Subject: Re: [PATCH net] ppp: Fix memory leak in ppp_write

From: Guillaume Nault <[email-masked]>
Date: Tue, 24 Sep 2019 17:06:26 +0200

On Sun, Sep 22, 2019 at 04:45:31PM +0900, Takeshi Misawa wrote:
> When ppp is closing, __ppp_xmit_process() failed to enqueue skb
> and skb allocated in ppp_write() is leaked.
> 
> syzbot reported :
> BUG: memory leak
> unreferenced object 0xffff88812a17bc00 (size 224):
>   comm "syz-executor673", pid 6952, jiffies 4294942888 (age 13.040s)
>   hex dump (first 32 bytes):
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace:
>     [<00000000d110fff9>] kmemleak_alloc_recursive include/linux/kmemleak.h:43 [inline]
>     [<00000000d110fff9>] slab_post_alloc_hook mm/slab.h:522 [inline]
>     [<00000000d110fff9>] slab_alloc_node mm/slab.c:3262 [inline]
>     [<00000000d110fff9>] kmem_cache_alloc_node+0x163/0x2f0 mm/slab.c:3574
>     [<000000002d616113>] __alloc_skb+0x6e/0x210 net/core/skbuff.c:197
>     [<000000000167fc45>] alloc_skb include/linux/skbuff.h:1055 [inline]
>     [<000000000167fc45>] ppp_write+0x48/0x120 drivers/net/ppp/ppp_generic.c:502
>     [<000000009ab42c0b>] __vfs_write+0x43/0xa0 fs/read_write.c:494
>     [<00000000086b2e22>] vfs_write fs/read_write.c:558 [inline]
>     [<00000000086b2e22>] vfs_write+0xee/0x210 fs/read_write.c:542
>     [<00000000a2b70ef9>] ksys_write+0x7c/0x130 fs/read_write.c:611
>     [<00000000ce5e0fdd>] __do_sys_write fs/read_write.c:623 [inline]
>     [<00000000ce5e0fdd>] __se_sys_write fs/read_write.c:620 [inline]
>     [<00000000ce5e0fdd>] __x64_sys_write+0x1e/0x30 fs/read_write.c:620
>     [<00000000d9d7b370>] do_syscall_64+0x76/0x1a0 arch/x86/entry/common.c:296
>     [<0000000006e6d506>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Fix this by freeing skb, if ppp is closing.
> 
> Fixes: 6d066734e9f0 ("ppp: avoid loop in xmit recursion detection code")
> Reported-and-tested-by: [email-masked]
> Signed-off-by: Takeshi Misawa <[email-masked]>
> ---
> Dear Guillaume Nault, Paul Mackerras
> 
> syzbot reported memory leak in net/ppp.
> - memory leak in ppp_write
> 
> I send a patch that passed syzbot reproducer test.
> Please consider this memory leak and patch.
> 
> Regards.
> ---
>  drivers/net/ppp/ppp_generic.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
> index a30e41a56085..9a1b006904a7 100644
> --- a/drivers/net/ppp/ppp_generic.c
> +++ b/drivers/net/ppp/ppp_generic.c
> @@ -1415,6 +1415,8 @@ static void __ppp_xmit_process(struct ppp *ppp, struct sk_buff *skb)
>  			netif_wake_queue(ppp->dev);
>  		else
>  			netif_stop_queue(ppp->dev);
> +	} else {
> +		kfree_skb(skb);
>  	}
>  	ppp_xmit_unlock(ppp);
>  }

Thanks a lot Takeshi!

Reviewed-by: Guillaume Nault <[email-masked]>
Tested-by: Guillaume Nault <[email-masked]>