* [PATCH] Verify memory sizes on 32 bit systems.
@ 2018-07-30 19:01 Tobias Stoeckmann
2018-08-03 21:07 ` Lucas De Marchi
0 siblings, 1 reply; 5+ messages in thread
From: Tobias Stoeckmann @ 2018-07-30 19:01 UTC (permalink / raw)
To: linux-modules
Large file system support is activated by default, which means that
on 32 bit systems, off_t is 64 bit in size.
Using st.st_size or any other 64 bit variable with mmap can lead to
integer truncation and therefore insufficient memory mapping.
Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
---
libkmod/libkmod-file.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/libkmod/libkmod-file.c b/libkmod/libkmod-file.c
index 5eeba6a..86f34c6 100644
--- a/libkmod/libkmod-file.c
+++ b/libkmod/libkmod-file.c
@@ -255,6 +255,8 @@ static int load_reg(struct kmod_file *file)
return -errno;
file->size = st.st_size;
+ if ((uintmax_t)st.st_size > (uintmax_t)SIZE_MAX)
+ return -EFBIG;
file->memory = mmap(NULL, file->size, PROT_READ, MAP_PRIVATE,
file->fd, 0);
if (file->memory == MAP_FAILED)
--
2.13.2
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] Verify memory sizes on 32 bit systems.
2018-07-30 19:01 [PATCH] Verify memory sizes on 32 bit systems Tobias Stoeckmann
@ 2018-08-03 21:07 ` Lucas De Marchi
2018-08-03 21:10 ` Tobias Stoeckmann
0 siblings, 1 reply; 5+ messages in thread
From: Lucas De Marchi @ 2018-08-03 21:07 UTC (permalink / raw)
To: Tobias Stoeckmann; +Cc: linux-modules
On Mon, Jul 30, 2018 at 12:02 PM Tobias Stoeckmann
<tobias@stoeckmann.org> wrote:
>
> Large file system support is activated by default, which means that
> on 32 bit systems, off_t is 64 bit in size.
>
> Using st.st_size or any other 64 bit variable with mmap can lead to
> integer truncation and therefore insufficient memory mapping.
>
> Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
> ---
> libkmod/libkmod-file.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/libkmod/libkmod-file.c b/libkmod/libkmod-file.c
> index 5eeba6a..86f34c6 100644
> --- a/libkmod/libkmod-file.c
> +++ b/libkmod/libkmod-file.c
> @@ -255,6 +255,8 @@ static int load_reg(struct kmod_file *file)
> return -errno;
>
> file->size = st.st_size;
> + if ((uintmax_t)st.st_size > (uintmax_t)SIZE_MAX)
why casting?
Lucas De Marchi
> + return -EFBIG;
> file->memory = mmap(NULL, file->size, PROT_READ, MAP_PRIVATE,
> file->fd, 0);
> if (file->memory == MAP_FAILED)
> --
> 2.13.2
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-modules" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
Lucas De Marchi
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] Verify memory sizes on 32 bit systems.
2018-08-03 21:07 ` Lucas De Marchi
@ 2018-08-03 21:10 ` Tobias Stoeckmann
2018-08-03 21:33 ` Lucas De Marchi
0 siblings, 1 reply; 5+ messages in thread
From: Tobias Stoeckmann @ 2018-08-03 21:10 UTC (permalink / raw)
To: Lucas De Marchi; +Cc: linux-modules
On Fri, Aug 03, 2018 at 02:07:34PM -0700, Lucas De Marchi wrote:
> > + if ((uintmax_t)st.st_size > (uintmax_t)SIZE_MAX)
>
> why casting?
Without casting, a warning could be triggered on 64 bit systems,
because on these systems a signed 64 bit int (off_t) is compared
with an unsigned 64 bit int (size_t) which could never be larger.
Casting it to uintmax_t, which is at least 64 bits in size,
silences this error.
No technical reason beyond that.
Tobias
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] Verify memory sizes on 32 bit systems.
2018-08-03 21:10 ` Tobias Stoeckmann
@ 2018-08-03 21:33 ` Lucas De Marchi
2018-08-03 21:51 ` Tobias Stoeckmann
0 siblings, 1 reply; 5+ messages in thread
From: Lucas De Marchi @ 2018-08-03 21:33 UTC (permalink / raw)
To: Tobias Stoeckmann; +Cc: linux-modules
On Fri, Aug 3, 2018 at 2:10 PM Tobias Stoeckmann <tobias@stoeckmann.org> wrote:
>
> On Fri, Aug 03, 2018 at 02:07:34PM -0700, Lucas De Marchi wrote:
> > > + if ((uintmax_t)st.st_size > (uintmax_t)SIZE_MAX)
> >
> > why casting?
>
> Without casting, a warning could be triggered on 64 bit systems,
> because on these systems a signed 64 bit int (off_t) is compared
> with an unsigned 64 bit int (size_t) which could never be larger.
>
> Casting it to uintmax_t, which is at least 64 bits in size,
> silences this error.
so you are casting the *sign* away, ok. But casting only st.st_size
should suffice.
Lucas De Marchi
>
> No technical reason beyond that.
>
>
> Tobias
--
Lucas De Marchi
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] Verify memory sizes on 32 bit systems.
2018-08-03 21:33 ` Lucas De Marchi
@ 2018-08-03 21:51 ` Tobias Stoeckmann
0 siblings, 0 replies; 5+ messages in thread
From: Tobias Stoeckmann @ 2018-08-03 21:51 UTC (permalink / raw)
To: Lucas De Marchi; +Cc: linux-modules
On Fri, Aug 03, 2018 at 02:33:51PM -0700, Lucas De Marchi wrote:
> so you are casting the *sign* away, ok. But casting only st.st_size
> should suffice.
I've just tried with some examples and I couldn't trigger the
warning which I have seen in other situations like this, i.e.
"always false due to limited range of data type".
If I cast the off_t to size_t, the compiler knows that it is not
possible that it could ever be larger than SIZE_MAX, optimizing
the block away. So I took uintmax_t.
But as long as there's no annoying warning, I am fine with just
casting st_size.
Tobias
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2018-08-03 21:51 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-07-30 19:01 [PATCH] Verify memory sizes on 32 bit systems Tobias Stoeckmann
2018-08-03 21:07 ` Lucas De Marchi
2018-08-03 21:10 ` Tobias Stoeckmann
2018-08-03 21:33 ` Lucas De Marchi
2018-08-03 21:51 ` Tobias Stoeckmann
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).