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authorLudovic Courtès <ludo@gnu.org>2017-01-31 21:52:46 +0100
committerLudovic Courtès <ludo@gnu.org>2017-01-31 23:21:59 +0100
commit2fe4ceee18f8687de8520d28dbfefc7bc3a7e084 (patch)
tree7c5e4ebcbc688ccf2ec00cf6a937db32f698a376
parent69f2b3bdf9ca333a09995d5006d78f83bb417968 (diff)
downloadgnu-guix-2fe4ceee18f8687de8520d28dbfefc7bc3a7e084.tar
gnu-guix-2fe4ceee18f8687de8520d28dbfefc7bc3a7e084.tar.gz
file-systems: Do not read superblocks past the end of a device.
Fixes <http://bugs.gnu.org/25573>. Reported by Alex Kost <alezost@gmail.com>. * gnu/build/file-systems.scm (seek*): New procedure. (read-superblock): Use it instead of 'seek' and ensure it returns OFFSET.
-rw-r--r--gnu/build/file-systems.scm33
1 files changed, 22 insertions, 11 deletions
diff --git a/gnu/build/file-systems.scm b/gnu/build/file-systems.scm
index 6e5c6aaf15..f8ab95370c 100644
--- a/gnu/build/file-systems.scm
+++ b/gnu/build/file-systems.scm
@@ -1,5 +1,5 @@
;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2014, 2015, 2016 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2014, 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2016, 2017 David Craven <david@craven.ch>
;;;
;;; This file is part of GNU Guix.
@@ -72,22 +72,33 @@
"Bind-mount SOURCE at TARGET."
(mount source target "" MS_BIND))
+(define (seek* fd/port offset whence)
+ "Like 'seek' but return -1 instead of throwing to 'system-error' upon
+EINVAL. This makes it easier to catch cases like OFFSET being too large for
+FD/PORT."
+ (catch 'system-error
+ (lambda ()
+ (seek fd/port offset whence))
+ (lambda args
+ (if (= EINVAL (system-error-errno args))
+ -1
+ (apply throw args)))))
+
(define (read-superblock device offset size magic?)
"Read a superblock of SIZE from OFFSET and DEVICE. Return the raw
superblock on success, and #f if no valid superblock was found. MAGIC?
takes a bytevector and returns #t when it's a valid superblock."
(call-with-input-file device
(lambda (port)
- (seek port offset SEEK_SET)
-
- (let ((block (make-bytevector size)))
- (match (get-bytevector-n! port block 0 (bytevector-length block))
- ((? eof-object?)
- #f)
- ((? number? len)
- (and (= len (bytevector-length block))
- (and (magic? block)
- block))))))))
+ (and (= offset (seek* port offset SEEK_SET))
+ (let ((block (make-bytevector size)))
+ (match (get-bytevector-n! port block 0 (bytevector-length block))
+ ((? eof-object?)
+ #f)
+ ((? number? len)
+ (and (= len (bytevector-length block))
+ (and (magic? block)
+ block)))))))))
(define (sub-bytevector bv start size)
"Return a copy of the SIZE bytes of BV starting from offset START."