[PATCH 2/2] mtd: spi-nor: sfdp: check the length of the SCCR map

[HyeongJun An]

spi_nor_parse_sccr() sizes its bounce buffer from the length the flash
reports in the SFDP parameter header, then reads DWORD22 out of it:

    len = sccr_header->length * sizeof(*dwords);
    dwords = kmalloc(len, GFP_KERNEL);
    ...
    if (FIELD_GET(SCCR_DWORD22_OCTAL_DTR_EN_VOLATILE,
                  dwords[SFDP_DWORD(22)]))

Nothing checks that the table actually has 22 DWORDs.  The length is a
u8 the flash supplies, so a device advertising the SCCR map with a
shorter length makes the read run past the allocation: with a length of
one the buffer is four bytes and dwords[SFDP_DWORD(22)] reads
eighty-four bytes beyond it.  A length of zero is worse, as kmalloc()
then returns ZERO_SIZE_PTR rather than an error and the read of
dwords[SFDP_DWORD(1)] dereferences it.

Reject a table shorter than the highest DWORD the parser reads, the way
spi_nor_parse_4bait() already does with SFDP_4BAIT_DWORD_MAX.  Failing
an optional parameter table is not fatal: spi_nor_parse_sfdp() warns and
carries on with the data gathered so far.

spi_nor_parse_sccr_mc() does not need the same check.  It derives the
number of dice from the length it allocated with, so its highest index
stays inside the buffer, and a length below two leaves its loop empty.

Fixes: 7ab8b810757a ("mtd: spi-nor: sfdp: Add support for SCCR map for multi-chip device")
Cc: stable at vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: HyeongJun An <sammiee5311 at gmail.com>
---
 drivers/mtd/spi-nor/sfdp.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/mtd/spi-nor/sfdp.c b/drivers/mtd/spi-nor/sfdp.c
index d3d85b5d1b4a..6c9db103a29a 100644
--- a/drivers/mtd/spi-nor/sfdp.c
+++ b/drivers/mtd/spi-nor/sfdp.c
@@ -1266,6 +1266,7 @@ static int spi_nor_parse_profile1(struct spi_nor *nor,
 }
 
 #define SCCR_DWORD22_OCTAL_DTR_EN_VOLATILE		BIT(31)
+#define SFDP_SCCR_DWORD_MAX				22
 
 /**
  * spi_nor_parse_sccr() - Parse the Status, Control and Configuration Register
@@ -1284,6 +1285,9 @@ static int spi_nor_parse_sccr(struct spi_nor *nor,
 	size_t len;
 	int ret;
 
+	if (sccr_header->length < SFDP_SCCR_DWORD_MAX)
+		return -EINVAL;
+
 	len = sccr_header->length * sizeof(*dwords);
 	dwords = kmalloc(len, GFP_KERNEL);
 	if (!dwords)
-- 
2.43.0