[PATCH 5.4 305/344] bpf: map_seq_next should always increase position index

Greg Kroah-Hartman
2020-02-21T08:14:28Z

From: Vasily Averin <vvs@virtuozzo.com>

[ Upstream commit 90435a7891a2259b0f74c5a1bc5600d0d64cba8f ]

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: Sasha Levin <sashal@kernel.org>
---
kernel/bpf/inode.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index a70f7209cda3f..218c09ff6a273 100644
--- 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;
}

--
2.20.1