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 9/7/2020 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.

Thanks for reporting the problem.

Ken