tcp: fix UaF in tcp_prune_ofo_queue()

tcp: fix UaF in tcp_prune_ofo_queue()

The CI reported a UaF in tcp_prune_ofo_queue():

BUG: KASAN: slab-use-after-free in tcp_prune_ofo_queue+0x55d/0x660
Read of size 4 at addr ffff8880134729d8 by task socat/20348

CPU: 0 UID: 0 PID: 20348 Comm: socat Not tainted 6.16.0-rc5-virtme #1 PREEMPT(full)
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
Call Trace:
 <TASK>
 dump_stack_lvl+0x82/0xd0
 print_address_description.constprop.0+0x2c/0x400
 print_report+0xb4/0x270
 kasan_report+0xca/0x100
 tcp_prune_ofo_queue+0x55d/0x660
 tcp_try_rmem_schedule+0x855/0x12e0
 tcp_data_queue+0x4dd/0x2260
 tcp_rcv_established+0x5e8/0x2370
 tcp_v4_do_rcv+0x4ba/0x8c0
 __release_sock+0x27a/0x390
 release_sock+0x53/0x1d0
 tcp_sendmsg+0x37/0x50
 sock_write_iter+0x3c1/0x520
 vfs_write+0xc09/0x1210
 ksys_write+0x183/0x1d0
 do_syscall_64+0xc1/0x380
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fcf73ef2337
Code: 0f 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24
RSP: 002b:00007ffd4f924708 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fcf73ef2337
RDX: 0000000000002000 RSI: 0000555f11d1a000 RDI: 0000000000000008
RBP: 0000555f11d1a000 R08: 0000000000002000 R09: 0000000000000000
R10: 0000000000000040 R11: 0000000000000246 R12: 0000000000000008
R13: 0000000000002000 R14: 0000555ee1a44570 R15: 0000000000002000
 </TASK>

Allocated by task 20348:
 kasan_save_stack+0x24/0x50
 kasan_save_track+0x14/0x30
 __kasan_slab_alloc+0x59/0x70
 kmem_cache_alloc_node_noprof+0x110/0x340
 __alloc_skb+0x213/0x2e0
 tcp_collapse+0x43f/0xff0
 tcp_try_rmem_schedule+0x6b9/0x12e0
 tcp_data_queue+0x4dd/0x2260
 tcp_rcv_established+0x5e8/0x2370
 tcp_v4_do_rcv+0x4ba/0x8c0
 __release_sock+0x27a/0x390
 release_sock+0x53/0x1d0
 tcp_sendmsg+0x37/0x50
 sock_write_iter+0x3c1/0x520
 vfs_write+0xc09/0x1210
 ksys_write+0x183/0x1d0
 do_syscall_64+0xc1/0x380
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 20348:
 kasan_save_stack+0x24/0x50
 kasan_save_track+0x14/0x30
 kasan_save_free_info+0x3b/0x60
 __kasan_slab_free+0x38/0x50
 kmem_cache_free+0x149/0x330
 tcp_prune_ofo_queue+0x211/0x660
 tcp_try_rmem_schedule+0x855/0x12e0
 tcp_data_queue+0x4dd/0x2260
 tcp_rcv_established+0x5e8/0x2370
 tcp_v4_do_rcv+0x4ba/0x8c0
 __release_sock+0x27a/0x390
 release_sock+0x53/0x1d0
 tcp_sendmsg+0x37/0x50
 sock_write_iter+0x3c1/0x520
 vfs_write+0xc09/0x1210
 ksys_write+0x183/0x1d0
 do_syscall_64+0xc1/0x380
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888013472900
 which belongs to the cache skbuff_head_cache of size 232
The buggy address is located 216 bytes inside of
 freed 232-byte region [ffff888013472900, ffff8880134729e8)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x13472
head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x80000000000040(head|node=0|zone=1)
page_type: f5(slab)
raw: 0080000000000040 ffff88800198fb40 ffffea0000347b10 ffffea00004f5290
raw: 0000000000000000 0000000000120012 00000000f5000000 0000000000000000
head: 0080000000000040 ffff88800198fb40 ffffea0000347b10 ffffea00004f5290
head: 0000000000000000 0000000000120012 00000000f5000000 0000000000000000
head: 0080000000000001 ffffea00004d1c81 00000000ffffffff 00000000ffffffff
head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888013472880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888013472900: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888013472980: fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc
                                                    ^
 ffff888013472a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888013472a80: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb

Indeed tcp_prune_ofo_queue() is reusing the skb dropped a few lines
above. The caller wants to enqueue 'in_skb', lets check space vs the
latter.

Fixes: 1d2fbaad7cd8 ("tcp: stronger sk_rcvbuf checks")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Tested-by: syzbot+865aca08c0533171bf6a@syzkaller.appspotmail.com
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/b78d2d9bdccca29021eed9a0e7097dd8dc00f485.1752567053.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>