Re: [PATCH RFC] brcmfmac: sanitize DMI strings v2

From: Hans de Goede
Date: Mon May 06 2019 - 06:35:02 EST


On 06-05-19 12:20, Victor Bravo wrote:
On Mon, May 06, 2019 at 11:33:20AM +0200, Hans de Goede wrote:

On 06-05-19 11:06, Victor Bravo wrote:
On Mon, May 06, 2019 at 10:13:38AM +0200, Hans de Goede wrote:


On 05-05-19 17:03, Victor Bravo wrote:
Sanitize DMI strings in brcmfmac driver to make resulting filenames
contain only safe characters. This version replaces all non-printable
characters incl. delete (0-31, 127-255), spaces and slashes with

This change breaks backward compatibility, but adds control over strings
passed to firmware loader and compatibility with CONFIG_EXTRA_FIRMWARE
which doesn't support spaces in filenames.

Changes from v1: don't revert fresh commit by someone else

Signed-off-by: Victor Bravo <1905@xxxxxxxxxx>

Thank you for the patch, but I'm sorry to say this patch cannot go in as is,
because it will break existing systems.

If you look here:

You will see a file named: "brcmfmac43430a0-sdio.ONDA-V80 PLUS.txt" there, which
has a space in its name (and which works fine).

Thanks for the updates. Spaces are actually a problem as files with spaces
don't work when built-in with CONFIG_EXTRA_FIRMWARE (which is used with
non-modular kernel containing brcmfmac driver).

If the DMI string contains slashes, they will cause problems
for obvious reasons too.

Right, as said I'm fine with sanitizing the names, so dropping e.g. / chars,
but replacing space with _ will cause wifi to stop working on Onda V80 Plus devices and
we have a clear no regressions policy in the kernel.

Please keep in mind that dropping slashes and non-printable characters
might be a regression too, as some users may already be using
intermediate directories or filenames with tabs etc. if their DMI
strings contain these. If such users exist, they will have to rename
their nvram files anyway.

I consider it very unlikely that such users exist OTOH the Onda V80 PLus
nvram file is actually in linux-firmware upstream, so that e.g. Fedora 30
has working wifi OOTB on the V80 Plus, if we go with your proposal to
also replace spaces, then users with a V80 Plus will all of a sudden have
their wifi stop working.

If Kalle and Arend are in favor of including space in the "bad character"
list then at a minimum we must first get a patch added to linux-firmware
adding an ONDA-V80_PLUS.txt symlink to the ONDA-V80 PLUS.txt file.

On the other hand, removing just slashes and non-printable characters
(i.e. (*dst < 0x20) || (dst == '/') || (dst == 0x7f)) would allow
the sanitize function to the bit array and go with hardcoded conditions
(especially if those are final and won't need further adjustments in
set of allowed characters

If we're going to do some filtering, then I suggest we play it safe and also
disallow other chars which may be used as a separator somewhere, specifically
':' and ','.

Currently upstream linux-firmware has these files which rely on the DMI

brcmfmac43430a0-sdio.ONDA-V80 PLUS.txt

The others are either part of the DMI override table for devices with unsuitable
DMI strings like "Default String"; or are device-tree based.

So as long as we don't break those 3 (or break the ONDA one but get a symlink
in place) we can sanitize a bit more then just non-printable and '/'.

Kalle, Arend, what is your opinion on this?

Note I do not expect the ONDA V80 Plus to have a lot of Linux users, but it definitely has some.



I'm fine with doing some sanitizing of the strings, but replacing spaces with _
breaks existing use-cases (will cause a regression for them) and a space is absolutely
a valid character in a filename and the firmware-loader can deal with this just fine.

If the code for building firmwares into the kernel cannot deal with spaces then IMHO
that code should be fixed instead. Have you looked into fixing that?

Yes, but updating CONFIG_EXTRA_FIRMWARE to support spaces because of
this looks much like

<snip off-topic remark>

Do you really think it's a good idea to propose that in
this case?

I think expecting spaces in filenames to just work is quite reasonable, after all
its been a long time since we've left DOS-es 8.3 filename limitations.

Have you actually looked at how hard it would be to make filenames with spaces work

No matter how you spin it, the space problem is a CONFIG_EXTRA_FIRMWARE bug, not an
issue with the brcmfmac code.

