[PATCH 0/3] Fix the O_PATH support for FIFOs

Corinna Vinschen corinna-cygwin@cygwin.com
Fri Jan 24 10:29:00 GMT 2020

On Jan 23 16:31, Ken Brown wrote:
> Commit aa55d22c, "Cygwin: honor the O_PATH flag when opening a FIFO",
> fixed a hang but otherwise didn't accomplish the purpose of the O_PATH
> flag as stated in the Linux man page for open(2):
>     Obtain a file descriptor that can be used for two purposes: to
>     indicate a location in the filesystem tree and to perform
>     operations that act purely at the file descriptor level.  The
>     file itself is not opened, and other file operations (e.g.,
>     read(2), write(2), fchmod(2), fchown(2), fgetxattr(2),
>     ioctl(2), mmap(2)) fail with the error EBADF.
>     [The man page goes on to describe operations that *can* be
>     performed: close(2), fchdir(2), fstat(2),....]
>     Opening a file or directory with the O_PATH flag requires no
>     permissions on the object itself (but does require execute
>     permission on the directories in the path prefix).
> The first problem in the current implementation is that if open(2) is
> called on a FIFO, fhandler_base::device_access_denied is called and
> tries to open the FIFO with read access, which isn't supposed to be
> required.  This is fixed by the first patch in this series.
> The second patch makes fhandler_fifo::open call fhandler_base::open_fs
> if O_PATH is set, so that we actually obtain a handle that can be used
> for the purposes stated above.
> The third page tweaks fhandler_fifo::fcntl and fhandler_fifo::dup so
> that they work with O_PATH.
> In a followup email I'll provide the program I used to test this
> implementation.
> Ken Brown (3):
>   Cygwin: device_access_denied: return false if O_PATH is set
>   Cygwin: re-implement fhandler_fifo::open with O_PATH
>   Cygwin: FIFO: tweak fcntl and dup when O_PATH is set
>  winsup/cygwin/fhandler.cc      |  3 +++
>  winsup/cygwin/fhandler_fifo.cc | 15 ++++++---------
>  2 files changed, 9 insertions(+), 9 deletions(-)
> -- 
> 2.21.0

Pushed.  I'll create new developer snapshots.


Corinna Vinschen
Cygwin Maintainer
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