crypto: caam - fix use-after-free KASAN issue for RSA algorithms

Here's the KASAN report:
BUG: KASAN: use-after-free in rsa_pub_done+0x70/0xe8
Read of size 1 at addr ffff000023082014 by task swapper/0/0

CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.6.0-rc1-00162-gfcb90d51 #60
Hardware name: LS1046A RDB Board (DT)
Call trace:
 dump_backtrace+0x0/0x260
 show_stack+0x14/0x20
 dump_stack+0xe8/0x144
 print_address_description.isra.11+0x64/0x348
 __kasan_report+0x11c/0x230
 kasan_report+0xc/0x18
 __asan_load1+0x5c/0x68
 rsa_pub_done+0x70/0xe8
 caam_jr_dequeue+0x390/0x608
 tasklet_action_common.isra.13+0x1ec/0x230
 tasklet_action+0x24/0x30
 efi_header_end+0x1a4/0x370
 irq_exit+0x114/0x128
 __handle_domain_irq+0x80/0xe0
 gic_handle_irq+0x50/0xa0
 el1_irq+0xb8/0x180
 cpuidle_enter_state+0xa4/0x490
 cpuidle_enter+0x48/0x70
 call_cpuidle+0x44/0x70
 do_idle+0x304/0x338
 cpu_startup_entry+0x24/0x40
 rest_init+0xf8/0x10c
 arch_call_rest_init+0xc/0x14
 start_kernel+0x774/0x7b4

Allocated by task 263:
 save_stack+0x24/0xb0
 __kasan_kmalloc.isra.10+0xc4/0xe0
 kasan_kmalloc+0xc/0x18
 __kmalloc+0x178/0x2b8
 rsa_edesc_alloc+0x2cc/0xe10
 caam_rsa_enc+0x9c/0x5f0
 test_akcipher_one+0x78c/0x968
 alg_test_akcipher+0x78/0xf8
 alg_test.part.44+0x114/0x4a0
 alg_test+0x1c/0x60
 cryptomgr_test+0x34/0x58
 kthread+0x1b8/0x1c0
 ret_from_fork+0x10/0x18

Freed by task 0:
 save_stack+0x24/0xb0
 __kasan_slab_free+0x10c/0x188
 kasan_slab_free+0x10/0x18
 kfree+0x7c/0x298
 rsa_pub_done+0x68/0xe8
 caam_jr_dequeue+0x390/0x608
 tasklet_action_common.isra.13+0x1ec/0x230
 tasklet_action+0x24/0x30
 efi_header_end+0x1a4/0x370

The buggy address belongs to the object at ffff000023082000
 which belongs to the cache dma-kmalloc-256 of size 256
The buggy address is located 20 bytes inside of
 256-byte region [ffff000023082000, ffff000023082100)
The buggy address belongs to the page:
page:fffffe00006c2080 refcount:1 mapcount:0 mapping:ffff00093200c200 index:0x0 compound_mapcount: 0
flags: 0xffff00000010200(slab|head)
raw: 0ffff00000010200 dead000000000100 dead000000000122 ffff00093200c200
raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff000023081f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff000023081f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff000023082000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                         ^
 ffff000023082080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff000023082100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

Fixes: bf537950 ("crypto: caam - add crypto_engine support for RSA algorithms")
Signed-off-by: Iuliana Prodan <iuliana.prodan@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/caam/caampkc.c

@@ -121,11 +121,13 @@ static void rsa_pub_done(struct device *dev, u32 *desc, u32 err, void *context)
 	struct caam_drv_private_jr *jrp = dev_get_drvdata(dev);
 	struct rsa_edesc *edesc;
 	int ecode = 0;
+	bool has_bklog;
 
 	if (err)
 		ecode = caam_jr_strstatus(dev, err);
 
 	edesc = req_ctx->edesc;
+	has_bklog = edesc->bklog;
 
 	rsa_pub_unmap(dev, edesc, req);
 	rsa_io_unmap(dev, edesc, req);
@@ -135,7 +137,7 @@ static void rsa_pub_done(struct device *dev, u32 *desc, u32 err, void *context)
 	 * If no backlog flag, the completion of the request is done
 	 * by CAAM, not crypto engine.
 	 */
-	if (!edesc->bklog)
+	if (!has_bklog)
 		akcipher_request_complete(req, ecode);
 	else
 		crypto_finalize_akcipher_request(jrp->engine, req, ecode);
@@ -152,11 +154,13 @@ static void rsa_priv_f_done(struct device *dev, u32 *desc, u32 err,
 	struct caam_rsa_req_ctx *req_ctx = akcipher_request_ctx(req);
 	struct rsa_edesc *edesc;
 	int ecode = 0;
+	bool has_bklog;
 
 	if (err)
 		ecode = caam_jr_strstatus(dev, err);
 
 	edesc = req_ctx->edesc;
+	has_bklog = edesc->bklog;
 
 	switch (key->priv_form) {
 	case FORM1:
@@ -176,7 +180,7 @@ static void rsa_priv_f_done(struct device *dev, u32 *desc, u32 err,
 	 * If no backlog flag, the completion of the request is done
 	 * by CAAM, not crypto engine.
 	 */
-	if (!edesc->bklog)
+	if (!has_bklog)
 		akcipher_request_complete(req, ecode);
 	else
 		crypto_finalize_akcipher_request(jrp->engine, req, ecode);