[PATCH 3.10 33/56] netlink: Fix handling of error from netlink_dump().

From: Greg Kroah-Hartman
Date: Sat Jul 26 2014 - 15:59:39 EST

3.10-stable review patch. If anyone has any objections, please let me know.


From: Ben Pfaff <blp@xxxxxxxxxx>

[ Upstream commit ac30ef832e6af0505b6f0251a6659adcfa74975e ]

netlink_dump() returns a negative errno value on error. Until now,
netlink_recvmsg() directly recorded that negative value in sk->sk_err, but
that's wrong since sk_err takes positive errno values. (This manifests as
userspace receiving a positive return value from the recv() system call,
falsely indicating success.) This bug was introduced in the commit that
started checking the netlink_dump() return value, commit b44d211 (netlink:
handle errors from netlink_dump()).

Multithreaded Netlink dumps are one way to trigger this behavior in
practice, as described in the commit message for the userspace workaround
posted here:

This commit also fixes the same bug in netlink_poll(), introduced in commit
cd1df525d (netlink: add flow control for memory mapped I/O).

Signed-off-by: Ben Pfaff <blp@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/netlink/af_netlink.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -500,7 +500,7 @@ static unsigned int netlink_poll(struct
while (nlk->cb != NULL && netlink_dump_space(nlk)) {
err = netlink_dump(sk);
if (err < 0) {
- sk->sk_err = err;
+ sk->sk_err = -err;
@@ -2272,7 +2272,7 @@ static int netlink_recvmsg(struct kiocb
if (nlk->cb && atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf / 2) {
ret = netlink_dump(sk);
if (ret) {
- sk->sk_err = ret;
+ sk->sk_err = -ret;

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