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Date
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SubjectRe: memory corruption in tcp bind hash buckets on SMP?

1st patch: reverses the insertion order in __tcp_tw_hashdance(). This is what
we tested

2nd patch: removes conditional around tw->tb in tcp_timewait_kill(). I have
only made sure it compiles. "tw-tb == NULL;" is not strictly required.. but
esures oops if we end up in similar race again.

patch 1:
--------

--- linux-2.4.7-10/net/ipv4/tcp_minisocks.c Thu Sep 6 13:11:49 2001
+++ linux-2.4.7-10-mod/net/ipv4/tcp_minisocks.c Fri Mar 1 15:41:26 2002
@@ -304,9 +304,25 @@
struct tcp_bind_hashbucket *bhead;
struct sock **head, *sktw;

+
+ /* Step 1: Put TW into bind hash. Original socket stays there too.
+ Note, that any socket with sk->num!=0 MUST be bound in binding
+ cache, even if it is closed.
+ */
+ bhead = &tcp_bhash[tcp_bhashfn(sk->num)];
+ spin_lock(&bhead->lock);
+ tw->tb = (struct tcp_bind_bucket *)sk->prev;
+ BUG_TRAP(sk->prev!=NULL);
+ if ((tw->bind_next = tw->tb->owners) != NULL)
+ tw->tb->owners->bind_pprev = &tw->bind_next;
+ tw->tb->owners = (struct sock*)tw;
+ tw->bind_pprev = &tw->tb->owners;
+ spin_unlock(&bhead->lock);
+
write_lock(&ehead->lock);

- /* Step 1: Remove SK from established hash. */
+ /* Step 2: Remove SK from established hash. */
if (sk->pprev) {
if(sk->next)
sk->next->pprev = sk->pprev;
@@ -315,7 +331,7 @@
sock_prot_dec_use(sk->prot);
}

- /* Step 2: Hash TW into TIMEWAIT half of established hash table. */
+ /* Step 3: Hash TW into TIMEWAIT half of established hash table. */
head = &(ehead + tcp_ehash_size)->chain;
sktw = (struct sock *)tw;
if((sktw->next = *head) != NULL)
@@ -325,20 +341,6 @@
atomic_inc(&tw->refcnt);

write_unlock(&ehead->lock);
-
- /* Step 3: Put TW into bind hash. Original socket stays there too.
- Note, that any socket with sk->num!=0 MUST be bound in binding
- cache, even if it is closed.
- */
- bhead = &tcp_bhash[tcp_bhashfn(sk->num)];
- spin_lock(&bhead->lock);
- tw->tb = (struct tcp_bind_bucket *)sk->prev;
- BUG_TRAP(sk->prev!=NULL);
- if ((tw->bind_next = tw->tb->owners) != NULL)
- tw->tb->owners->bind_pprev = &tw->bind_next;
- tw->tb->owners = (struct sock*)tw;
- tw->bind_pprev = &tw->tb->owners;
- spin_unlock(&bhead->lock);
}

/*

patch 2:
--------
--- linux-2.4.7-10/net/ipv4/tcp_minisocks.c Thu Sep 6 13:11:49 2001
+++ linux-2.4.7-10-mod/net/ipv4/tcp_minisocks.c Mon Mar 4 16:41:35 2002
@@ -75,17 +75,16 @@
/* Disassociate with bind bucket. */
bhead = &tcp_bhash[tcp_bhashfn(tw->num)];
spin_lock(&bhead->lock);
- if ((tb = tw->tb) != NULL) {
- if(tw->bind_next)
- tw->bind_next->bind_pprev = tw->bind_pprev;
- *(tw->bind_pprev) = tw->bind_next;
- tw->tb = NULL;
- if (tb->owners == NULL) {
- if (tb->next)
- tb->next->pprev = tb->pprev;
- *(tb->pprev) = tb->next;
- kmem_cache_free(tcp_bucket_cachep, tb);
- }
+ tb = tw->tb;
+ if(tw->bind_next)
+ tw->bind_next->bind_pprev = tw->bind_pprev;
+ *(tw->bind_pprev) = tw->bind_next;
+ tw->tb = NULL;
+ if (tb->owners == NULL) {
+ if (tb->next)
+ tb->next->pprev = tb->pprev;
+ *(tb->pprev) = tb->next;
+ kmem_cache_free(tcp_bucket_cachep, tb);
}
spin_unlock(&bhead->lock);

--- "David S. Miller" <davem@redhat.com> wrote:
> From: Raghu Angadi <raghuangadi@yahoo.com>
> Date: Mon, 4 Mar 2002 12:48:32 -0800 (PST)
> We have been load testing the kernel with this patch (reverse the
> insertion
> order in __tcp_tw_hashdance(). It seems to work fine till now.
>
> Where was "this patch" posted? I never saw anyone post
> any code, all anyone did was merely describe the change :)


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