[PATCH v2] mtd: gpmi: Fix NULL pointer dereference

[Fabio Estevam <festevam@gmail.com>]

From: Fabio Estevam <fabio.estevam@freescale.com>

Currently mx23_check_transcription_stamp() uses chip->buffers->databuf
as its buffer, which is allocated by nand_scan_tail().

Since commit 720e7ce5 ("mtd: gpmi: remove the nand_scan()"), 
mx23_check_transcription_stamp() is called before nand_scan_tail(), which causes
a NULL pointer dereference:

[    1.150000] NAND device: Manufacturer ID: 0xec, Chip ID: 0xd7 (Samsung NAND 4GiB 3,3V 8-bit), 4096MiB, page size: 4096, OOB size: 8
[    1.160000] Unable to handle kernel NULL pointer dereference at virtual address 000005d0
[    1.170000] pgd = c0004000
[    1.170000] [000005d0] *pgd=00000000
[    1.180000] Internal error: Oops: 5 [#1] ARM
[    1.180000] Modules linked in:
[    1.180000] CPU: 0 PID: 1 Comm: swapper Not tainted 3.12.0 #89
[    1.180000] task: c7440000 ti: c743a000 task.ti: c743a000
[    1.180000] PC is at memcmp+0x10/0x54
[    1.180000] LR is at gpmi_nand_probe+0x42c/0x894
[    1.180000] pc : [<c025fcb0>]    lr : [<c02f6a68>]    psr: 20000053
[    1.180000] sp : c743be2c  ip : 600000d3  fp : ffffffff
[    1.180000] r10: 000005d0  r9 : c02f5f08  r8 : 00000000
[    1.180000] r7 : c75858a8  r6 : c75858a8  r5 : c7585b18  r4 : c7585800
[    1.180000] r3 : 000005d0  r2 : 00000004  r1 : c05c33e4  r0 : 000005d0
[    1.180000] Flags: nzCv  IRQs on  FIQs off  Mode SVC_32  ISA ARM  Segment kernel
[    1.180000] Control: 0005317f  Table: 40004000  DAC: 00000017
[    1.180000] Process swapper (pid: 1, stack limit = 0xc743a1c0)

In order to fix this problem, allocate the buffer locally via kzalloc().

Also, as mx23_check_transcription_stamp() can return en error code now, adapt
the logic in mx23_boot_init() to take this into account.

Cc: <stable@vger.kernel.org> # 3.12
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
---
Changes since v1:
- Drop sizeof(*buffer) from size calculatio in kzalloc (Brian Norris)
- Propagate the error if mx23_check_transcription_stamp returns a negative
error code (Brian Norris)

 drivers/mtd/nand/gpmi-nand/gpmi-nand.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
index a9830ff..f99b876 100644
--- a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
+++ b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
@@ -1342,7 +1342,7 @@ static int mx23_check_transcription_stamp(struct gpmi_nand_data *this)
 	unsigned int search_area_size_in_strides;
 	unsigned int stride;
 	unsigned int page;
-	uint8_t *buffer = chip->buffers->databuf;
+	uint8_t *buffer;
 	int saved_chip_number;
 	int found_an_ncb_fingerprint = false;
 
@@ -1352,6 +1352,9 @@ static int mx23_check_transcription_stamp(struct gpmi_nand_data *this)
 	saved_chip_number = this->current_chip;
 	chip->select_chip(mtd, 0);
 
+	buffer = kzalloc(strlen(fingerprint), GFP_KERNEL);
+	if (!buffer)
+		return -ENOMEM;
 	/*
 	 * Loop through the first search area, looking for the NCB fingerprint.
 	 */
@@ -1380,6 +1383,8 @@ static int mx23_check_transcription_stamp(struct gpmi_nand_data *this)
 
 	chip->select_chip(mtd, saved_chip_number);
 
+	kfree(buffer);
+
 	if (found_an_ncb_fingerprint)
 		dev_dbg(dev, "\tFound a fingerprint\n");
 	else
@@ -1488,7 +1493,11 @@ static int mx23_boot_init(struct gpmi_nand_data  *this)
 	 * transcription stamp. If we find it, then we don't have to do
 	 * anything -- the block marks are already transcribed.
 	 */
-	if (mx23_check_transcription_stamp(this))
+
+	ret = mx23_check_transcription_stamp(this);
+	if (ret < 0)
+		return ret;
+	else if (ret)
 		return 0;
 
 	/*
-- 
1.8.1.2