Messages in this thread | | | Date | Thu, 19 Jun 2014 03:41:24 +0200 | From | Heinrich Schuchardt <> | Subject | Re: [PATCH 1/1] media: dib9000: avoid out of bound access |
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On 19.06.2014 01:50, Kees Cook wrote: > On Wed, Jun 18, 2014 at 3:02 PM, Heinrich Schuchardt <xypron.glpk@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.glpk@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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