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* Also makes grandparent's wait() unblock.
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@ -747,7 +756,7 @@ startup_child(char **argv)
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perror_msg_and_die("waitpid");
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}
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if (!WIFSTOPPED(status) || WSTOPSIG(status) != SIGSTOP) {
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kill(pid, SIGKILL);
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kill_save_errno(pid, SIGKILL);
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perror_msg_and_die("Unexpected wait status %x", status);
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}
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}
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@ -757,7 +766,7 @@ startup_child(char **argv)
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*/
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if (ptrace_attach_or_seize(pid)) {
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kill(pid, SIGKILL);
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kill_save_errno(pid, SIGKILL);
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perror_msg_and_die("Can't attach to %d", pid);
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}
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if (!strace_vforked)
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@ -765,9 +774,9 @@ startup_child(char **argv)
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}
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tcp = alloctcb(pid);
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if (!strace_vforked)
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tcp->flags |= TCB_STARTUP | post_attach_sigstop;
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tcp->flags |= TCB_ATTACHED | TCB_STRACE_CHILD | TCB_STARTUP | post_attach_sigstop;
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else
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tcp->flags |= TCB_STARTUP;
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tcp->flags |= TCB_ATTACHED | TCB_STRACE_CHILD | TCB_STARTUP;
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}
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else {
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/* With -D, *we* are child here, IOW: different pid. Fetch it: */
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@ -775,19 +784,9 @@ startup_child(char **argv)
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/* The tracee is our parent: */
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pid = getppid();
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tcp = alloctcb(pid);
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/* We want subsequent startup_attach() to attach to it: */
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tcp->flags |= TCB_ATTACHED;
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}
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}
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static void kill_save_errno(pid_t pid, int sig)
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{
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int saved_errno = errno;
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(void) kill(pid, sig);
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errno = saved_errno;
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}
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/*
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* Test whether the kernel support PTRACE_O_TRACECLONE et al options.
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* First fork a new child, call ptrace with PTRACE_SETOPTIONS on it,
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@ -1440,15 +1439,15 @@ droptcb(struct tcb *tcp)
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}
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/* detach traced process; continue with sig
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Never call DETACH twice on the same process as both unattached and
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attached-unstopped processes give the same ESRCH. For unattached process we
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would SIGSTOP it and wait for its SIGSTOP notification forever. */
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* Never call DETACH twice on the same process as both unattached and
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* attached-unstopped processes give the same ESRCH. For unattached process we
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* would SIGSTOP it and wait for its SIGSTOP notification forever.
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*/
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static int
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detach(struct tcb *tcp)
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{
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int error = 0;
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int status, catch_sigstop;
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int error;
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int status, sigstop_expected;
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if (tcp->flags & TCB_BPTSET)
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clearbpt(tcp);
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@ -1462,31 +1461,36 @@ detach(struct tcb *tcp)
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#undef PTRACE_DETACH
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#define PTRACE_DETACH PTRACE_SUNDETACH
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#endif
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/*
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* We attached but possibly didn't see the expected SIGSTOP.
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* We must catch exactly one as otherwise the detached process
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* would be left stopped (process state T).
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*/
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catch_sigstop = (tcp->flags & TCB_IGNORE_ONE_SIGSTOP);
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error = ptrace(PTRACE_DETACH, tcp->pid, (char *) 1, 0);
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if (error == 0) {
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/* On a clear day, you can see forever. */
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sigstop_expected = 0;
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if (tcp->flags & TCB_ATTACHED) {
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/*
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* We attached but possibly didn't see the expected SIGSTOP.
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* We must catch exactly one as otherwise the detached process
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* would be left stopped (process state T).
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*/
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sigstop_expected = (tcp->flags & TCB_IGNORE_ONE_SIGSTOP);
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error = ptrace(PTRACE_DETACH, tcp->pid, (char *) 1, 0);
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if (error == 0) {
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/* On a clear day, you can see forever. */
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}
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else if (errno != ESRCH) {
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/* Shouldn't happen. */
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perror("detach: ptrace(PTRACE_DETACH, ...)");
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}
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else if (my_tkill(tcp->pid, 0) < 0) {
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if (errno != ESRCH)
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perror("detach: checking sanity");
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}
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else if (!sigstop_expected && my_tkill(tcp->pid, SIGSTOP) < 0) {
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if (errno != ESRCH)
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perror("detach: stopping child");
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}
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else
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sigstop_expected = 1;
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}
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else if (errno != ESRCH) {
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/* Shouldn't happen. */
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perror("detach: ptrace(PTRACE_DETACH, ...)");
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}
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else if (my_tkill(tcp->pid, 0) < 0) {
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if (errno != ESRCH)
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perror("detach: checking sanity");
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}
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else if (!catch_sigstop && my_tkill(tcp->pid, SIGSTOP) < 0) {
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if (errno != ESRCH)
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perror("detach: stopping child");
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}
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else
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catch_sigstop = 1;
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if (catch_sigstop) {
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if (sigstop_expected) {
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for (;;) {
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#ifdef __WALL
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if (wait4(tcp->pid, &status, __WALL, NULL) < 0) {
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@ -1532,7 +1536,7 @@ detach(struct tcb *tcp)
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}
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}
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if (!qflag)
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if (!qflag && (tcp->flags & TCB_ATTACHED))
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fprintf(stderr, "Process %u detached\n", tcp->pid);
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droptcb(tcp);
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@ -1564,7 +1568,7 @@ cleanup(void)
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tprints(" <unfinished ...>\n");
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printing_tcp = NULL;
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}
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if (tcp->flags & TCB_ATTACHED)
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if (!(tcp->flags & TCB_STRACE_CHILD))
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detach(tcp);
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else {
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kill(tcp->pid, SIGCONT);
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@ -2008,7 +2012,8 @@ trace(void)
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* Observed case: exit_group() terminating
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* all processes in thread group.
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*/
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if (tcp->flags & TCB_ATTACHED) {
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if (!(tcp->flags & TCB_STRACE_CHILD)) {
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//TODO: why do we handle our child differently??
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if (printing_tcp) {
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/* Do we have dangling line "syscall(param, param"?
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* Finish the line then.
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