[Pkg-samba-maint] Bug#699461: /usr/sbin/smbd: Data corruption / file truncation not working with "large readwrite" set to "no"

[Tobias Vogel]

Package: samba
Version: 2:3.5.6~dfsg-3squeeze8
Severity: important
File: /usr/sbin/smbd


On a debian default install of samba, when setting the parameter "large readwrite" to "no" (which is often recommended by users in some wikis / blogs / communities), file truncation will not happen when rewriting / saving the file. When the new content's size is smaller than the old one, trailing garbage is left at the end and thus leaving a corrupted file on the disk.

This bug may also affect upstream samba, as another user with a NAS experienced the same behaviour:
http://stackoverflow.com/questions/12211629/php-file-put-contents-not-truncating-file-in-cifs-mount


Test script to reproduce the behaviour:

echo "thisisabigfatpandaonwheelsgoingdownthestreet" > /mnt/test/newfile.txt
cat /mnt/test/newfile.txt

=> thisisabigfatpandaonwheelsgoingdownthestreet

echo -n "blah" > /mnt/test/newfile.txt
cat /mnt/test/newfile.txt

=> blahisabigfatpandaonwheelsgoingdownthestreet

Expected output of the second cat command:

=> blah


Changes to default smb.conf:

diff -pruN /usr/share/samba/smb.conf /etc/samba/smb.conf
--- /usr/share/samba/smb.conf   2012-04-30 08:53:47.000000000 +0200
+++ /etc/samba/smb.conf 2013-01-31 16:51:24.000000000 +0100
@@ -31,6 +31,7 @@
 #======================= Global Settings =======================

 [global]
+   large readwrite = no

 ## Browsing/Identification ###

@@ -323,3 +324,9 @@
 ;   preexec = /bin/mount /cdrom
 ;   postexec = /bin/umount /cdrom

+[test]
+   writable = yes
+   path = /export/test
+   valid users = testuser
+   create mask = 0644
+   guest ok = no


Mount on the test client:

//smbserver/test /mnt/test        cifs    rw,user=testuser,passwd=xxx 0 0


-- System Information:
Debian Release: 6.0.6
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.32-5-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages samba depends on:
ii  adduser           3.112+nmu2             add and remove users and groups
ii  debconf [debconf- 1.5.36.1               Debian configuration management sy
ii  libacl1           2.2.49-4               Access control list shared library
ii  libattr1          1:2.4.44-2             Extended attribute shared library
ii  libc6             2.11.3-4               Embedded GNU C Library: Shared lib
ii  libcap2           1:2.19-3               support for getting/setting POSIX.
ii  libcomerr2        1.41.12-4stable1       common error description library
ii  libcups2          1.4.4-7+squeeze2       Common UNIX Printing System(tm) - 
ii  libgssapi-krb5-2  1.8.3+dfsg-4squeeze6   MIT Kerberos runtime libraries - k
ii  libk5crypto3      1.8.3+dfsg-4squeeze6   MIT Kerberos runtime libraries - C
ii  libkrb5-3         1.8.3+dfsg-4squeeze6   MIT Kerberos runtime libraries
ii  libldap-2.4-2     2.4.23-7.2             OpenLDAP libraries
ii  libpam-modules    1.1.1-6.1+squeeze1     Pluggable Authentication Modules f
ii  libpam-runtime    1.1.1-6.1+squeeze1     Runtime support for the PAM librar
ii  libpam0g          1.1.1-6.1+squeeze1     Pluggable Authentication Modules l
ii  libpopt0          1.16-1                 lib for parsing cmdline parameters
ii  libtalloc2        2.0.1-1                hierarchical pool based memory all
ii  libwbclient0      2:3.5.6~dfsg-3squeeze8 Samba winbind client library
ii  lsb-base          3.2-23.2squeeze1       Linux Standard Base 3.2 init scrip
ii  procps            1:3.2.8-9squeeze1      /proc file system utilities
ii  samba-common      2:3.5.6~dfsg-3squeeze8 common files used by both the Samb
ii  update-inetd      4.38+nmu1+squeeze1     inetd configuration file updater
ii  zlib1g            1:1.2.3.4.dfsg-3       compression library - runtime

Versions of packages samba recommends:
ii  logrotate                     3.7.8-6    Log rotation utility

Versions of packages samba suggests:
pn  ctdb                          <none>     (no description available)
pn  ldb-tools                     <none>     (no description available)
pn  openbsd-inetd | inet-superser <none>     (no description available)
pn  smbldap-tools                 <none>     (no description available)

-- debconf information:
  samba/run_mode: daemons
  samba/generate_smbpasswd: true