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linux-initrd: Gracefully handle lack of or invalid ext2 superblocks. 

Reported by David Thompson <dthompson2@worcester.edu>.

* guix/build/linux-initrd.scm (read-ext2-superblock): Add
  'superblock-size' variable.  Read with 'get-bytevector-n!' instead of
  'getbytevector-n', and make sure we read exactly SUPERBLOCK-SIZE
  bytes.
This commit is contained in:
Ludovic Courtès 2014-07-02 12:18:36 +02:00
parent 0f28ee3487
commit d266b79332
1 changed files with 16 additions and 5 deletions
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21
guix/build/linux-initrd.scm
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@ -116,14 +116,25 @@ if DEVICE does not contain an ext2 file system."
;; The magic bytes that identify an ext2 file system. ;; The magic bytes that identify an ext2 file system.
#xef53) #xef53)
(define superblock-size
;; Size of the interesting part of an ext2 superblock.
264)
(define block
;; The superblock contents.
(make-bytevector superblock-size))
(call-with-input-file device (call-with-input-file device
(lambda (port) (lambda (port)
(seek port 1024 SEEK_SET) (seek port 1024 SEEK_SET)
(let* ((block (get-bytevector-n port 264))
(magic (bytevector-u16-ref block %ext2-sblock-magic ;; Note: work around <http://bugs.gnu.org/17466>.
%ext2-endianness))) (and (eqv? superblock-size (get-bytevector-n! port block 0
(and (= magic %ext2-magic) superblock-size))
block))))) (let ((magic (bytevector-u16-ref block %ext2-sblock-magic
%ext2-endianness)))
(and (= magic %ext2-magic)
block))))))
(define (ext2-superblock-uuid sblock) (define (ext2-superblock-uuid sblock)
"Return the UUID of ext2 superblock SBLOCK as a 16-byte bytevector." "Return the UUID of ext2 superblock SBLOCK as a 16-byte bytevector."