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Subject[PATCH v3/resubmit 1/3] staging: gs_fpgaboot: add buffer overflow checks
Date
Four fields in struct fpgaimage are char arrays of length MAX_STR (256).
The amount of data read into these buffers is controlled by a length
field in the bitstream file read from userspace. If a corrupt or
malicious firmware file was supplied, kernel data beyond these buffers
can be overwritten arbitrarily.

This patch adds a check of the bitstream's length value to ensure it
fits within the bounds of the allocated buffers. An error condition is
returned from gs_read_bitstream if any of the reads fail.

Signed-off-by: Jacob von Chorus <jacobvonchorus@cwphoto.ca>
---
v3:
- use >= to prevent an integer overflow in the comparison
- use get_unaligned_be functions to interpret length fields
- fix remainder of file to use valid error codes

v2:
- char arrays converted to u8 arrays
- replace error return value with proper error code in
gs_read_bitstream

drivers/staging/gs_fpgaboot/gs_fpgaboot.c | 54 +++++++++++++++++++++++--------
1 file changed, 40 insertions(+), 14 deletions(-)

diff --git a/drivers/staging/gs_fpgaboot/gs_fpgaboot.c b/drivers/staging/gs_fpgaboot/gs_fpgaboot.c
index 19b550fff0..a49019af60 100644
--- a/drivers/staging/gs_fpgaboot/gs_fpgaboot.c
+++ b/drivers/staging/gs_fpgaboot/gs_fpgaboot.c
@@ -23,6 +23,7 @@
#include <linux/delay.h>
#include <linux/io.h>
#include <linux/firmware.h>
+#include <asm/unaligned.h>

#include "gs_fpgaboot.h"
#include "io.h"
@@ -47,7 +48,7 @@ static void read_bitstream(char *bitdata, char *buf, int *offset, int rdsize)
*offset += rdsize;
}

-static void readinfo_bitstream(char *bitdata, char *buf, int *offset)
+static int readinfo_bitstream(char *bitdata, char *buf, int size, int *offset)
{
char tbuf[64];
s32 len;
@@ -58,10 +59,16 @@ static void readinfo_bitstream(char *bitdata, char *buf, int *offset)
/* read length */
read_bitstream(bitdata, tbuf, offset, 2);

- len = tbuf[0] << 8 | tbuf[1];
+ len = get_unaligned_be16(tbuf);
+ if (len >= size) {
+ pr_err("error: readinfo buffer too small\n");
+ return -EINVAL;
+ }

read_bitstream(bitdata, buf, offset, len);
buf[len] = '\0';
+
+ return 0;
}

/*
@@ -83,8 +90,7 @@ static int readlength_bitstream(char *bitdata, int *lendata, int *offset)
/* read 4bytes length */
read_bitstream(bitdata, tbuf, offset, 4);

- *lendata = tbuf[0] << 24 | tbuf[1] << 16 |
- tbuf[2] << 8 | tbuf[3];
+ *lendata = get_unaligned_be32(tbuf);

return 0;
}
@@ -113,7 +119,7 @@ static int readmagic_bitstream(char *bitdata, int *offset)
/*
* NOTE: supports only bitstream format
*/
-static enum fmt_image get_imageformat(struct fpgaimage *fimage)
+static enum fmt_image get_imageformat(void)
{
return f_bit;
}
@@ -127,34 +133,54 @@ static void gs_print_header(struct fpgaimage *fimage)
pr_info("lendata: %d\n", fimage->lendata);
}

-static void gs_read_bitstream(struct fpgaimage *fimage)
+static int gs_read_bitstream(struct fpgaimage *fimage)
{
char *bitdata;
int offset;
+ int err;

offset = 0;
bitdata = (char *)fimage->fw_entry->data;

- readmagic_bitstream(bitdata, &offset);
- readinfo_bitstream(bitdata, fimage->filename, &offset);
- readinfo_bitstream(bitdata, fimage->part, &offset);
- readinfo_bitstream(bitdata, fimage->date, &offset);
- readinfo_bitstream(bitdata, fimage->time, &offset);
- readlength_bitstream(bitdata, &fimage->lendata, &offset);
+ err = readmagic_bitstream(bitdata, &offset);
+ if (err)
+ return err;
+
+ err = readinfo_bitstream(bitdata, fimage->filename, MAX_STR, &offset);
+ if (err)
+ return err;
+ err = readinfo_bitstream(bitdata, fimage->part, MAX_STR, &offset);
+ if (err)
+ return err;
+ err = readinfo_bitstream(bitdata, fimage->date, MAX_STR, &offset);
+ if (err)
+ return err;
+ err = readinfo_bitstream(bitdata, fimage->time, MAX_STR, &offset);
+ if (err)
+ return err;
+
+ err = readlength_bitstream(bitdata, &fimage->lendata, &offset);
+ if (err)
+ return err;

fimage->fpgadata = bitdata + offset;
+
+ return 0;
}

static int gs_read_image(struct fpgaimage *fimage)
{
int img_fmt;
+ int err;

- img_fmt = get_imageformat(fimage);
+ img_fmt = get_imageformat();

switch (img_fmt) {
case f_bit:
pr_info("image is bitstream format\n");
- gs_read_bitstream(fimage);
+ err = gs_read_bitstream(fimage);
+ if (err)
+ return err;
break;
default:
pr_err("unsupported fpga image format\n");
--
2.11.0
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