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Message-ID: <82046b6cf70823e8c17e102c8233f1cb219bb9f5.camel@redhat.com>
Date: Tue, 20 Feb 2024 13:06:18 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>, "David S. Miller"
<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
<kuba@...nel.org>
Cc: Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v1 net-next 03/16] af_unix: Link struct unix_edge when
queuing skb.
On Fri, 2024-02-02 at 19:00 -0800, Kuniyuki Iwashima wrote:
> Just before queuing skb with inflight fds, we call scm_stat_add(),
> which is a good place to set up the preallocated struct unix_edge
> in UNIXCB(skb).fp->edges.
>
> Then, we call unix_add_edges() and construct the directed graph
> as follows:
>
> 1. Set the inflight socket's unix_vertex to unix_edge.predecessor
> 2. Set the receiver's unix_vertex to unix_edge.successor
> 3. Link unix_edge.entry to the inflight socket's unix_vertex.edges
> 4. Link inflight socket's unix_vertex.entry to unix_unvisited_vertices.
>
> Let's say we pass the fd of AF_UNIX socket A to B and the fd of B
> to C. The graph looks like this:
>
> +-------------------------+
> | unix_unvisited_vertices | <------------------------.
> +-------------------------+ |
> + |
> | +-------------+ +-------------+ | +-------------+
> | | unix_sock A | | unix_sock B | | | unix_sock C |
> | +-------------+ +-------------+ | +-------------+
> | | unix_vertex | <----. .----> | unix_vertex | <-|--. .----> | unix_vertex |
> | | +-----------+ | | | +-----------+ | | | | +-----------+
> `-> | | entry | +------------> | | entry | +-' | | | | entry |
> | |-----------| | | | |-----------| | | | |-----------|
> | | edges | <-. | | | | edges | <-. | | | | edges |
> +-+-----------+ | | | +-+-----------+ | | | +-+-----------+
> | | | | | |
> .---------------------' | | .---------------------' | |
> | | | | | |
> | +-------------+ | | | +-------------+ | |
> | | unix_edge | | | | | unix_edge | | |
> | +-------------+ | | | +-------------+ | |
> `-> | entry | | | `-> | entry | | |
> |-------------| | | |-------------| | |
> | predecessor | +----' | | predecessor | +----' |
> |-------------| | |-------------| |
> | successor | +-------' | successor | +-------'
> +-------------+ +-------------+
>
> Henceforth, we denote such a graph as A -> B (-> C).
>
> Now, we can express all inflight fd graphs that do not contain
> embryo sockets. The following two patches will support the
> particular case.
>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> ---
> include/net/af_unix.h | 2 ++
> include/net/scm.h | 1 +
> net/core/scm.c | 2 ++
> net/unix/af_unix.c | 8 +++++--
> net/unix/garbage.c | 56 ++++++++++++++++++++++++++++++++++++++++++-
> 5 files changed, 66 insertions(+), 3 deletions(-)
>
> diff --git a/include/net/af_unix.h b/include/net/af_unix.h
> index cab9dfb666f3..54d62467a70b 100644
> --- a/include/net/af_unix.h
> +++ b/include/net/af_unix.h
> @@ -23,6 +23,8 @@ extern unsigned int unix_tot_inflight;
> void unix_inflight(struct user_struct *user, struct file *fp);
> void unix_notinflight(struct user_struct *user, struct file *fp);
> void unix_init_vertex(struct unix_sock *u);
> +void unix_add_edges(struct scm_fp_list *fpl, struct unix_sock *receiver);
> +void unix_del_edges(struct scm_fp_list *fpl);
> int unix_alloc_edges(struct scm_fp_list *fpl);
> void unix_free_edges(struct scm_fp_list *fpl);
> void unix_gc(void);
> diff --git a/include/net/scm.h b/include/net/scm.h
> index a1142dee086c..7d807fe466a3 100644
> --- a/include/net/scm.h
> +++ b/include/net/scm.h
> @@ -32,6 +32,7 @@ struct scm_fp_list {
> short count_unix;
> short max;
> #ifdef CONFIG_UNIX
> + bool inflight;
> struct unix_edge *edges;
> #endif
> struct user_struct *user;
> diff --git a/net/core/scm.c b/net/core/scm.c
> index 8661524ed6e5..d141c00eb116 100644
> --- a/net/core/scm.c
> +++ b/net/core/scm.c
> @@ -87,6 +87,7 @@ static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
> *fplp = fpl;
> fpl->count = 0;
> fpl->count_unix = 0;
> + fpl->inflight = false;
> fpl->edges = NULL;
> fpl->max = SCM_MAX_FD;
> fpl->user = NULL;
> @@ -378,6 +379,7 @@ struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
> for (i = 0; i < fpl->count; i++)
> get_file(fpl->fp[i]);
>
> + new_fpl->inflight = false;
> new_fpl->edges = NULL;
> new_fpl->max = new_fpl->count;
> new_fpl->user = get_uid(fpl->user);
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 0391f66546a6..ea7bac18a781 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -1956,8 +1956,10 @@ static void scm_stat_add(struct sock *sk, struct sk_buff *skb)
> struct scm_fp_list *fp = UNIXCB(skb).fp;
> struct unix_sock *u = unix_sk(sk);
>
> - if (unlikely(fp && fp->count))
> + if (unlikely(fp && fp->count)) {
> atomic_add(fp->count, &u->scm_stat.nr_fds);
> + unix_add_edges(fp, u);
> + }
> }
>
> static void scm_stat_del(struct sock *sk, struct sk_buff *skb)
> @@ -1965,8 +1967,10 @@ static void scm_stat_del(struct sock *sk, struct sk_buff *skb)
> struct scm_fp_list *fp = UNIXCB(skb).fp;
> struct unix_sock *u = unix_sk(sk);
>
> - if (unlikely(fp && fp->count))
> + if (unlikely(fp && fp->count)) {
> atomic_sub(fp->count, &u->scm_stat.nr_fds);
> + unix_del_edges(fp);
> + }
> }
>
> /*
> diff --git a/net/unix/garbage.c b/net/unix/garbage.c
> index 6a3572e43b9f..572ac0994c69 100644
> --- a/net/unix/garbage.c
> +++ b/net/unix/garbage.c
> @@ -110,6 +110,58 @@ void unix_init_vertex(struct unix_sock *u)
> INIT_LIST_HEAD(&vertex->entry);
> }
>
> +DEFINE_SPINLOCK(unix_gc_lock);
> +static LIST_HEAD(unix_unvisited_vertices);
> +
> +void unix_add_edges(struct scm_fp_list *fpl, struct unix_sock *receiver)
> +{
> + int i = 0, j = 0;
> +
> + spin_lock(&unix_gc_lock);
> +
> + while (i < fpl->count_unix) {
> + struct unix_sock *inflight = unix_get_socket(fpl->fp[j++]);
> + struct unix_edge *edge;
> +
> + if (!inflight)
> + continue;
> +
> + edge = fpl->edges + i++;
> + edge->predecessor = &inflight->vertex;
> + edge->successor = &receiver->vertex;
> +
> + if (!edge->predecessor->out_degree++)
> + list_add_tail(&edge->predecessor->entry, &unix_unvisited_vertices);
> +
> + INIT_LIST_HEAD(&edge->entry);
Here 'edge->predecessor->entry' and 'edge->entry' refer to different
object types right ? edge vs vertices. Perhaps using different field
names could clarify the code a bit?
Also the edge->entry initialization just before the list_add_tail below
looks strange/suspect. Perhaps it would be better to the init at
allocation time?
Thanks!
Paolo
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