/dev/fd/N not synonymous with file descriptor N; it is on Linux

[Corinna Vinschen]

On Jan 22 09:50, Houder wrote:
> On Sun, 6 Jan 2019 21:19:50, Corinna Vinschen  wrote:
> > > Also see:
> > >
> > >     https://cygwin.com/ml/cygwin/2018-12/msg00028.html
> > >     ( Bash heredoc on FD 3 )
> > >
> > > Based on the output of strace on Linux, I composed an STC, that duplicates
> > > the steps taken by bash (and cat).
> > 
> > This should work in the latest developer snapshot uploaded to
> > https://cygwin.com/snapshots/  Please give it a try.
> 
> This solves: <program> -i /dev/fd/N N<<EOF (i.e. Steven Penny's problem)
> 
> Howver ...
> (and I sure that I am not telling you anything new)
> [...]
> 64-@@ rm aap.txt # hacker removing the logfile
> 
> 64-@@ stat -L /proc/4120/fd/3
>   File: /proc/4120/fd/3
>   Size: 4               Blocks: 1          IO Block: 65536  regular file
> Device: 33d91880h/869865600d    Inode: 35747322042382612  Links: 0
> Access: (0644/-rw-r--r--)  Uid: ( 1000/   Henri)   Gid: (  513/    None)
> Access: 2019-01-22 09:24:41.978178200 +0100
> Modify: 2019-01-22 09:24:41.978178200 +0100
> Change: 2019-01-22 09:26:25.021040800 +0100
>  Birth: 2019-01-22 09:24:41.978178200 +0100
> 
> 64-@@ cp /proc/4120/fd/3 noot.txt # logfile rescue
> 64-@@ cat noot.txt # empty! (however, this works on Linux)
> 64-@@ cat /proc/4120/fd/3 # indeed, does not show contents
> 64-@@

Yes, this does not work under older systems.  However, it works as
desired at least with Windows 10 1709 due to changes in the OS in
terms of handling of deleted files.

I tested this with W8.1, W10 1709 and W10 1809.  It fails on 8.1
but works fine on both W10 versions.


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
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