Re: [Outreachy kernel] [PATCH v2] staging: android: Replace strcpy with strlcpy
From: Julia Lawall
Date: Sat Mar 11 2017 - 16:35:10 EST
On Sun, 12 Mar 2017, SIMRAN SINGHAL wrote:
> On Sun, Mar 12, 2017 at 2:53 AM, Julia Lawall <julia.lawall@xxxxxxx> wrote:
> > On Sun, 12 Mar 2017, simran singhal wrote:
> >> Replace strcpy with strlcpy as strcpy does not check for buffer
> >> overflow.
> >> This is found using Flawfinder.
> >> Signed-off-by: simran singhal <singhalsimran0@xxxxxxxxx>
> >> ---
> >> v2:
> >> -Correcting the place of the parenthesis
> >> drivers/staging/android/ashmem.c | 3 ++-
> >> 1 file changed, 2 insertions(+), 1 deletion(-)
> >> diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
> >> index 7cbad0d..eb2f4ef 100644
> >> --- a/drivers/staging/android/ashmem.c
> >> +++ b/drivers/staging/android/ashmem.c
> >> @@ -548,7 +548,8 @@ static int set_name(struct ashmem_area *asma, void __user *name)
> >> if (unlikely(asma->file))
> >> ret = -EINVAL;
> >> else
> >> - strcpy(asma->name + ASHMEM_NAME_PREFIX_LEN, local_name);
> >> + strlcpy(asma->name + ASHMEM_NAME_PREFIX_LEN, local_name,
> >> + sizeof(asma->name + ASHMEM_NAME_PREFIX_LEN));
> > This appears to be the old patch.
> > Actually, looking closer, I don't think this is right at all. There seems
> > to be a goal of leaving some space at the beginning of asma->name. So the
> > amount of space available for local_name would be computed using a
> > subtraction, not an addition.
> Julia, By mistake I sent the wrong patch.
> And I am not getting you want to mention which space.
The following is the whole asma->name array. The | in the middle is the
offset ASHMEM_NAME_PREFIX_LEN. The xxx characters are in the
ASHMEM_NAME_PREFIX_LEN region. The space for local_name is only the part
indicates with the ys. This space is smaller than the size of asma->name.
In your calculation, you are allowing it to be larger. You will
potentially overflow the buffer by 2 * ASHMEM_NAME_PREFIX_LEN.