Messages in this thread | | | From | (Eric W. Biederman) | Date | Fri, 11 Jul 2008 20:42:51 -0700 | Subject | Re: [PATCH 9/12] ipv4: assign PDE->data before gluing PDE into /proc tree |
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"Stoyan Gaydarov" <stoyboyker@gmail.com> writes:
> First off, sorry to bring such an old email back but I can seem to get > a bad feeling when looking back over it. > > On Tue, Apr 29, 2008 at 6:13 AM, Denis V. Lunev <den@openvz.org> wrote: >> The check for PDE->data != NULL becomes useless after the replacement >> of proc_net_fops_create with proc_create_data. >> >> Signed-off-by: Denis V. Lunev <den@openvz.org> >> Cc: Alexey Dobriyan <adobriyan@openvz.org> >> Cc: Eric W. Biederman <ebiederm@xmission.com> >> Cc: David S. Miller <davem@davemloft.net> >> --- >> net/ipv4/tcp_ipv4.c | 10 +++------- >> net/ipv4/udp.c | 7 +++---- >> 2 files changed, 6 insertions(+), 11 deletions(-) >> >> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c >> index 7766151..4d97b28 100644 >> --- a/net/ipv4/tcp_ipv4.c >> +++ b/net/ipv4/tcp_ipv4.c >> @@ -2214,9 +2214,6 @@ static int tcp_seq_open(struct inode *inode, struct file > *file) >> struct tcp_iter_state *s; >> int err; >> >> - if (unlikely(afinfo == NULL)) >> - return -EINVAL; > I think that this check needs to stay in some form, reason below. >> - >> err = seq_open_net(inode, file, &afinfo->seq_ops, >> sizeof(struct tcp_iter_state)); >> if (err < 0) >> @@ -2241,10 +2238,9 @@ int tcp_proc_register(struct net *net, struct > tcp_seq_afinfo *afinfo) >> afinfo->seq_ops.next = tcp_seq_next; >> afinfo->seq_ops.stop = tcp_seq_stop; >> >> - p = proc_net_fops_create(net, afinfo->name, S_IRUGO, &afinfo->seq_fops); >> - if (p) >> - p->data = afinfo; >> - else >> + p = proc_create_data(afinfo->name, S_IRUGO, net->proc_net, > > When you try to pass in afinfo->name (and also the seq_fops) you are > assuming that afinfo is not null meaning in the unlikely(as shown > above) even that it is null you get a very bad null pointer problem. > If I am just way off do let me know because this just seams to me like > a bad idea. This is also still present in 2.6.26-rc9.
It appears you are getting things confused. The original window is that tcp_seq_open (which is what get called when you open the proc file) had a small race that p->data could be read before it was set.
With proc_create_data that race was closed.
You are saying that it is a problem for tcp_seq_open to be passed a NULL afinfo. It is. That has nothing to do with the original race (as that is a very different part of the code). Feel free to audit all of the callers if you like. That problem however is not subtle or racy.
So I see nothing wrong with this patch unless you can find a problem with proc_create_data.
Eric
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