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 9/6/2020 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.

I think fhandler_process::exists is not doing the right thing here, but I'm not 
familiar with this part of the code, so I'll have to stare at it for a while to 
see what's going wrong.

Corinna, if you are able to see it more quickly and want to go ahead and fix it, 
you won't hurt my feelings.

Ken