Bug#785189: sendfile stream data corruption

[Eduard Bloch <edi@gmx.de>]

Package: linux-source-3.16
Severity: normal

Hi,

I am not sure how CKT handles bugfix requests but here is something
which is IMHO worth being backported (it actually applies cleanly to
3.16). That problem might explain some of those issues:
https://duckduckgo.com/?q=apt-cacher-ng+hashsum

>From current linux git, master branch:

commit 0ff28d9f4674d781e492bcff6f32f0fe48cf0fed
Author: Christophe Leroy <christophe.leroy@c-s.fr>
Date:   Wed May 6 17:26:47 2015 +0200

    splice: sendfile() at once fails for big files
    
    Using sendfile with below small program to get MD5 sums of some files,
    it appear that big files (over 64kbytes with 4k pages system) get a
    wrong MD5 sum while small files get the correct sum.
    This program uses sendfile() to send a file to an AF_ALG socket
    for hashing.
...
   After investivation, it appears that sendfile() sends the files by blocks
    of 64kbytes (16 times PAGE_SIZE). The problem is that at the end of each
    block, the SPLICE_F_MORE flag is missing, therefore the hashing operation
    is reset as if it was the end of the file.
    
    This patch adds SPLICE_F_MORE to the flags when more data is pending.

Regards,
Eduard.

-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.1.0-rc2.111cputssfix+ (SMP w/4 CPU cores; PREEMPT)
Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash
Init: sysvinit (via /sbin/init)

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