Re: [PATCH 3/3] net: fix iteration for sctp transport seq_files

[Marcelo Ricardo Leitner]

On Fri, Feb 05, 2021 at 11:36:30AM +1100, NeilBrown wrote:
> The sctp transport seq_file iterators take a reference to the transport
> in the ->start and ->next functions and releases the reference in the
> ->show function.  The preferred handling for such resources is to
> release them in the subsequent ->next or ->stop function call.
> 
> Since Commit 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration
> code and interface") there is no guarantee that ->show will be called
> after ->next, so this function can now leak references.
> 
> So move the sctp_transport_put() call to ->next and ->stop.
> 
> Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and 
> interface")
> Reported-by: Xin Long 
> Signed-off-by: NeilBrown 

Acked-by: Marcelo Ricardo Leitner 

[PATCH 3/3] net: fix iteration for sctp transport seq_files

[NeilBrown]

The sctp transport seq_file iterators take a reference to the transport
in the ->start and ->next functions and releases the reference in the
->show function.  The preferred handling for such resources is to
release them in the subsequent ->next or ->stop function call.

Since Commit 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration
code and interface") there is no guarantee that ->show will be called
after ->next, so this function can now leak references.

So move the sctp_transport_put() call to ->next and ->stop.

Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and 
interface")
Reported-by: Xin Long 
Signed-off-by: NeilBrown 
---
 net/sctp/proc.c |   16 
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/net/sctp/proc.c b/net/sctp/proc.c
index f7da88ae20a5..982a87b3e11f 100644
--- a/net/sctp/proc.c
+++ b/net/sctp/proc.c
@@ -215,6 +215,12 @@ static void sctp_transport_seq_stop(struct seq_file *seq, 
void *v)
 {
struct sctp_ht_iter *iter = seq->private;
 
+   if (v && v != SEQ_START_TOKEN) {
+   struct sctp_transport *transport = v;
+
+   sctp_transport_put(transport);
+   }
+
sctp_transport_walk_stop(>hti);
 }
 
@@ -222,6 +228,12 @@ static void *sctp_transport_seq_next(struct seq_file *seq, 
void *v, loff_t *pos)
 {
struct sctp_ht_iter *iter = seq->private;
 
+   if (v && v != SEQ_START_TOKEN) {
+   struct sctp_transport *transport = v;
+
+   sctp_transport_put(transport);
+   }
+
++*pos;
 
return sctp_transport_get_next(seq_file_net(seq), >hti);
@@ -277,8 +289,6 @@ static int sctp_assocs_seq_show(struct seq_file *seq, void 
*v)
sk->sk_rcvbuf);
seq_printf(seq, "\n");
 
-   sctp_transport_put(transport);
-
return 0;
 }
 
@@ -354,8 +364,6 @@ static int sctp_remaddr_seq_show(struct seq_file *seq, void 
*v)
seq_printf(seq, "\n");
}
 
-   sctp_transport_put(transport);
-
return 0;
 }