Factorize killing the children in linux-ptrace.c, and fix a 'process leak'.
Running the gdb testsuite under Valgrind started to fail after 100+ tests, due to out of memory caused by lingering processes. The lingering processes are caused by the combination of a limitation in Valgrind signal handling when using PTRACE_TRACEME and a (minor) bug in GDB. The Valgrind limitation is : when a process is ptraced and raises a signal, Valgrind will replace the raised signal by SIGSTOP as other signals are masked by Valgrind when executing a system call. Removing this limitation seems far to be trivial, valgrind signal handling is very complex. Due to this valgrind limitation, GDB linux_ptrace_test_ret_to_nx gets a SIGSTOP signal instead of the expected SIGTRAP or SIGSEGV. In such a case, linux_ptrace_test_ret_to_nx does an early return, but does not kill the child (running under valgrind), child stays in a STOP-ped state. These lingering processes then eat the available system memory, till launching a new process starts to fail. This patch fixes the GDB minor bug by killing the child in case linux_ptrace_test_ret_to_nx does an early return. nat/linux-ptrace.c has 3 different logics to kill a child process. So, this patch factorizes killing a child in the function kill_child. The 3 different logics are: * linux_ptrace_test_ret_to_nx is calling both kill (child, SIGKILL) and ptrace (PTRACE_KILL, child, ...), and then is calling once waitpid. * linux_check_ptrace_features is calling ptrace (PTRACE_KILL, child, ...) + my_waitpid in a loop, as long as the waitpid status was WIFSTOPPED. * linux_test_for_tracefork is calling once ptrace (PTRACE_KILL, child, ...) + my_waitpid. The linux ptrace documentation indicates that PTRACE_KILL is deprecated, and tells to not use it, as it might return success but not kill the tracee. The documentation indicates to send SIGKILL directly. I suspect that linux_ptrace_test_ret_to_nx calls both kill and ptrace just to be sure ... I suspect that linux_check_ptrace_features calls ptrace in a loop to bypass the PTRACE_KILL limitation. And it looks like linux_test_for_tracefork does not handle the PTRACE_KILL limitation. Also, 2 of the 3 logics are calling my_waitpid, which seems better, as this is protecting the waitpid syscall against EINTR. So, the logic in kill_child is just using kill (child, SIGKILL) + my_waitpid, and then does a few verifications to see everything worked accordingly to the plan. Tested on Debian/x86_64. 2018-12-16 Philippe Waroquiers <philippe.waroquiers@skynet.be> * nat/linux-ptrace.c (kill_child): New function. (linux_ptrace_test_ret_to_nx): Use kill_child instead of local code. Add a call to kill_child in case of early return after fork. (linux_check_ptrace_features): Use kill_child instead of local code. (linux_test_for_tracefork): Likewise.
This commit is contained in:
Philippe Waroquiers
parent
76d2760bc3
commit
a65f68357f
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@ -1,3 +1,11 @@
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2018-12-16 Philippe Waroquiers <philippe.waroquiers@skynet.be>
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* nat/linux-ptrace.c (kill_child): New function.
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(linux_ptrace_test_ret_to_nx): Use kill_child instead of local code.
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Add a call to kill_child in case of early return after fork.
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(linux_check_ptrace_features): Use kill_child instead of local code.
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(linux_test_for_tracefork): Likewise.
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2018-12-14 Tom Tromey <tom@tromey.com>
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* Makefile.in: Remove "alloca" comment.
