ag 2 <(echo 2) gets assertion "p >= path" failed: .. /cygwin-3.1.7 ... /cygwin/path.cc", line 3065, function: int symlink_info::check

[Ken Brown]

On 9/8/2020 3:26 PM, Ken Brown via Cygwin wrote:
> On 9/7/2020 4:35 PM, Ken Brown via Cygwin wrote:
>> On 9/6/2020 4:28 PM, Ken Brown via Cygwin wrote:
>>> On 9/6/2020 3:47 PM, Ken Brown via Cygwin wrote:
>>>> On 9/6/2020 2:43 PM, David Dyck via Cygwin wrote:
>>>>> This command triggers an assertion failure
>>>>>    "ag" is from the_silver_searcher
>>>>>
>>>>> $ ag 2 <(echo 2)
>>>>> assertion "p >= path" failed: file
>>>>> "/home/corinna/src/cygwin/cygwin-3.1.7/cygwin-3.1.7-1.x86_64/src/newlib-cygwin/winsup/cygwin/path.cc", 
>>>>>
>>>>> line 3065, function: int symlink_info::check(char*, const
>>>>> suffix_info*, fs_info&, path_conv_handle&)
>>>>> Aborted (core dumped)
>>>>>
>>>>>   3473k 2020/08/22 C:\cygwin64\bin\cygwin1.dll
>>>>>      Cygwin DLL version info:
>>>>>          DLL version: 3.1.7
>>>>> bash                                    4.4.12-3                        OK
>>>>> the_silver_searcher                     2.2.0-1                         OK
>>>> [...]
>>>>> assertion "p >= path" failed: file
>>>>> "/home/corinna/src/cygwin/cygwin-3.1.7/cygwin-3.1.7-1.x86_64/src/newlib-cygwin/winsup/cygwin/path.cc", 
>>>>>
>>>>> line 3065, function: int symlink_info::check(char*, const
>>>>> suffix_info*, fs_info&, path_conv_handle&)
>>>>> Aborted (core dumped)
>>>> [...]
>>>>> I've reported this on github as an "ag" bug, but I think it is a bug in cygwin
>>>>
>>>> An assertion failure in Cygwin code is a Cygwin bug.  I'll take a look.
>>>
>>> Running
>>>
>>>    bash -c '/usr/bin/ag 2 <(echo 2)'
>>>
>>> under strace yields the following:
>>>
>>>    242  191767 [main] ag 33659 open: open(/dev/fd/63/.ignore, 0x0)
>>> [...]
>>>     30  192584 [main] ag 33659 mount_info::conv_to_win32_path: src_path 
>>> /proc/self/fd/63/.ignore, dst /proc/self/fd/63/.ignore, flags 0x0, rc 0
>>> [...]
>>>     31  193366 [main] ag 33659 mount_info::conv_to_win32_path: 
>>> conv_to_win32_path (pipe:[4295036184]/.ignore)
>>> [...]
>>>     31  193550 [main] ag 33659 mount_info::conv_to_win32_path: 
>>> conv_to_win32_path (pipe:[4295036184])
>>> [...]
>>>     34  193615 [main] ag 33659 symlink_info::check: 0xC0000034 = NtCreateFile 
>>> (\??\C:pipe:[4295036184])
>>>
>>> The assertion fails because the path 'C:pipe:[4295036184]' doesn't contain a 
>>> backslash.  But probably we should never have allowed ourselves to get to the 
>>> point of considering that path.
>>
>> I've made some progress but haven't figured out the fix yet.  First, for 
>> easier debugging, here's a simpler way to reproduce the problem:
>>
>> $ cat proc_bug.c
>> #include <unistd.h>
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <fcntl.h>
>>
>> int
>> main ()
>> {
>>    int fd[2];
>>    char fname[100];
>>
>>    if (pipe (fd) < 0)
>>      {
>>        perror ("pipe");
>>        exit (1);
>>      }
>>    sprintf (fname, "/dev/fd/%d/foo", fd[0]);
>>    if (open (fname, O_RDONLY) < 0)
>>      {
>>        perror ("open");
>>        exit (1);
>>      }
>> }
>>
>> $ gcc -o proc_bug proc_bug.c
>>
>> $ ./proc_bug.exe
>> assertion "p >= path" failed: file 
>> "../../../../newlib-cygwin/winsup/cygwin/path.cc", line 3065, function: int 
>> symlink_info::check(char*, const suffix_info*, fs_info&, path_conv_handle&)
>> Aborted (core dumped)
>>
>> Here's what happens.  The program is trying to open /dev/fd/3/foo, where file 
>> descriptor 3 is the read end of a pipe.  path_conv check resolves this to 
>> /proc/<pid>/fd/3/foo, creates an fhandler_process for this path, and calls (at 
>> path.cc:782) fhandler_process::exists.  The latter fills the filebuf with 
>> "pipe:[xxxxxxxxxx]/foo" and returns virt_fsdir.  We're now at path.cc:808, and 
>> everything is set up for the assertion failure.
> 
> This is now fixed.  David, you can test it as soon as Corinna has a chance to 
> make a new Cygwin snapshot.

That's now done:

   https://cygwin.com/snapshots/

Ken