release/5.2.40/bpf-map_seq_next-should-always-increase-position-ind.patch

From e9eeeb4ebea8ec9c50dd0a1682619b60cd4b71a4 Mon Sep 17 00:00:00 2001
From: Vasily Averin <vvs@virtuozzo.com>
Date: Sat, 25 Jan 2020 12:10:02 +0300
Subject: [PATCH] bpf: map_seq_next should always increase position index

commit 90435a7891a2259b0f74c5a1bc5600d0d64cba8f upstream.

If seq_file .next fuction does not change position index,
read after some lseek can generate an unexpected output.

See also: https://bugzilla.kernel.org/show_bug.cgi?id=206283

v1 -> v2: removed missed increment in end of function

Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/eca84fdd-c374-a154-d874-6c7b55fc3bc4@virtuozzo.com
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index cc0d0cf114e3..482e259ffcfb 100644
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -195,6 +195,7 @@ static void *map_seq_next(struct seq_file *m, void *v, loff_t *pos)
 	void *key = map_iter(m)->key;
 	void *prev_key;
 
+	(*pos)++;
 	if (map_iter(m)->done)
 		return NULL;
 
@@ -207,8 +208,6 @@ static void *map_seq_next(struct seq_file *m, void *v, loff_t *pos)
 		map_iter(m)->done = true;
 		return NULL;
 	}
-
-	++(*pos);
 	return key;
 }
 
-- 
2.7.4