[PATCH net] netfilter: nfnetlink_cthelper: fix OOB read in nfnl_cthelper_dump_table()

[Hyunwoo Kim <imv4bel@gmail.com>]

nfnl_cthelper_dump_table() has a 'goto restart' that jumps to a label
inside the for loop body.  When the "last" helper saved in cb->args[1]
is deleted between dump rounds, every entry fails the (cur != last)
check, so cb->args[1] is never cleared.  The for loop finishes with
cb->args[0] == nf_ct_helper_hsize, and the 'goto restart' jumps back
into the loop body bypassing the bounds check, causing an 8-byte
out-of-bounds read on nf_ct_helper_hash[nf_ct_helper_hsize].

The 'goto restart' block was meant to re-traverse the current bucket
when "last" is no longer found, but it was placed after the for loop
instead of inside it.  Move the block into the for loop body so that
the restart only occurs while cb->args[0] is still within bounds.

KASAN report:

[   42.143286] BUG: KASAN: slab-out-of-bounds in nfnl_cthelper_dump_table+0x9f/0x1b0
[   42.143545] Read of size 8 at addr ffff888104ca3000 by task poc_cthelper/131
[   42.143779]
[   42.143877] CPU: 0 UID: 0 PID: 131 Comm: poc_cthelper Not tainted 7.0.0-rc2+ #6 PREEMPTLAZY
[   42.143884] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[   42.143887] Call Trace:
[   42.143892]  <TASK>
[   42.143893]  dump_stack_lvl+0x64/0x80
[   42.143909]  print_report+0xce/0x660
[   42.143923]  ? __pfx__raw_spin_lock_irqsave+0x10/0x10
[   42.143931]  ? __kmalloc_node_track_caller_noprof+0x2a5/0x590
[   42.143942]  ? __virt_addr_valid+0xef/0x1a0
[   42.143953]  ? nfnl_cthelper_dump_table+0x9f/0x1b0
[   42.143955]  kasan_report+0xce/0x100
[   42.143958]  ? nfnl_cthelper_dump_table+0x9f/0x1b0
[   42.143961]  nfnl_cthelper_dump_table+0x9f/0x1b0
[   42.143964]  netlink_dump+0x333/0x880
[   42.143971]  ? __pfx_netlink_dump+0x10/0x10
[   42.143974]  ? netlink_recvmsg+0x27c/0x4b0
[   42.143976]  ? kmem_cache_free+0x100/0x440
[   42.143978]  ? netlink_recvmsg+0x27c/0x4b0
[   42.143981]  netlink_recvmsg+0x3e2/0x4b0
[   42.143984]  ? aa_sk_perm+0x184/0x450
[   42.143995]  ? __pfx_netlink_recvmsg+0x10/0x10
[   42.143998]  ? __pfx_aa_sk_perm+0x10/0x10
[   42.144000]  ? mutex_unlock+0x80/0xd0
[   42.144003]  ? __pfx_netlink_recvmsg+0x10/0x10
[   42.144005]  sock_recvmsg+0xde/0xf0
[   42.144016]  __sys_recvfrom+0x150/0x200
[   42.144019]  ? __pfx___sys_recvfrom+0x10/0x10
[   42.144022]  ? ksys_write+0xe1/0x160
[   42.144026]  ? __pfx_ksys_write+0x10/0x10
[   42.144028]  __x64_sys_recvfrom+0x76/0x90
[   42.144030]  do_syscall_64+0xc3/0x6e0
[   42.144034]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[   42.144039] RIP: 0033:0x42349d
[   42.144046] Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 80 3d cd 0b 09 00 00 41 89 ca 74 20 45 31 c9 45 31 c0 b8 2d 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 6b c3 66 2e 0f 1f 84 00 00 00 00 00 55 48 89
[   42.144048] RSP: 002b:00007ffc948602e8 EFLAGS: 00000246 ORIG_RAX: 000000000000002d
[   42.144054] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 000000000042349d
[   42.144056] RDX: 0000000000004000 RSI: 00007ffc94860320 RDI: 0000000000000004
[   42.144058] RBP: 00007ffc94864330 R08: 0000000000000000 R09: 0000000000000000
[   42.144059] R10: 0000000000000040 R11: 0000000000000246 R12: 00007ffc94864448
