Re: [netlink] WARNING: at mm/vmalloc.c:1487 __vunmap()

[Eric Dumazet]

On Mon, 2013-06-17 at 22:09 +0200, Pablo Neira Ayuso wrote:

> I've been trying to trigger this bug here with no success using
> different communication configurations (userspace <-> userspace,
> userspace <-> kernelspace).
> 

I got more success with trinity ;)

> The address that vfree shows seems good to me and we always set
> skb->head to NULL after releasing the network buffer.
> 
> This patch also exposes the vmalloc infrastructure to user-space,
> which is something that didn't happen so far. Not sure if Trinity is
> uncovering a bug there.

Nope there are several issues :

1) bug in netlink_alloc_large_skb() because it doesn't account
for sizeof(struct skb_shared_info) overhead and initialization.

2) Also, skb_clone() on such skb should be forbidden.

   Example, nl_fib_input() does a nskb = skb_clone(skb)

If skb is freed before nskb, then nskb wont know skb->head must be freed
by vfree()

I don't know...

3) Do we really need this vmalloc stuff, because it sounds like we are
going to add yet another test in fast path (in skb_free_head())

4) Or we must track all skb_clone() netlink calls to attach a destructor
to properly to the vfree()


[1]
 BUG: unable to handle kernel paging request at ffffc90018a39001
 IP: [<ffffffff814cdeef>] skb_clone+0x1f/0xb0
 PGD c7f40f067 PUD 67f81b067 PMD 65de02067 PTE 0
 Oops: 0000 [#1] [ 1931.190995] scsi_nl_rcv_msg: discarding partial skb
 gsmi: Log Shutdown Reason 0x03
 CPU: 1 PID: 4157 Comm: trinity-child1 Tainted: G        W    3.10.0-smp-DEV #148
 task: ffff880c5fb647f0 ti: ffff880c5ff6c000 task.ti: ffff880c5ff6c000
 RIP: 0010:[<ffffffff814cdeef>]  [<ffffffff814cdeef>] skb_clone+0x1f/0xb0
 RSP: 0018:ffff880c5ff6db18  EFLAGS: 00010282
 RAX: 0000000000002000 RBX: ffff88065fed8ec0 RCX: 0000000060fd8cb3
 RDX: ffffc90018a37000 RSI: 00000000000000d0 RDI: ffff88065fed8ec0
 RBP: ffff880c5ff6db28 R08: ffffc90018a39000 R09: 0000000000000001
 R10: ffffc90018a38fff R11: 0000000000000000 R12: 00000000000000d0
 R13: ffff880c266a0000 R14: ffff88065fed8ec0 R15: 0000000000000000
 FS:  000000000264d880(0063) GS:ffff88067fc20000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: ffffc90018a39001 CR3: 0000000c5b8af000 CR4: 00000000000007e0
 Call Trace:
 [<ffffffff8154b086>] nl_fib_input+0x46/0x140
 [<ffffffff815057ed>] netlink_unicast+0x13d/0x1f0
 [<ffffffff81505b95>] netlink_sendmsg+0x2f5/0x3f0
 [<ffffffff814c366e>] sock_aio_write+0x15e/0x180
 [<ffffffff81193743>] do_sync_readv_writev+0x73/0xb0
 [<ffffffff81194e5b>] do_readv_writev+0xdb/0x2c0



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