From: Quentin Casasnovas <quentin.casasnovas@xxxxxxxxxx>
Sasha's found a NULL pointer dereference in the RDS connection code when
sending a message to an apparently unbound socket. The problem is caused
by the code checking if the socket is bound in rds_sendmsg(), which checks
the rs_bound_addr field without taking a lock on the socket. This opens a
race where rs_bound_addr is temporarily set but where the transport is not
in rds_bind(), leading to a NULL pointer dereference when trying to
dereference 'trans' in __rds_conn_create().
Vegard wrote a reproducer for this issue, so kindly ask him to share if
you're interested.
I cannot reproduce the NULL pointer dereference using Vegard's reproducer
with this patch, whereas I could without.
Complete earlier incomplete fix to CVE-2015-6937:
74e98eb08588 ("RDS: verify the underlying transport exists before creating a connection")
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Reviewed-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Acked-by: Santosh Shilimkar <santosh.shilimkar@xxxxxxxxxx>
Signed-off-by: Quentin Casasnovas <quentin.casasnovas@xxxxxxxxxx>
---
Dave,
Resending refreshed version from earlier patch which was missed out
for some reason.
https://lkml.org/lkml/2015/10/16/530
It applies cleanly against linus master as well as net-next. I
have also pushed it on my tree below.
git://git.kernel.org/pub/scm/linux/kernel/git/ssantosh/linux.git 4.4/net-next/rds-fix
net/rds/connection.c | 6 ------
net/rds/send.c | 4 +++-
2 files changed, 3 insertions(+), 7 deletions(-)
diff --git a/net/rds/connection.c b/net/rds/connection.c
index d456403..e3b118c 100644
--- a/net/rds/connection.c
+++ b/net/rds/connection.c
@@ -186,12 +186,6 @@ static struct rds_connection *__rds_conn_create(struct net *net,
}
}
- if (trans == NULL) {
- kmem_cache_free(rds_conn_slab, conn);
- conn = ERR_PTR(-ENODEV);
- goto out;
- }
-
conn->c_trans = trans;
ret = trans->conn_alloc(conn, gfp);
diff --git a/net/rds/send.c b/net/rds/send.c
index 827155c..c9cdb35 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -1013,11 +1013,13 @@ int rds_sendmsg(struct socket *sock, struct msghdr *msg, size_t payload_len)
release_sock(sk);
}
- /* racing with another thread binding seems ok here */
+ lock_sock(sk);
if (daddr == 0 || rs->rs_bound_addr == 0) {
+ release_sock(sk);
ret = -ENOTCONN; /* XXX not a great errno */
goto out;
}
+ release_sock(sk);
if (payload_len > rds_sk_sndbuf(rs)) {
ret = -EMSGSIZE;
--
1.9.1
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