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netlink: reset network and mac headers in netlink_dump() 

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: db65a3aaf2 ("netlink: Trim skb to alloc size to avoid MSG_TRUNC")
Fixes: 9063e21fb0 ("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>
This commit is contained in:
Eric Dumazet 2022-04-15 11:14:42 -07:00 committed by Paolo Abeni
parent 4cf35a2b62
commit 99c07327ae
1 changed files with 7 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
net/netlink/af_netlink.c
View File

@ -2263,6 +2263,13 @@ 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) {