bpf: map_seq_next should always increase position index

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 <[email protected]> Signed-off-by: Daniel Borkmann <[email protected]> Link: https://lore.kernel.org/bpf/[email protected]
ambv · Jan 27, 2020 · 90435a7 · 90435a7
1 parent 07fdbee
commit 90435a7
Showing 1 changed file with 1 addition and 2 deletions.
diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
@@ -196,6 +196,7 @@ 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;
 
@@ -208,8 +209,6 @@ static void *map_seq_next(struct seq_file *m, void *v, loff_t *pos)
 		map_iter(m)->done = true;
 		return NULL;
 	}
-
-	++(*pos);
 	return key;
 }