[PATCH 4.19 16/53] netlink: reset network and mac headers in netlink_dump()

Greg Kroah-Hartman
2022-04-26T08:34:02Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 99c07327ae11e24886d552dddbe4537bfca2765d ]

netlink_dump() is allocating an skb, reserves space in it
but forgets to reset network header.

This allows a BPF program, invoked later from sk_filter()
to access uninitialized kernel memory from the reserved
space.

Theorically mac header reset could be omitted, because
it is set to a special initial value.
bpf_internal_load_pointer_neg_helper calls skb_mac_header()
without checking skb_mac_header_was_set().
Relying on skb->len not being too big seems fragile.
We also could add a sanity check in bpf_internal_load_pointer_neg_helper()
to avoid surprises in the future.

syzbot report was:

BUG: KMSAN: uninit-value in ___bpf_prog_run+0xa22b/0xb420 kernel/bpf/core.c:1637
___bpf_prog_run+0xa22b/0xb420 kernel/bpf/core.c:1637
__bpf_prog_run32+0x121/0x180 kernel/bpf/core.c:1796
bpf_dispatcher_nop_func include/linux/bpf.h:784 [inline]
__bpf_prog_run include/linux/filter.h:626 [inline]
bpf_prog_run include/linux/filter.h:633 [inline]
__bpf_prog_run_save_cb+0x168/0x580 include/linux/filter.h:756
bpf_prog_run_save_cb include/linux/filter.h:770 [inline]
sk_filter_trim_cap+0x3bc/0x8c0 net/core/filter.c:150
sk_filter include/linux/filter.h:905 [inline]
netlink_dump+0xe0c/0x16c0 net/netlink/af_netlink.c:2276
netlink_recvmsg+0x1129/0x1c80 net/netlink/af_netlink.c:2002
sock_recvmsg_nosec net/socket.c:948 [inline]
sock_recvmsg net/socket.c:966 [inline]
sock_read_iter+0x5a9/0x630 net/socket.c:1039
do_iter_readv_writev+0xa7f/0xc70
do_iter_read+0x52c/0x14c0 fs/read_write.c:786
vfs_readv fs/read_write.c:906 [inline]
do_readv+0x432/0x800 fs/read_write.c:943
__do_sys_readv fs/read_write.c:1034 [inline]
__se_sys_readv fs/read_write.c:1031 [inline]
__x64_sys_readv+0xe5/0x120 fs/read_write.c:1031
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x54/0xd0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x44/0xae

Uninit was stored to memory at:
___bpf_prog_run+0x96c/0xb420 kernel/bpf/core.c:1558
__bpf_prog_run32+0x121/0x180 kernel/bpf/core.c:1796
bpf_dispatcher_nop_func include/linux/bpf.h:784 [inline]
__bpf_prog_run include/linux/filter.h:626 [inline]
bpf_prog_run include/linux/filter.h:633 [inline]
__bpf_prog_run_save_cb+0x168/0x580 include/linux/filter.h:756
bpf_prog_run_save_cb include/linux/filter.h:770 [inline]
sk_filter_trim_cap+0x3bc/0x8c0 net/core/filter.c:150
sk_filter include/linux/filter.h:905 [inline]
netlink_dump+0xe0c/0x16c0 net/netlink/af_netlink.c:2276
netlink_recvmsg+0x1129/0x1c80 net/netlink/af_netlink.c:2002
sock_recvmsg_nosec net/socket.c:948 [inline]
sock_recvmsg net/socket.c:966 [inline]
sock_read_iter+0x5a9/0x630 net/socket.c:1039
do_iter_readv_writev+0xa7f/0xc70
do_iter_read+0x52c/0x14c0 fs/read_write.c:786
vfs_readv fs/read_write.c:906 [inline]
do_readv+0x432/0x800 fs/read_write.c:943
__do_sys_readv fs/read_write.c:1034 [inline]
__se_sys_readv fs/read_write.c:1031 [inline]
__x64_sys_readv+0xe5/0x120 fs/read_write.c:1031
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x54/0xd0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x44/0xae

Uninit was created at:
slab_post_alloc_hook mm/slab.h:737 [inline]
slab_alloc_node mm/slub.c:3244 [inline]
__kmalloc_node_track_caller+0xde3/0x14f0 mm/slub.c:4972
kmalloc_reserve net/core/skbuff.c:354 [inline]
__alloc_skb+0x545/0xf90 net/core/skbuff.c:426
alloc_skb include/linux/skbuff.h:1158 [inline]
netlink_dump+0x30f/0x16c0 net/netlink/af_netlink.c:2242
netlink_recvmsg+0x1129/0x1c80 net/netlink/af_netlink.c:2002
sock_recvmsg_nosec net/socket.c:948 [inline]
sock_recvmsg net/socket.c:966 [inline]
sock_read_iter+0x5a9/0x630 net/socket.c:1039
do_iter_readv_writev+0xa7f/0xc70
do_iter_read+0x52c/0x14c0 fs/read_write.c:786
vfs_readv fs/read_write.c:906 [inline]
do_readv+0x432/0x800 fs/read_write.c:943
__do_sys_readv fs/read_write.c:1034 [inline]
__se_sys_readv fs/read_write.c:1031 [inline]
__x64_sys_readv+0xe5/0x120 fs/read_write.c:1031
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x54/0xd0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x44/0xae

CPU: 0 PID: 3470 Comm: syz-executor751 Not tainted 5.17.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Fixes: db65a3aaf29e ("netlink: Trim skb to alloc size to avoid MSG_TRUNC")
Fixes: 9063e21fb026 ("netlink: autosize skb lengthes")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Link: https://lore.kernel.org/r/20220415181442.551228-1-eric.dumazet@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netlink/af_netlink.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 5c6241964637..e2120221b957 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2243,6 +2243,13 @@ static int netlink_dump(struct sock *sk)
* single netdev. The outcome is MSG_TRUNC error.
*/
skb_reserve(skb, skb_tailroom(skb) - alloc_size);
+
+ /* Make sure malicious BPF programs can not read unitialized memory
+ * from skb->head -> skb->data
+ */
+ skb_reset_network_header(skb);
+ skb_reset_mac_header(skb);
+
netlink_skb_set_owner_r(skb, sk);

if (nlk->dump_done_errno > 0)
--
2.35.1