Postfix chroot and libresolv

[lazyfrosch]

I noticed something odd with chroot detection for libraries.

Apparently postfix has the libresolv library already opened, and hands that off to its childs.

Therefore the opened inode is not the one in the chroot.

Debian: stretch
needrestart: 85b172f (master)

$ ps -ef | grep pickup
postfix  16130 13617  0 19:08 ?        00:00:00 pickup -l -t unix -u -c

$ sudo cat /proc/16130/maps | grep resolv
7fd1b6757000-7fd1b676b000 r-xp 00000000 fe:01 264409                     /lib/x86_64-linux-gnu/libresolv-2.19.so
7fd1b676b000-7fd1b696a000 ---p 00014000 fe:01 264409                     /lib/x86_64-linux-gnu/libresolv-2.19.so
7fd1b696a000-7fd1b696b000 r--p 00013000 fe:01 264409                     /lib/x86_64-linux-gnu/libresolv-2.19.so
7fd1b696b000-7fd1b696c000 rw-p 00014000 fe:01 264409                     /lib/x86_64-linux-gnu/libresolv-2.19.so

$ stat /lib/x86_64-linux-gnu/libresolv-2.19.so
  File: ‘/lib/x86_64-linux-gnu/libresolv-2.19.so’
  Size: 84856       Blocks: 168        IO Block: 4096   regular file
Device: fe01h/65025d    Inode: 264409      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2015-08-12 20:55:01.804832072 +0200
Modify: 2015-07-09 15:28:33.000000000 +0200
Change: 2015-07-23 15:39:20.373921081 +0200
 Birth: -

$ stat /var/spool/postfix//lib/x86_64-linux-gnu/libresolv-2.19.so
  File: ‘/var/spool/postfix//lib/x86_64-linux-gnu/libresolv-2.19.so’
  Size: 84856       Blocks: 168        IO Block: 4096   regular file
Device: fe01h/65025d    Inode: 655099      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2015-08-13 19:09:00.292981313 +0200
Modify: 2015-07-09 15:28:33.000000000 +0200
Change: 2015-08-13 18:49:48.261795689 +0200
 Birth: -

[liske]

Hi,

I'm not an expert on postfix... do you know how the lib files get into /var/spool/postfix/lib ? They seem to be not part of a package (just verified on a jessie box):

$ dpkg -S /var/spool/postfix/lib/x86_64-linux-gnu/libresolv-2.13.so 
dpkg-query: no path found matching pattern /var/spool/postfix/lib/x86_64-linux-gnu/libresolv-2.13.so

[lazyfrosch]

Postfix is running in a chroot jail on Debian by default. The Initscript takes care about deploying those files on every start.

It might help if we compare files inside a chroot to outside of a chroot. Makes that sense? Or remove the chroot to maybe find the file outside?

[liske]

Although needrestart did check if a library exists within the root of the process (/proc/$PID/root/$path) or the root of needrestart (just /$path), it has failed if both paths exist. If /proc/$PID/root/$path exist it was always preferred while comparing the device and inode values.

The code has been improved to check both paths if both does exist.