mtd: cfi_cmdset_0002: fix crash when erasing/writing AMD cards

stable inclusion
from stable-5.10.61
commit 779a0f4347a474cf4b503350f3eef682404b6779
bugzilla: 177029 https://gitee.com/openeuler/kernel/issues/I4EAXD

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=779a0f4347a474cf4b503350f3eef682404b6779

--------------------------------

commit 2394e628 upstream.

Erasing an AMD linear flash card (AM29F016D) crashes after the first
sector has been erased. Likewise, writing to it crashes after two bytes
have been written. The reason is a missing check for a null pointer -
the cmdset_priv field is not set for this type of card.

Fixes: 4844ef80 ("mtd: cfi_cmdset_0002: Add support for polling status register")
Signed-off-by: NAndreas Persson <andreasp56@outlook.com>
Signed-off-by: NMiquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/DB6P189MB05830B3530B8087476C5CFE4C1159@DB6P189MB0583.EURP189.PROD.OUTLOOK.COMSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/mtd/chips/cfi_cmdset_0002.c

@@ -119,7 +119,7 @@ static int cfi_use_status_reg(struct cfi_private *cfi)
 	struct cfi_pri_amdstd *extp = cfi->cmdset_priv;
 	u8 poll_mask = CFI_POLL_STATUS_REG | CFI_POLL_DQ;
 
-	return extp->MinorVersion >= '5' &&
+	return extp && extp->MinorVersion >= '5' &&
 		(extp->SoftwareFeatures & poll_mask) == CFI_POLL_STATUS_REG;
 }