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zlib: Fix race condition when closing gzip ports.

Fixes <>.

* guix/zlib.scm (close-procedure): Remove.
(make-gzip-input-port): Do (dup (fileno port)) to get a file descriptor
for 'gzdopen'.  Close PORT before returning.  Use 'gzclose' as the
'close' procedure of the returned port.
(make-gzip-output-port): Likewise.
Ludovic Courtès 4 years ago
No known key found for this signature in database GPG Key ID: 90B11993D9AEBB5
  1. 46


@ -1,5 +1,5 @@
;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2016 Ludovic Courtès <>
;;; Copyright © 2016, 2017 Ludovic Courtès <>
;;; This file is part of GNU Guix.
@ -149,31 +149,6 @@ the number of uncompressed bytes written, a strictly positive integer."
(define (close-procedure gzfile port)
"Return a procedure that closes GZFILE, ensuring its underlying PORT is
closed even if closing GZFILE triggers an exception."
(let-syntax ((ignore-EBADF
(syntax-rules ()
((_ exp)
(catch 'system-error
(lambda ()
(lambda args
(unless (= EBADF (system-error-errno args))
(apply throw args))))))))
(lambda ()
(catch 'zlib-error
(lambda ()
;; 'gzclose' closes the underlying file descriptor. 'close-port'
;; calls close(2) and gets EBADF, which we swallow.
(gzclose gzfile)
(ignore-EBADF (close-port port)))
(lambda args
;; Make sure PORT is closed despite the zlib error.
(ignore-EBADF (close-port port))
(apply throw args))))))
(define* (make-gzip-input-port port #:key (buffer-size %default-buffer-size))
"Return an input port that decompresses data read from PORT, a file port.
PORT is automatically closed when the resulting port is closed. BUFFER-SIZE
@ -183,7 +158,14 @@ buffered input, which would be lost (and is lost anyway)."
(define gzfile
(match (drain-input port)
("" ;PORT's buffer is empty
(gzdopen (fileno port) "r"))
;; 'gzclose' will eventually close the file descriptor beneath PORT.
;; 'close-port' on PORT would get EBADF if 'gzclose' already closed it,
;; so that's no good; revealed ports are no good either because they
;; leak (see <>); calling 'close-port' after
;; 'gzclose' doesn't work either because it leads to a race condition
;; (see <>). So we dup and close PORT right
;; away.
(gzdopen (dup (fileno port)) "r"))
;; This is unrecoverable but it's better than having the buffered input
;; be lost, leading to unclear end-of-file or corrupt-data errors down
@ -197,8 +179,10 @@ buffered input, which would be lost (and is lost anyway)."
(unless (= buffer-size %default-buffer-size)
(gzbuffer! gzfile buffer-size))
(close-port port) ;we no longer need it
(make-custom-binary-input-port "gzip-input" read! #f #f
(close-procedure gzfile port)))
(lambda ()
(gzclose gzfile))))
(define* (make-gzip-output-port port
@ -210,7 +194,7 @@ port is closed."
(define gzfile
(force-output port) ;empty PORT's buffer
(gzdopen (fileno port)
(gzdopen (dup (fileno port))
(string-append "w" (number->string level)))))
(define (write! bv start count)
@ -219,8 +203,10 @@ port is closed."
(unless (= buffer-size %default-buffer-size)
(gzbuffer! gzfile buffer-size))
(close-port port)
(make-custom-binary-output-port "gzip-output" write! #f #f
(close-procedure gzfile port)))
(lambda ()
(gzclose gzfile))))
(define* (call-with-gzip-input-port port proc
#:key (buffer-size %default-buffer-size))