Re: File watching

[Michael C Thompson <thompsmc@us.ibm.com>]

Timothy R. Chavez wrote:
> On Tue, 2006-06-20 at 14:32 -0400, Steve wrote:
>>>> Instead, you audit the file open, and make a note of whether the file
>>>> was opened read-only, or for read/write.  If it was opened for
>>>> read/write, one presumes that it was written to.
>> Is it possible to tell if a file was opened read/write or read-only from 
>> the events generated by audit?
>>
>> Thanks,
>> Steve
> 
> Hi Steve,
> 
> You should be able to ascertain this information from the open() audit
> record.  I thought at one time the flags were recorded in the record,
> but perhaps no longer (or maybe my memory does not serve me well :)).
> The record does record syscall arguments, however, so perhaps you could
> analyze a1= (I believe this is the argument that passes flags), and
> figure out with what flags open() was called with.  Admittedly, I'm not
> so knowledgeable these days as to what is actually being reported in the
> audit log.

Tim,

You are correct, the associated meaning for a1 with the open syscall is 
flags [ http://www.linux-m32r.org/lxr/http/source/fs/open.c#L1100 ].

In the following example open() syscall record, you can see a1 is 0x8000.
type=SYSCALL msg=audit(1150567434.940:1386): arch=40000003 syscall=5 
success=yes exit=3 a0=93bd6e0 a1=8241 a2=1b6 a3=8241 items=2 ppid=2106 
pid=2108 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 
tty=pts1 comm="bash" exe="/bin/bash" 
subj=root:staff_r:staff_t:s0-s15:c0.c255

a0 -- pointer, not useful
s1 -- the flags used for creation, in this case 0x8241 -> O_WRONLY | 
O_CREAT | O_TRUNC | O_LARGEFILE
a2 -- the mode, in this case 0x1b6 -> 0666

http://www.linux-m32r.org/lxr/http/source/include/asm-generic/fcntl.h#L7

Can you guess what simple shell command I used to get this log? :P

Thanks,
Mike