[PATCH 1/2] taskstats: return -EBADF when cgroupstats receives an invalid fd

[Yiyang Chen]

cgroupstats_user_cmd() returns 0 without sending a reply or a netlink
error when the fd passed via CGROUPSTATS_CMD_ATTR_FD does not resolve
to an open file in the caller's table.  As a result:

- clients that did not set NLM_F_ACK block on recv() indefinitely
waiting for a CGROUPSTATS_CMD_NEW message that is never emitted;
- clients that set NLM_F_ACK receive a misleading "success" ACK
(errno == 0) with no statistics payload.

Return -EBADF instead so the netlink layer propagates the error to
userspace as expected.

Signed-off-by: Yiyang Chen <cyyzero16@xxxxxxxxx>
---
 kernel/taskstats.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index 2cd0172d0516..8d115670a3ca 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -423,7 +423,7 @@ static int cgroupstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
 	fd = nla_get_u32(info->attrs[CGROUPSTATS_CMD_ATTR_FD]);
 	CLASS(fd, f)(fd);
 	if (fd_empty(f))
-		return 0;
+		return -EBADF;
 
 	size = nla_total_size(sizeof(struct cgroupstats));
 
-- 
2.43.0