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procdesc: fix reparenting when the debugger is attached

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The process is reparented to the debugger while it is attached.
  B          B
 /   ---->   |
A          A D

Every time when the process is reparented, it is added to the orphan list
of the previous parent:

A->orphan = B
D->orphan = NULL

When the A process will close the process descriptor to the B process,
the B process will be reparented to the init process.
  B            B - init
  |   ---->
A D          A   D

A->orphan = B
D->orphan = B

In this scenario, the B process is in the orphan list of A and D.

When the last process descriptor is closed instead of reparenting
it to the reaper let it stay with the debugger process and set
our previews parent to the reaper.

Add test case for this situation.
Notice that without this patch the kernel will crash with this test case:
panic: orphan 0xfffff8000e990530 of 0xfffff8000e990000 has unexpected oppid 1

Reviewed by:	markj, kib
MFC after:	1 month
Differential Revision:	https://reviews.freebsd.org/D20361
This commit is contained in:
Mariusz Zaborski 2019-08-05 20:15:46 +00:00
parent 799d92ab78
commit fd631bcd95
2 changed files with 63 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
sys/kern/sys_procdesc.c
View File

@ -416,7 +416,13 @@ procdesc_close(struct file *fp, struct thread *td)
* terminate with prejudice.
*/
p->p_sigparent = SIGCHLD;
proc_reparent(p, p->p_reaper, true);
if ((p->p_flag & P_TRACED) == 0) {
proc_reparent(p, p->p_reaper, true);
} else {
clear_orphan(p);
p->p_oppid = p->p_reaper->p_pid;
proc_add_orphan(p, p->p_reaper);
}
if ((pd->pd_flags & PDF_DAEMON) == 0)
kern_psignal(p, SIGKILL);
PROC_UNLOCK(p);

56
tests/sys/kern/ptrace_test.c
View File

@ -32,6 +32,7 @@ __FBSDID("$FreeBSD$");
#include <sys/file.h>
#include <sys/time.h>
#include <sys/procctl.h>
#include <sys/procdesc.h>
#include <sys/ptrace.h>
#include <sys/queue.h>
#include <sys/runq.h>
@ -4075,6 +4076,60 @@ ATF_TC_BODY(ptrace__syscall_args, tc)
ATF_REQUIRE(errno == ECHILD);
}
/*
* Verify that when the process is traced that it isn't reparent
* to the init process when we close all process descriptors.
*/
ATF_TC(ptrace__proc_reparent);
ATF_TC_HEAD(ptrace__proc_reparent, tc)
{
atf_tc_set_md_var(tc, "timeout", "2");
}
ATF_TC_BODY(ptrace__proc_reparent, tc)
{
pid_t traced, debuger, wpid;
int pd, status;
traced = pdfork(&pd, 0);
ATF_REQUIRE(traced >= 0);
if (traced == 0) {
raise(SIGSTOP);
exit(0);
}
ATF_REQUIRE(pd >= 0);
debuger = fork();
ATF_REQUIRE(debuger >= 0);
if (debuger == 0) {
/* The traced process is reparented to debuger. */
ATF_REQUIRE(ptrace(PT_ATTACH, traced, 0, 0) == 0);
wpid = waitpid(traced, &status, 0);
ATF_REQUIRE(wpid == traced);
ATF_REQUIRE(WIFSTOPPED(status));
ATF_REQUIRE(WSTOPSIG(status) == SIGSTOP);
ATF_REQUIRE(close(pd) == 0);
ATF_REQUIRE(ptrace(PT_DETACH, traced, (caddr_t)1, 0) == 0);
/* We closed pd so we should not have any child. */
wpid = wait(&status);
ATF_REQUIRE(wpid == -1);
ATF_REQUIRE(errno == ECHILD);
exit(0);
}
ATF_REQUIRE(close(pd) == 0);
wpid = waitpid(debuger, &status, 0);
ATF_REQUIRE(wpid == debuger);
ATF_REQUIRE(WEXITSTATUS(status) == 0);
/* Check if we still have any child. */
wpid = wait(&status);
ATF_REQUIRE(wpid == -1);
ATF_REQUIRE(errno == ECHILD);
}
ATF_TP_ADD_TCS(tp)
{
@ -4137,6 +4192,7 @@ ATF_TP_ADD_TCS(tp)
#endif
ATF_TP_ADD_TC(tp, ptrace__PT_LWPINFO_stale_siginfo);
ATF_TP_ADD_TC(tp, ptrace__syscall_args);
ATF_TP_ADD_TC(tp, ptrace__proc_reparent);
return (atf_no_error());
}