Fixed function sk_msg_clone() to prevent overflow of 'dst' while adding
pages in scatterlist entries. The overflow of 'dst' causes crash in kernel
tls module while doing record encryption.

Crash fixed by this patch.

[   78.796119] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008
[   78.804900] Mem abort info:
[   78.807683]   ESR = 0x96000004
[   78.810744]   Exception class = DABT (current EL), IL = 32 bits
[   78.816677]   SET = 0, FnV = 0
[   78.819727]   EA = 0, S1PTW = 0
[   78.822873] Data abort info:
[   78.825759]   ISV = 0, ISS = 0x00000004
[   78.829600]   CM = 0, WnR = 0
[   78.832576] user pgtable: 4k pages, 48-bit VAs, pgdp = 00000000bf8ee311
[   78.839195] [0000000000000008] pgd=0000000000000000
[   78.844081] Internal error: Oops: 96000004 [#1] PREEMPT SMP
[   78.849642] Modules linked in: tls xt_conntrack ipt_REJECT nf_reject_ipv4 ip6table_filter ip6_tables xt_CHECKSUM cpve cpufreq_conservative lm90 ina2xx crct10dif_ce
[   78.865377] CPU: 0 PID: 6007 Comm: openssl Not tainted 4.20.0-rc6-01647-g754d5da6-dirty #107
[   78.874149] Hardware name: LS1043A RDB Board (DT)
[   78.878844] pstate: 60000005 (nZCv daif -PAN -UAO)
[   78.883632] pc : scatterwalk_copychunks+0x164/0x1c8
[   78.888500] lr : scatterwalk_copychunks+0x160/0x1c8
[   78.893366] sp : ffff00001d04b600
[   78.896668] x29: ffff00001d04b600 x28: ffff80006814c680
[   78.901970] x27: 0000000000000000 x26: ffff80006c8de786
[   78.907272] x25: ffff00001d04b760 x24: 000000000000001a
[   78.912573] x23: 0000000000000006 x22: ffff80006814e440
[   78.917874] x21: 0000000000000100 x20: 0000000000000000
[   78.923175] x19: 000081ffffffffff x18: 0000000000000400
[   78.928476] x17: 0000000000000008 x16: 0000000000000000
[   78.933778] x15: 0000000000000100 x14: 0000000000000001
[   78.939079] x13: 0000000000001080 x12: 0000000000000020
[   78.944381] x11: 0000000000001080 x10: 00000000ffff0002
[   78.949683] x9 : ffff80006814c248 x8 : 00000000ffff0000
[   78.954985] x7 : ffff80006814c318 x6 : ffff80006c8de786
[   78.960286] x5 : 0000000000000f80 x4 : ffff80006c8de000
[   78.965588] x3 : 0000000000000000 x2 : 0000000000001086
[   78.970889] x1 : ffff7e0001b74e02 x0 : 0000000000000000
[   78.976192] Process openssl (pid: 6007, stack limit = 0x00000000291367f9)
[   78.982968] Call trace:
[   78.985406]  scatterwalk_copychunks+0x164/0x1c8
[   78.989927]  skcipher_walk_next+0x28c/0x448
[   78.994099]  skcipher_walk_done+0xfc/0x258
[   78.998187]  gcm_encrypt+0x434/0x4c0
[   79.001758]  tls_push_record+0x354/0xa58 [tls]
[   79.006194]  bpf_exec_tx_verdict+0x1e4/0x3e8 [tls]
[   79.010978]  tls_sw_sendmsg+0x650/0x780 [tls]
[   79.015326]  inet_sendmsg+0x2c/0xf8
[   79.018806]  sock_sendmsg+0x18/0x30
[   79.022284]  __sys_sendto+0x104/0x138
[   79.025935]  __arm64_sys_sendto+0x24/0x30
[   79.029936]  el0_svc_common+0x60/0xe8
[   79.033588]  el0_svc_handler+0x2c/0x80
[   79.037327]  el0_svc+0x8/0xc
[   79.040200] Code: 6b01005f 54fff788 940169b1 f9000320 (b9400801)
[   79.046283] ---[ end trace 74db007d069c1cf7 ]---

Fixes: d829e9c4

 ("tls: convert to generic sk_msg interface")
Signed-off-by: Vakul Garg <vakul.garg@nxp.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>