From: David Howells <dhowells@redhat.com>
To: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc: dhowells@redhat.com, Jakub Kicinski <kuba@kernel.org>,
syzbot <syzbot+f527b971b4bdc8e79f9e@syzkaller.appspotmail.com>,
bpf@vger.kernel.org, brauner@kernel.org, davem@davemloft.net,
dsahern@kernel.org, edumazet@google.com,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org, pabeni@redhat.com,
syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk
Subject: Re: Endless loop in udp with MSG_SPLICE_READ - Re: [syzbot] [fs?] INFO: task hung in pipe_release (4)
Date: Tue, 01 Aug 2023 15:01:04 +0100 [thread overview]
Message-ID: <1403253.1690898464@warthog.procyon.org.uk> (raw)
In-Reply-To: <64c903b02b234_1b307829418@willemb.c.googlers.com.notmuch>
Willem de Bruijn <willemdebruijn.kernel@gmail.com> wrote:
> That getfrag is needed. For non-splice cases, to fill the linear part
> of an skb. As your example shows, it is skipped if all data is covered
> by pagedlen?
Yes, because copy goes negative. To quote from the previously quoted log:
==>splice_to_socket() 6630
udp_sendmsg(8,8)
__ip_append_data(copy=-1,len=8, mtu=8192 skblen=8189 maxfl=8188)
pagedlen 9 = 9 - 0
copy -1 = 9 - 0 - 1 - 9
copy is -(the number of excess bytes).
length 8 -= -1 + 0
which then gets deducted from the length - but why? I wonder if copy should
be cleared if we don't call getfrag(). It looks like it's meant to deduct the
amount copied by getfrag(), but that doesn't happen if copy < 0.
Also, note that MSG_ZEROCOPY might see the same maths issue here.
David
next prev parent reply other threads:[~2023-08-01 14:02 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-12 7:35 syzbot
2023-07-12 18:54 ` syzbot
2023-07-18 23:07 ` Jakub Kicinski
2023-07-24 13:17 ` David Howells
2023-07-28 23:52 ` David Howells
2023-07-29 15:27 ` David Howells
2023-07-29 21:49 ` Endless loop in udp with MSG_SPLICE_READ - " David Howells
2023-07-30 13:35 ` Willem de Bruijn
2023-07-30 14:30 ` Willem de Bruijn
2023-07-30 17:32 ` David Howells
2023-07-31 8:13 ` David Howells
2023-07-31 12:45 ` Willem de Bruijn
2023-07-31 13:34 ` David Howells
2023-08-01 12:40 ` David Howells
2023-08-01 12:58 ` Willem de Bruijn
2023-08-01 13:08 ` Willem de Bruijn
2023-08-01 14:01 ` David Howells [this message]
2023-08-01 14:02 ` David Howells
2023-08-01 14:19 ` David Howells
2023-08-01 14:31 ` Willem de Bruijn
2023-08-01 14:47 ` David Howells
2023-08-01 14:59 ` Willem de Bruijn
2023-08-02 13:21 ` David Howells
2023-08-02 16:48 ` syzbot
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