[   42.144060] R13: 00007ffc94864458 R14: 00000000004ae868 R15: 0000000000000001
[   42.144062]  </TASK>
[   42.144063]
[   42.150209] Allocated by task 1:
[   42.150307]  kasan_save_stack+0x33/0x60
[   42.150425]  kasan_save_track+0x14/0x30
[   42.150537]  __kasan_kmalloc+0x8f/0xa0
[   42.150651]  __kvmalloc_node_noprof+0x21b/0x700
[   42.150781]  nf_ct_alloc_hashtable+0x65/0xd0
[   42.150907]  nf_conntrack_helper_init+0x21/0x60
[   42.151040]  nf_conntrack_init_start+0x18d/0x300
[   42.151174]  nf_conntrack_standalone_init+0x12/0xc0
[   42.151327]  do_one_initcall+0xaf/0x320
[   42.151441]  kernel_init_freeable+0x2b6/0x4b0
[   42.151583]  kernel_init+0x1f/0x1e0
[   42.151695]  ret_from_fork+0x205/0x450
[   42.151810]  ret_from_fork_asm+0x1a/0x30
[   42.151927]
[   42.151977] The buggy address belongs to the object at ffff888104ca2000
[   42.151977]  which belongs to the cache kmalloc-4k of size 4096
[   42.152325] The buggy address is located 0 bytes to the right of
[   42.152325]  allocated 4096-byte region [ffff888104ca2000, ffff888104ca3000)
[   42.152697]
[   42.152746] The buggy address belongs to the physical page:
[   42.152908] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x104ca0
[   42.153139] head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
[   42.153356] flags: 0x200000000000040(head|node=0|zone=2)
[   42.153514] page_type: f5(slab)
[   42.153617] raw: 0200000000000040 ffff888100042140 dead000000000122 0000000000000000
[   42.153835] raw: 0000000000000000 0000000800040004 00000000f5000000 0000000000000000
[   42.154052] head: 0200000000000040 ffff888100042140 dead000000000122 0000000000000000
[   42.154272] head: 0000000000000000 0000000800040004 00000000f5000000 0000000000000000
[   42.154498] head: 0200000000000003 ffffea0004132801 00000000ffffffff 00000000ffffffff
[   42.154717] head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
[   42.154933] page dumped because: kasan: bad access detected
[   42.155092]
[   42.155141] Memory state around the buggy address:
[   42.155278]  ffff888104ca2f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   42.155482]  ffff888104ca2f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   42.155684] >ffff888104ca3000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[   42.155886]                    ^
[   42.155981]  ffff888104ca3080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[   42.156183]  ffff888104ca3100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[   42.156385] ==================================================================

Fixes: 12f7a505331e ("netfilter: add user-space connection tracking helper infrastructure")
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
---
 net/netfilter/nfnetlink_cthelper.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/nfnetlink_cthelper.c b/net/netfilter/nfnetlink_cthelper.c
index d658b1478fa0..d545fa459455 100644
--- a/net/netfilter/nfnetlink_cthelper.c
+++ b/net/netfilter/nfnetlink_cthelper.c
@@ -601,10 +601,10 @@ nfnl_cthelper_dump_table(struct sk_buff *skb, struct netlink_callback *cb)
 				goto out;
 			}
 		}
-	}
-	if (cb->args[1]) {
-		cb->args[1] = 0;
-		goto restart;
+		if (cb->args[1]) {
+			cb->args[1] = 0;
+			goto restart;
+		}
 	}
 out:
 	rcu_read_unlock();
-- 
2.43.0