Well CONFIG_EXTRA_FIRMWARE is defined to use space as filename
separator, so I don't really dare to call that a bug. Also brcmfmac
seems to be only driver requiring support for spaces etc. in firmware
file names, and this requirement seems to be quite fresh.

So to me the proper way to fix this via CONFIG_EXTRA_FIRMWARE seems to

1) wait some time until brcfmac's fw filenames with spaces become
de-facto standard and distros are literally full of these.

2) after this happens, propose update of CONFIG_EXTRA_FIRMWARE to
support spaces in filenames, arguing with status quo which coming from 1)

Unfortunately I feel more like a programmer and this seems more like
politics, so I can promise participation in the wait part only right

As for your T100HA example from earlier in this thread, the brcmfmac driver now
also supports getting the firmware from a special EFI nvram variable, which the
T100HA sets, so you do not need to provide a nvram file on the T100HA and things
will still work.

I don't really get this. Can you please suggest how do I make the driver
use something different than "brcmfmac43340-sdio.txt" or
"brcmfmac43340-sdio.ASUSTeK COMPUTER INC.-T100HAN.txt" on T100HAN?

If you leave out either file, then with a recent kernel you should see this
brcm_info trigger:

brcmf_info("Using nvram EFI variable\n");

So you should see this message when you do:

dmesg | grep "Using nvram EFI variable"

And the wifi on the T100HAN should just work, without needing to do any
manual config / provide an nvram file in anyway.

I always strive to make hardware just work with Linux and any UEFI x86 machine
using brcmfmac which provides the necessary nvram EFI variable in its firmware
should now just work when booting say a Fedora 30 livecd.

The EFI nvram var support has been tested successfully on the following models:

Acer Iconia Tab8 w1-8
Acer One 10
Asus T100CHI
Asus T100HA
Asus T100TA
Asus T200TA
Lenovo Mixx 2 8
Lenovo Yoga2 tablet 10

Thanks! Wasn't aware of this, will try in the evening.




diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/dmi.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/dmi.c
index 7535cb0d4ac0..84571e09b465 100644
--- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/dmi.c
+++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/dmi.c
@@ -23,6 +23,14 @@
/* The DMI data never changes so we can use a static buf for this */
static char dmi_board_type[128];
+/* Array of 128 bits representing 7-bit characters allowed in DMI strings. */
+static unsigned char brcmf_dmi_allowed_chars[] = {
+ 0x00, 0x00, 0x00, 0x00, 0xfe, 0x7f, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f
+#define BRCMF_DMI_SAFE_CHAR '_'
struct brcmf_dmi_data {
u32 chip;
u32 chiprev;
@@ -99,6 +107,15 @@ static const struct dmi_system_id dmi_platform_data[] = {
+void brcmf_dmi_sanitize(char *dst, const unsigned char *allowed, char safe)
+ while (*dst) {
+ if ((*dst < 0) || !(allowed[*dst / 8] & (1 << (*dst % 8))))

At a first look I have no clue what this code is doing and I honestly do not feel
like figuring it out, this is clever, but IMHO not readable.

Understood. The cluless part actually checks corresponding bit
in allowed array, which is a bit mask describing what characters
are allowed or not.

Please just write this as if (*dst < 0x21 || (*dst > foo && < bar) || etc,
so that a human can actually see in one look what the code is doing.

You may want to wait for Arend to give his opinion before changing this though,
maybe he likes the code as is.

Also note that that should be < 0x20 of course, since we need to preserve spaces
as is to avoid a regression.

This has been already discussed, spaces are a problem. There even was an
opinion that adding the code that doesn't bother with spaces and slashes
might be a regression as well.





+ *dst = safe;
+ dst++;
+ }
void brcmf_dmi_probe(struct brcmf_mp_device *settings, u32 chip, u32 chiprev)
const struct dmi_system_id *match;
@@ -126,6 +143,9 @@ void brcmf_dmi_probe(struct brcmf_mp_device *settings, u32 chip, u32 chiprev)
if (sys_vendor && product_name) {
snprintf(dmi_board_type, sizeof(dmi_board_type), "%s-%s",
sys_vendor, product_name);
+ brcmf_dmi_sanitize(dmi_board_type,
+ brcmf_dmi_allowed_chars,
settings->board_type = dmi_board_type;