Re: [RFC] breakage in sysfs_readdir() and s_instances abuse in sysfs

On Sun, Jun 05, 2011 at 06:55:12AM +0900, Linus Torvalds wrote:

On Sun, Jun 5, 2011 at 6:22 AM, Al Viro [off-list ref] wrote:

quoted

Are you OK with the sketch above? ?I can probably cook a patch along those
lines by tomorrow...

I'm ok with the sketch, but might think otherwise when actually seeing
the patch. And I wish some namespace person would look at this issue.
And the networking people would seem to need to be aware of it too,
but you've only cc'd fsdevel, so they are entirely unaware of the
whole thread..

Eh...  The question had been to Eric, unless that pile is actually yours...
netdev Cc'd, and I'll forward the previous posting there in a few.

FWIW, reproducing that is trivial: on a box with netns enabled:

dizzy:~# unshare -n -- sh -c "mount -t sysfs none /mnt; ls -l /mnt/class/net; ls
 -l /mnt/class/net/eth0"                                                        
[ 1301.429755] IPv4 FIB: Using LC-trie version 0.409                            
total 0                                                                         
lrwxrwxrwx 1 root root 0 Jun  4 18:16 lo -> ../../devices/virtual/net/lo        
lrwxrwxrwx 1 root root 0 Jun  4 18:16 sit0 -> ../../devices/virtual/net/sit0    
ls: cannot access /mnt/class/net/eth0: No such file or directory                
dizzy:~# ls -l /mnt/class/net/; ls -l /mnt/class/net/eth0                       
total 0                                                                         
lrwxrwxrwx 1 root root 0 Jun  4 18:17 /mnt/class/net/eth0 -> ../../devices/pci00
00:00/0000:00:09.0/net/eth0                                                     

IOW, while netns is alive we get sane behaviour - lookup for class/net/eth0
fails, since there's no such object in that netns.  Once it's gone, we get
class/net in that sysfs instance empty on readdir *and* lookup for
class/net/eth0 succeeds giving us an object from another netns.

Apologies for not adding netdev - it started as sysfs-internal race, so the
beginning of that thread went to fsdevel...