6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kees Cook keescook@chromium.org
[ Upstream commit b5f0de6df6dce8d641ef58ef7012f3304dffb9a1 ]
One of the worst offenders of "fake flexible arrays" is struct sockaddr, as it is the classic example of why GCC and Clang have been traditionally forced to treat all trailing arrays as fake flexible arrays: in the distant misty past, sa_data became too small, and code started just treating it as a flexible array, even though it was fixed-size. The special case by the compiler is specifically that sizeof(sa->sa_data) and FORTIFY_SOURCE (which uses __builtin_object_size(sa->sa_data, 1)) do not agree (14 and -1 respectively), which makes FORTIFY_SOURCE treat it as a flexible array.
However, the coming -fstrict-flex-arrays compiler flag will remove these special cases so that FORTIFY_SOURCE can gain coverage over all the trailing arrays in the kernel that are _not_ supposed to be treated as a flexible array. To deal with this change, convert sa_data to a true flexible array. To keep the structure size the same, move sa_data into a union with a newly introduced sa_data_min with the original size. The result is that FORTIFY_SOURCE can continue to have no idea how large sa_data may actually be, but anything using sizeof(sa->sa_data) must switch to sizeof(sa->sa_data_min).
Cc: Jens Axboe axboe@kernel.dk Cc: Pavel Begunkov asml.silence@gmail.com Cc: David Ahern dsahern@kernel.org Cc: Dylan Yudaken dylany@fb.com Cc: Yajun Deng yajun.deng@linux.dev Cc: Petr Machata petrm@nvidia.com Cc: Hangbin Liu liuhangbin@gmail.com Cc: Leon Romanovsky leon@kernel.org Cc: syzbot syzkaller@googlegroups.com Cc: Willem de Bruijn willemb@google.com Cc: Pablo Neira Ayuso pablo@netfilter.org Signed-off-by: Kees Cook keescook@chromium.org Link: https://lore.kernel.org/r/20221018095503.never.671-kees@kernel.org Signed-off-by: Jakub Kicinski kuba@kernel.org Stable-dep-of: a7d6027790ac ("arp: Prevent overflow in arp_req_get().") Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/socket.h | 5 ++++- net/core/dev.c | 2 +- net/core/dev_ioctl.c | 2 +- net/packet/af_packet.c | 10 +++++----- 4 files changed, 11 insertions(+), 8 deletions(-)
diff --git a/include/linux/socket.h b/include/linux/socket.h index b3c58042bd254..d79efd0268809 100644 --- a/include/linux/socket.h +++ b/include/linux/socket.h @@ -33,7 +33,10 @@ typedef __kernel_sa_family_t sa_family_t;
struct sockaddr { sa_family_t sa_family; /* address family, AF_xxx */ - char sa_data[14]; /* 14 bytes of protocol address */ + union { + char sa_data_min[14]; /* Minimum 14 bytes of protocol address */ + DECLARE_FLEX_ARRAY(char, sa_data); + }; };
struct linger { diff --git a/net/core/dev.c b/net/core/dev.c index 1ba3662faf0aa..60619fe8af5fc 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -8861,7 +8861,7 @@ EXPORT_SYMBOL(dev_set_mac_address_user);
int dev_get_mac_address(struct sockaddr *sa, struct net *net, char *dev_name) { - size_t size = sizeof(sa->sa_data); + size_t size = sizeof(sa->sa_data_min); struct net_device *dev; int ret = 0;
diff --git a/net/core/dev_ioctl.c b/net/core/dev_ioctl.c index 7674bb9f3076c..5cdbfbf9a7dcf 100644 --- a/net/core/dev_ioctl.c +++ b/net/core/dev_ioctl.c @@ -342,7 +342,7 @@ static int dev_ifsioc(struct net *net, struct ifreq *ifr, void __user *data, if (ifr->ifr_hwaddr.sa_family != dev->type) return -EINVAL; memcpy(dev->broadcast, ifr->ifr_hwaddr.sa_data, - min(sizeof(ifr->ifr_hwaddr.sa_data), + min(sizeof(ifr->ifr_hwaddr.sa_data_min), (size_t)dev->addr_len)); call_netdevice_notifiers(NETDEV_CHANGEADDR, dev); return 0; diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 51882f07ef70c..c3117350f5fbb 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -3284,7 +3284,7 @@ static int packet_bind_spkt(struct socket *sock, struct sockaddr *uaddr, int addr_len) { struct sock *sk = sock->sk; - char name[sizeof(uaddr->sa_data) + 1]; + char name[sizeof(uaddr->sa_data_min) + 1];
/* * Check legality @@ -3295,8 +3295,8 @@ static int packet_bind_spkt(struct socket *sock, struct sockaddr *uaddr, /* uaddr->sa_data comes from the userspace, it's not guaranteed to be * zero-terminated. */ - memcpy(name, uaddr->sa_data, sizeof(uaddr->sa_data)); - name[sizeof(uaddr->sa_data)] = 0; + memcpy(name, uaddr->sa_data, sizeof(uaddr->sa_data_min)); + name[sizeof(uaddr->sa_data_min)] = 0;
return packet_do_bind(sk, name, 0, 0); } @@ -3566,11 +3566,11 @@ static int packet_getname_spkt(struct socket *sock, struct sockaddr *uaddr, return -EOPNOTSUPP;
uaddr->sa_family = AF_PACKET; - memset(uaddr->sa_data, 0, sizeof(uaddr->sa_data)); + memset(uaddr->sa_data, 0, sizeof(uaddr->sa_data_min)); rcu_read_lock(); dev = dev_get_by_index_rcu(sock_net(sk), READ_ONCE(pkt_sk(sk)->ifindex)); if (dev) - strscpy(uaddr->sa_data, dev->name, sizeof(uaddr->sa_data)); + strscpy(uaddr->sa_data, dev->name, sizeof(uaddr->sa_data_min)); rcu_read_unlock();
return sizeof(*uaddr);