dccp: Fix memory leak in dccp_feat_change_recv

If dccp_feat_push_confirm() fails after new value for SP feature was accepted
without reconciliation ('entry == NULL' branch), memory allocated for that value
with dccp_feat_clone_sp_val() is never freed.

Here is the kmemleak stack for this:

unreferenced object 0xffff88801d4ab488 (size 8):
  comm "syz-executor310", pid 1127, jiffies 4295085598 (age 41.666s)
  hex dump (first 8 bytes):
    01 b4 4a 1d 80 88 ff ff                          ..J.....
  backtrace:
    [<00000000db7cabfe>] kmemdup+0x23/0x50 mm/util.c:128
    [<0000000019b38405>] kmemdup include/linux/string.h:465 [inline]
    [<0000000019b38405>] dccp_feat_clone_sp_val net/dccp/feat.c:371 [inline]
    [<0000000019b38405>] dccp_feat_clone_sp_val net/dccp/feat.c:367 [inline]
    [<0000000019b38405>] dccp_feat_change_recv net/dccp/feat.c:1145 [inline]
    [<0000000019b38405>] dccp_feat_parse_options+0x1196/0x2180 net/dccp/feat.c:1416
    [<00000000b1f6d94a>] dccp_parse_options+0xa2a/0x1260 net/dccp/options.c:125
    [<0000000030d7b621>] dccp_rcv_state_process+0x197/0x13d0 net/dccp/input.c:650
    [<000000001f74c72e>] dccp_v4_do_rcv+0xf9/0x1a0 net/dccp/ipv4.c:688
    [<00000000a6c24128>] sk_backlog_rcv include/net/sock.h:1041 [inline]
    [<00000000a6c24128>] __release_sock+0x139/0x3b0 net/core/sock.c:2570
    [<00000000cf1f3a53>] release_sock+0x54/0x1b0 net/core/sock.c:3111
    [<000000008422fa23>] inet_wait_for_connect net/ipv4/af_inet.c:603 [inline]
    [<000000008422fa23>] __inet_stream_connect+0x5d0/0xf70 net/ipv4/af_inet.c:696
    [<0000000015b6f64d>] inet_stream_connect+0x53/0xa0 net/ipv4/af_inet.c:735
    [<0000000010122488>] __sys_connect_file+0x15c/0x1a0 net/socket.c:1865
    [<00000000b4b70023>] __sys_connect+0x165/0x1a0 net/socket.c:1882
    [<00000000f4cb3815>] __do_sys_connect net/socket.c:1892 [inline]
    [<00000000f4cb3815>] __se_sys_connect net/socket.c:1889 [inline]
    [<00000000f4cb3815>] __x64_sys_connect+0x6e/0xb0 net/socket.c:1889
    [<00000000e7b1e839>] do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46
    [<0000000055e91434>] entry_SYSCALL_64_after_hwframe+0x67/0xd1

Clean up the allocated memory in case of dccp_feat_push_confirm() failure
and bail out with an error reset code.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: e77b836 ("dccp: Process incoming Change feature-negotiation options")
Signed-off-by: Ivan Solodovnikov <solodovnikov.ia@phystech.edu>
Link: https://patch.msgid.link/20241126143902.190853-1-solodovnikov.ia@phystech.edu
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: Ivan Solodovnikov

net/dccp/feat.c

@@ -1166,8 +1166,12 @@ static u8 dccp_feat_change_recv(struct list_head *fn, u8 is_mandatory, u8 opt,
 			goto not_valid_or_not_known;
 		}
 
-		return dccp_feat_push_confirm(fn, feat, local, &fval);
+		if (dccp_feat_push_confirm(fn, feat, local, &fval)) {
+			kfree(fval.sp.vec);
+			return DCCP_RESET_CODE_TOO_BUSY;
+		}
 
+		return 0;
 	} else if (entry->state == FEAT_UNSTABLE) {	/* 6.6.2 */
 		return 0;
 	}