* Fix a stack overflow in lib/bch.c

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Merge tag 'mtd/fixes-for-4.19-rc8' of git://git.infradead.org/linux-mtd

Boris writes:
  "mdt: fix for 4.19-rc8

   * Fix a stack overflow in lib/bch.c"

* tag 'mtd/fixes-for-4.19-rc8' of git://git.infradead.org/linux-mtd:
  lib/bch: fix possible stack overrun

lib/Makefile

@@ -119,7 +119,6 @@ obj-$(CONFIG_ZLIB_INFLATE) += zlib_inflate/
 obj-$(CONFIG_ZLIB_DEFLATE) += zlib_deflate/
 obj-$(CONFIG_REED_SOLOMON) += reed_solomon/
 obj-$(CONFIG_BCH) += bch.o
-CFLAGS_bch.o := $(call cc-option,-Wframe-larger-than=4500)
 obj-$(CONFIG_LZO_COMPRESS) += lzo/
 obj-$(CONFIG_LZO_DECOMPRESS) += lzo/
 obj-$(CONFIG_LZ4_COMPRESS) += lz4/

lib/bch.c

@@ -79,20 +79,19 @@
 #define GF_T(_p)               (CONFIG_BCH_CONST_T)
 #define GF_N(_p)               ((1 << (CONFIG_BCH_CONST_M))-1)
 #define BCH_MAX_M              (CONFIG_BCH_CONST_M)
+#define BCH_MAX_T	       (CONFIG_BCH_CONST_T)
 #else
 #define GF_M(_p)               ((_p)->m)
 #define GF_T(_p)               ((_p)->t)
 #define GF_N(_p)               ((_p)->n)
-#define BCH_MAX_M              15
+#define BCH_MAX_M              15 /* 2KB */
+#define BCH_MAX_T              64 /* 64 bit correction */
 #endif
 
-#define BCH_MAX_T              (((1 << BCH_MAX_M) - 1) / BCH_MAX_M)
-
 #define BCH_ECC_WORDS(_p)      DIV_ROUND_UP(GF_M(_p)*GF_T(_p), 32)
 #define BCH_ECC_BYTES(_p)      DIV_ROUND_UP(GF_M(_p)*GF_T(_p), 8)
 
 #define BCH_ECC_MAX_WORDS      DIV_ROUND_UP(BCH_MAX_M * BCH_MAX_T, 32)
-#define BCH_ECC_MAX_BYTES      DIV_ROUND_UP(BCH_MAX_M * BCH_MAX_T, 8)
 
 #ifndef dbg
 #define dbg(_fmt, args...)     do {} while (0)
@@ -202,6 +201,9 @@ void encode_bch(struct bch_control *bch, const uint8_t *data,
 	const uint32_t * const tab3 = tab2 + 256*(l+1);
 	const uint32_t *pdata, *p0, *p1, *p2, *p3;
 
+	if (WARN_ON(r_bytes > sizeof(r)))
+		return;
+
 	if (ecc) {
 		/* load ecc parity bytes into internal 32-bit buffer */
 		load_ecc8(bch, bch->ecc_buf, ecc);
@@ -1285,6 +1287,13 @@ struct bch_control *init_bch(int m, int t, unsigned int prim_poly)
 		 */
 		goto fail;
 
+	if (t > BCH_MAX_T)
+		/*
+		 * we can support larger than 64 bits if necessary, at the
+		 * cost of higher stack usage.
+		 */
+		goto fail;
+
 	/* sanity checks */
 	if ((t < 1) || (m*t >= ((1 << m)-1)))
 		/* invalid t value */