On 01/06/2012 02:47 AM, Joerg Schilling wrote:
Paul Eggert<address@hidden> wrote:
On 01/05/12 14:59, Kamil Dudka wrote:
Is there a known attack on tar that the use of O_NONBLOCK can prevent?
Yes, of course. For example, the attacker can create a
hard link to a fifo while tar is running, which means that
root doing a backup will hang indefinitely.
star does not open FIFO files.....
Yes, it probably does. From your description, it sounds like star is
using a stat() before open() to avoid FIFOs; but this is a classic
TOCTTOU race where an attacker can replace a regular file with a FIFO,
meaning that star will open FIFO files.
Why should gtar open FIFO files?
The question is not why an archiver opens a FIFO file, but what it does
after opening a file O_NONBLOCK (the TOCTTOU race is eliminated by
switching stat()/open() to open()/fstat() filtering, and once we have
ascertained that an open fd is not a FIFO, if we can then use fcntl() to
remove the O_NONBLOCK, hopefully that will resolve the situation with DMF).