crypto: talitos - fix Kernel Oops on hashing an empty file

crypto: talitos - fix Kernel Oops on hashing an empty file

BugLink: http://bugs.launchpad.net/bugs/1751064
commit 87a81dce53b1ea61acaeefa5191a0376a2d1d721 upstream.

Performing the hash of an empty file leads to a kernel Oops

[   44.504600] Unable to handle kernel paging request for data at address 0x0000000c
[   44.512819] Faulting instruction address: 0xc02d2be8
[   44.524088] Oops: Kernel access of bad area, sig: 11 [#1]
[   44.529171] BE PREEMPT CMPC885
[   44.532232] CPU: 0 PID: 491 Comm: md5sum Not tainted 4.15.0-rc8-00211-g3a968610b6ea #81
[   44.540814] NIP:  c02d2be8 LR: c02d2984 CTR: 00000000
[   44.545812] REGS: c6813c90 TRAP: 0300   Not tainted  (4.15.0-rc8-00211-g3a968610b6ea)
[   44.554223] MSR:  00009032 <EE,ME,IR,DR,RI>  CR: 48222822  XER: 20000000
[   44.560855] DAR: 0000000c DSISR: c0000000
[   44.560855] GPR00: c02d28fc c6813d40 c6828000 c646fa40 00000001 00000001 00000001 00000000
[   44.560855] GPR08: 0000004c 00000000 c000bfcc 00000000 28222822 100280d4 00000000 10020008
[   44.560855] GPR16: 00000000 00000020 00000000 00000000 10024008 00000000 c646f9f0 c6179a10
[   44.560855] GPR24: 00000000 00000001 c62f0018 c6179a10 00000000 c6367a30 c62f0000 c646f9c0
[   44.598542] NIP [c02d2be8] ahash_process_req+0x448/0x700
[   44.603751] LR [c02d2984] ahash_process_req+0x1e4/0x700
[   44.608868] Call Trace:
[   44.611329] [c6813d40] [c02d28fc] ahash_process_req+0x15c/0x700 (unreliable)
[   44.618302] [c6813d90] [c02060c4] hash_recvmsg+0x11c/0x210
[   44.623716] [c6813db0] [c0331354] ___sys_recvmsg+0x98/0x138
[   44.629226] [c6813eb0] [c03332c0] __sys_recvmsg+0x40/0x84
[   44.634562] [c6813f10] [c03336c0] SyS_socketcall+0xb8/0x1d4
[   44.640073] [c6813f40] [c000d1ac] ret_from_syscall+0x0/0x38
[   44.645530] Instruction dump:
[   44.648465] 38c00001 7f63db78 4e800421 7c791b78 54690ffe 0f090000 80ff0190 2f870000
[   44.656122] 40befe50 2f990001 409e0210 813f01bc <8129000c> b39e003a 7d29c214 913e003c

This patch fixes that Oops by checking if src is NULL.

Fixes: 6a1e8d14156d4 ("crypto: talitos - making mapping helpers more generic")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>