On Wed, Mar 17, 2021 at 7:27 PM Gustavo A. R. Silva
<gust...@embeddedor.com> wrote:
> On 3/17/21 12:11, Jann Horn wrote:
> > On Wed, Mar 17, 2021 at 8:43 AM Gustavo A. R. Silva
> > <gustavo...@kernel.org> wrote:
> >> Fix the following out-of-bounds warning by replacing the one-element
> >> array in an anonymous union with a pointer:
> >>
> >> CC [M] drivers/net/ethernet/intel/ixgbe/ixgbe_common.o
> >> drivers/net/ethernet/intel/ixgbe/ixgbe_common.c: In function
> >> ‘ixgbe_host_interface_command’:
> >> drivers/net/ethernet/intel/ixgbe/ixgbe_common.c:3729:13: warning: array
> >> subscript 1 is above array bounds of ‘u32[1]’ {aka ‘unsigned int[1]’}
> >> [-Warray-bounds]
> >> 3729 | bp->u32arr[bi] = IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG, bi);
> >> | ~~~~~~~~~~^~~~
> >> drivers/net/ethernet/intel/ixgbe/ixgbe_common.c:3682:7: note: while
> >> referencing ‘u32arr’
> >> 3682 | u32 u32arr[1];
> >> | ^~~~~~
> >>
> >> This helps with the ongoing efforts to globally enable -Warray-bounds.
> >>
> >> Notice that, the usual approach to fix these sorts of issues is to
> >> replace the one-element array with a flexible-array member. However,
> >> flexible arrays should not be used in unions. That, together with the
> >> fact that the array notation is not being affected in any ways, is why
> >> the pointer approach was chosen in this case.
> >>
> >> Link: https://github.com/KSPP/linux/issues/109
> >> Signed-off-by: Gustavo A. R. Silva <gustavo...@kernel.org>
> >> ---
> >> drivers/net/ethernet/intel/ixgbe/ixgbe_common.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
> >> b/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
> >> index 62ddb452f862..bff3dc1af702 100644
> >> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
> >> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
> >> @@ -3679,7 +3679,7 @@ s32 ixgbe_host_interface_command(struct ixgbe_hw
> >> *hw, void *buffer,
> >> u32 hdr_size = sizeof(struct ixgbe_hic_hdr);
> >> union {
> >> struct ixgbe_hic_hdr hdr;
> >> - u32 u32arr[1];
> >> + u32 *u32arr;
> >> } *bp = buffer;
> >> u16 buf_len, dword_len;
> >> s32 status;
> >
> > This looks bogus. An array is inline, a pointer points elsewhere -
> > they're not interchangeable.
>
> Yep; but in this case these are the only places in the code where _u32arr_ is
> being used:
>
> 3707 /* first pull in the header so we know the buffer length */
> 3708 for (bi = 0; bi < dword_len; bi++) {
> 3709 bp->u32arr[bi] = IXGBE_READ_REG_ARRAY(hw,
> IXGBE_FLEX_MNG, bi);
> 3710 le32_to_cpus(&bp->u32arr[bi]);
> 3711 }
So now line 3709 means: Read a pointer from bp->u32arr (the value
being read from there is not actually a valid pointer), and write to
that pointer at offset `bi`. I don't see how that line could execute
without crashing.
