On 19.06.2014 01:50, Kees Cook wrote:
On Wed, Jun 18, 2014 at 3:02 PM, Heinrich Schuchardt <xypron.g...@gmx.de> wrote:
The current test to avoid out of bound access to mb[] is insufficient.
For len = 19 non-existent mb[10] will be accessed.
A check in the for loop is insufficient to avoid out of bound access in
dib9000_mbx_send_attr.
Signed-off-by: Heinrich Schuchardt <xypron.g...@gmx.de>
---
drivers/media/dvb-frontends/dib9000.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/media/dvb-frontends/dib9000.c
b/drivers/media/dvb-frontends/dib9000.c
index e540cfb..6a71917 100644
--- a/drivers/media/dvb-frontends/dib9000.c
+++ b/drivers/media/dvb-frontends/dib9000.c
@@ -1040,10 +1040,13 @@ static int dib9000_risc_apb_access_write(struct
dib9000_state *state, u32 addres
if (address >= 1024 || !state->platform.risc.fw_is_running)
return -EINVAL;
+ if (len > 18)
+ return -EINVAL;
+
/* dprintk( "APB access thru wr fw %d %x", address, attribute); */
mb[0] = (unsigned short)address;
- for (i = 0; i < len && i < 20; i += 2)
+ for (i = 0; i < len; i += 2)
mb[1 + (i / 2)] = (b[i] << 8 | b[i + 1]);
Good catch on the mb[] access! However, I think there is still more to
fix since b[i + 1] can read past the end of b: Say b is defined as "u8
b[3]". Passing len 3 means the second loop, with i==2 will access b[2]
and b[3], the latter is out of range.
b[] and len are provided by the caller of dib9000_risc_apb_access_write.
dib9000_risc_apb_access_write cannot verify if the length of b[] matches
len at all.
Currently dib9000_risc_apb_access_write cannot handle odd values of len.
This holds even true if b[] has been padded with zero to an even length:
For odd values of len the last byte is not passed to dib9000_mbx_send_attr.
What is left unclear is how odd values of len should be handled correctly:
Should the caller provide a b[] padded with 0 to the next even number of
bytes,
or should dib9000_risc_apb_access_write take care not to read more then
len bytes,
or should odd values of len cause an error EINVAL.
From what I read in the coding one source of the value of len is
tuner_attach(), which is called from outside the dib9000 driver.
Heinrich
-Kees
dib9000_mbx_send_attr(state, OUT_MSG_BRIDGE_APB_W, mb, 1 + len / 2,
attribute);
--
2.0.0
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