[PATCH 1/2] mtd: spi-nor: sfdp: check the length of the xSPI Profile 1.0 table

[HyeongJun An <sammiee5311@gmail.com>]

spi_nor_parse_profile1() sizes its bounce buffer from the length the
flash reports in the SFDP parameter header, then indexes that buffer at
fixed offsets:

    len = profile1_header->length * sizeof(*dwords);
    dwords = kmalloc(len, GFP_KERNEL);
    ...
    dummy = FIELD_GET(PROFILE1_DWORD5_DUMMY_166MHZ, dwords[SFDP_DWORD(5)]);

The parser reads up to DWORD5, but never checks that the table is that
long.  The length is a u8 the flash supplies, so a device advertising
the table 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(5)]
reads sixteen bytes beyond it.  A length of zero is worse, as kmalloc()
then returns ZERO_SIZE_PTR rather than an error and the first access
dereferences it.

The bytes read out of bounds are not just discarded either, they end up
as the dummy cycle count programmed for 8D-8D-8D fast reads.

SFDP tables that do not match what the flash actually implements are
common enough that this file already carries fixup hooks for them, and
malformed SFDP has caused memory-safety bugs here before.  See
commit f0f0cfdc3a02 ("mtd: spi-nor: Fix shift-out-of-bounds in
spi_nor_set_erase_type").

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.

Fixes: fb27f198971a ("mtd: spi-nor: sfdp: parse xSPI Profile 1.0 table")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: HyeongJun An <sammiee5311@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 4600983cb579..d3d85b5d1b4a 100644
--- a/drivers/mtd/spi-nor/sfdp.c
+++ b/drivers/mtd/spi-nor/sfdp.c
@@ -1175,6 +1175,7 @@ static int spi_nor_parse_4bait(struct spi_nor *nor,
 #define PROFILE1_DWORD5_DUMMY_166MHZ		GENMASK(31, 27)
 #define PROFILE1_DWORD5_DUMMY_133MHZ		GENMASK(21, 17)
 #define PROFILE1_DWORD5_DUMMY_100MHZ		GENMASK(11, 7)
+#define SFDP_PROFILE1_DWORD_MAX			5
 
 /**
  * spi_nor_parse_profile1() - parse the xSPI Profile 1.0 table
@@ -1192,6 +1193,9 @@ static int spi_nor_parse_profile1(struct spi_nor *nor,
 	int ret;
 	u8 dummy, opcode;
 
+	if (profile1_header->length < SFDP_PROFILE1_DWORD_MAX)
+		return -EINVAL;
+
 	len = profile1_header->length * sizeof(*dwords);
 	dwords = kmalloc(len, GFP_KERNEL);
 	if (!dwords)
-- 
2.43.0