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@ -79,6 +79,39 @@ EXTERN_C void linux_ptrace_test_ret_to_nx_instr (void);
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#endif /* defined __i386__ || defined __x86_64__ */
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/* Kill CHILD. WHO is used to report warnings. */
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static void
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kill_child (pid_t child, const char *who)
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{
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pid_t got_pid;
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int kill_status;
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if (kill (child, SIGKILL) != 0)
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{
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warning (_("%s: failed to kill child pid %ld %s\n"),
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who, (long) child, safe_strerror (errno));
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return;
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}
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errno = 0;
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got_pid = my_waitpid (child, &kill_status, 0);
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if (got_pid != child)
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{
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warning (_("%s: "
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"kill waitpid returned %ld: %s"),
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who, (long) got_pid, safe_strerror (errno));
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return;
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}
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if (!WIFSIGNALED (kill_status))
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{
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warning (_("%s: "
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"kill status %d is not WIFSIGNALED!"),
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who, kill_status);
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return;
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}
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}
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/* Test broken off-trunk Linux kernel patchset for NX support on i386. It was
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removed in Fedora kernel 88fa1f0332d188795ed73d7ac2b1564e11a0b4cd.
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@ -91,7 +124,7 @@ linux_ptrace_test_ret_to_nx (void)
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pid_t child, got_pid;
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gdb_byte *return_address, *pc;
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long l;
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int status, kill_status;
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int status;
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elf_gregset_t regs;
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return_address
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@ -169,6 +202,7 @@ linux_ptrace_test_ret_to_nx (void)
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{
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warning (_("linux_ptrace_test_ret_to_nx: status %d is not WIFSTOPPED!"),
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status);
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kill_child (child, "linux_ptrace_test_ret_to_nx");
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return;
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}
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@ -178,6 +212,7 @@ linux_ptrace_test_ret_to_nx (void)
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warning (_("linux_ptrace_test_ret_to_nx: "
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"WSTOPSIG %d is neither SIGTRAP nor SIGSEGV!"),
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(int) WSTOPSIG (status));
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kill_child (child, "linux_ptrace_test_ret_to_nx");
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return;
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}
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@ -195,26 +230,7 @@ linux_ptrace_test_ret_to_nx (void)
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# error "!__i386__ && !__x86_64__"
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#endif
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kill (child, SIGKILL);
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ptrace (PTRACE_KILL, child, (PTRACE_TYPE_ARG3) NULL,
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(PTRACE_TYPE_ARG4) NULL);
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errno = 0;
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got_pid = waitpid (child, &kill_status, 0);
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if (got_pid != child)
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{
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warning (_("linux_ptrace_test_ret_to_nx: "
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"PTRACE_KILL waitpid returned %ld: %s"),
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(long) got_pid, safe_strerror (errno));
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return;
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}
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if (!WIFSIGNALED (kill_status))
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{
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warning (_("linux_ptrace_test_ret_to_nx: "
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"PTRACE_KILL status %d is not WIFSIGNALED!"),
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status);
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return;
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}
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kill_child (child, "linux_ptrace_test_ret_to_nx");
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/* + 1 is there as x86* stops after the 'int3' instruction. */
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if (WSTOPSIG (status) == SIGTRAP && pc == return_address + 1)
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@ -352,16 +368,8 @@ linux_check_ptrace_features (void)
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linux_test_for_exitkill (child_pid);
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/* Clean things up and kill any pending children. */
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do
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{
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ret = ptrace (PTRACE_KILL, child_pid, (PTRACE_TYPE_ARG3) 0,
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(PTRACE_TYPE_ARG4) 0);
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if (ret != 0)
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warning (_("linux_check_ptrace_features: failed to kill child"));
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my_waitpid (child_pid, &status, 0);
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}
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while (WIFSTOPPED (status));
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/* Kill child_pid. */
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kill_child (child_pid, "linux_check_ptrace_features");
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}
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/* Determine if PTRACE_O_TRACESYSGOOD can be used to catch
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@ -444,12 +452,7 @@ linux_test_for_tracefork (int child_pid)
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/* Do some cleanup and kill the grandchild. */
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my_waitpid (second_pid, &second_status, 0);
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ret = ptrace (PTRACE_KILL, second_pid, (PTRACE_TYPE_ARG3) 0,
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(PTRACE_TYPE_ARG4) 0);
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if (ret != 0)
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warning (_("linux_test_for_tracefork: "
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"failed to kill second child"));
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my_waitpid (second_pid, &status, 0);
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kill_child (second_pid, "linux_test_for_tracefork");
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}
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}
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else
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