[Bug 1594394] Re: Using setreuid / setegid crashes x86_64 user-mode target

[Thomas Huth]

The QEMU project is currently considering to move its bug tracking to
another system. For this we need to know which bugs are still valid
and which could be closed already. Thus we are setting older bugs to
"Incomplete" now.

If you still think this bug report here is valid, then please switch
the state back to "New" within the next 60 days, otherwise this report
will be marked as "Expired". Or please mark it as "Fix Released" if
the problem has been solved with a newer version of QEMU already.

Thank you and sorry for the inconvenience.

** Changed in: qemu
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1594394

Title:
  Using setreuid / setegid crashes x86_64 user-mode target

Status in QEMU:
  Incomplete

Bug description:
  When setreuid() or setegid() are called from x86_64 target code in
  user mode, qemu crashes inside the NPTL signal handlers.  x86 targets
  do not directly use a syscall to handle setreuid() / setegid();
  instead the x86 NPTL implementation sets up a temporary data region in
  memory (__xidcmd) and issues a signal (SIGRT1) to all threads,
  allowing the handler for that signal to issue the syscall.  Under
  qemu, __xidcmd remains null (see variable display below backtrace).

  Backtrace:
  Program received signal SIGSEGV, Segmentation fault.
  [Switching to Thread 0x3fff85c74fc0 (LWP 74517)]
  0x000000006017491c in sighandler_setxid (sig=33, si=0x3fff85c72d08, 
ctx=0x3fff85c71f90) at nptl-init.c:263
  263     nptl-init.c: No such file or directory.
  (gdb) thread apply all bt

  Thread 3 (Thread 0x3fff87e8efc0 (LWP 74515)):
  #0  0x00000000601cc430 in syscall ()
  #1  0x0000000060109080 in futex_wait (val=<optimized out>, ev=<optimized 
out>) at /build/qemu/util/qemu-thread-posix.c:292
  #2  qemu_event_wait (ev=0x62367bb0 <rcu_call_ready_event>) at 
/build/qemu/util/qemu-thread-posix.c:399
  #3  0x000000006010f73c in call_rcu_thread (opaque=<optimized out>) at 
/build/qemu/util/rcu.c:250
  #4  0x0000000060176f8c in start_thread (arg=0x3fff87e8efc0) at 
pthread_create.c:336
  #5  0x00000000601cebf4 in clone ()

  Thread 2 (Thread 0x3fff85c74fc0 (LWP 74517)):
  #0  0x000000006017491c in sighandler_setxid (sig=33, si=0x3fff85c72d08, 
ctx=0x3fff85c71f90) at nptl-init.c:263
  #1  <signal handler called>
  #2  0x00000000601cc42c in syscall ()
  #3  0x0000000060044b08 in safe_futex (val3=<optimized out>, uaddr2=0x0, 
timeout=<optimized out>, val=<optimized out>, op=128, uaddr=<optimized out>) at 
/build/qemu/linux-user/syscall.c:748
  #4  do_futex (val3=<optimized out>, uaddr2=275186650880, timeout=0, val=1129, 
op=128, uaddr=275186651116) at /build/qemu/linux-user/syscall.c:6201
  #5  do_syscall (cpu_env=0x1000abfd350, num=<optimized out>, 
arg1=275186651116, arg2=<optimized out>, arg3=1129, arg4=0, arg5=275186650880, 
arg6=<optimized out>, arg7=0, arg8=0)
      at /build/qemu/linux-user/syscall.c:10651
  #6  0x00000000600347b8 in cpu_loop (env=0x1000abfd350) at 
/build/qemu/linux-user/main.c:317
  #7  0x0000000060036ae0 in clone_func (arg=0x3fffc4c2ca38) at 
/build/qemu/linux-user/syscall.c:5445
  #8  0x0000000060176f8c in start_thread (arg=0x3fff85c74fc0) at 
pthread_create.c:336
  #9  0x00000000601cebf4 in clone ()

  Thread 1 (Thread 0x1000aa05000 (LWP 74511)):
  #0  0x00000000601cc430 in syscall ()
  #1  0x0000000060044b08 in safe_futex (val3=<optimized out>, uaddr2=0x0, 
timeout=<optimized out>, val=<optimized out>, op=128, uaddr=<optimized out>) at 
/build/qemu/linux-user/syscall.c:748
  #2  do_futex (val3=<optimized out>, uaddr2=1, timeout=0, val=1, op=128, 
uaddr=275078324992) at /build/qemu/linux-user/syscall.c:6201
  #3  do_syscall (cpu_env=0x1000aa23890, num=<optimized out>, 
arg1=275078324992, arg2=<optimized out>, arg3=1, arg4=0, arg5=1, 
arg6=<optimized out>, arg7=0, arg8=0) at /build/qemu/linux-user/syscall.c:10651
  #4  0x00000000600347b8 in cpu_loop (env=0x1000aa23890) at 
/build/qemu/linux-user/main.c:317
  #5  0x00000000600020e4 in main (argc=<optimized out>, argv=<optimized out>, 
envp=<optimized out>) at /build/qemu/linux-user/main.c:4779
  (gdb) p __xidcmd
  $1 = (struct xid_command *) 0x0

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