Re: [PATCH 3/4] firmware: actually return NULL on failed request_firmware_nowait()

[Kees Cook]

On Tue, Dec 8, 2015 at 6:38 PM, Brian Norris
<computersforpeace@xxxxxxxxx> wrote:
> The kerneldoc for request_firmware_nowait() says that it may call the
> provided cont() callback with @fw == NULL, if the firmware request
> fails. However, this is not the case when called with an empty string
> (""). This case is short-circuited by the 'name[0] == '\0'' check
> introduced in commit 471b095dfe0d ("firmware_class: make sure fw requests
> contain a name"), so _request_firmware() never gets to set the fw to
> NULL.
>
> Noticed while using the new 'trigger_async_request' testing hook:
>
>     # printf '\x00' > /sys/devices/virtual/misc/test_firmware/trigger_async_request
>     [10553.726178] test_firmware: loading ''
>     [10553.729859] test_firmware: loaded: 995209091
>     # printf '\x00' > /sys/devices/virtual/misc/test_firmware/trigger_async_request
>     [10733.676184] test_firmware: loading ''
>     [10733.679855] Unable to handle kernel NULL pointer dereference at virtual address 00000004
>     [10733.687951] pgd = ec188000
>     [10733.690655] [00000004] *pgd=00000000
>     [10733.694240] Internal error: Oops: 5 [#1] SMP ARM
>     [10733.698847] Modules linked in: btmrvl_sdio btmrvl bluetooth sbs_battery nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables asix usbnet mwifiex_sdio mwifiex cfg80211 jitterentropy_rng drbg joydev snd_seq_midi snd_seq_midi_event snd_rawmidi snd_seq snd_seq_device ppp_async ppp_generic slhc tun
>     [10733.725670] CPU: 0 PID: 6600 Comm: bash Not tainted 4.4.0-rc4-00351-g63d0877 #178
>     [10733.733137] Hardware name: Rockchip (Device Tree)
>     [10733.737831] task: ed24f6c0 ti: ee322000 task.ti: ee322000
>     [10733.743222] PC is at do_raw_spin_lock+0x18/0x1a0
>     [10733.747831] LR is at _raw_spin_lock+0x18/0x1c
>     [10733.752180] pc : [<c00653a0>]    lr : [<c054c204>]    psr: a00d0013
>     [10733.752180] sp : ee323df8  ip : ee323e20  fp : ee323e1c
>     [10733.763634] r10: 00000051  r9 : b6f18000  r8 : ee323f80
>     [10733.768847] r7 : c089cebc  r6 : 00000001  r5 : 00000000  r4 : ec0e6000
>     [10733.775360] r3 : dead4ead  r2 : c06bd140  r1 : eef913b4  r0 : 00000000
>     [10733.781874] Flags: NzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
>     [10733.788995] Control: 10c5387d  Table: 2c18806a  DAC: 00000051
>     [10733.794728] Process bash (pid: 6600, stack limit = 0xee322218)
>     [10733.800549] Stack: (0xee323df8 to 0xee324000)
>     [10733.804896] 3de0:                                                       ec0e6000 00000000
>     [10733.813059] 3e00: 00000001 c089cebc ee323f80 b6f18000 ee323e2c ee323e20 c054c204 c0065394
>     [10733.821221] 3e20: ee323e44 ee323e30 c02fec60 c054c1f8 ec0e7ec0 ec3fcfc0 ee323e5c ee323e48
>     [10733.829384] 3e40: c02fed08 c02fec48 c07dbf74 eeb05a00 ee323e8c ee323e60 c0253828 c02fecac
>     [10733.837547] 3e60: 00000001 c0116950 ee323eac ee323e78 00000001 ec3fce00 ed2d9700 ed2d970c
>     [10733.845710] 3e80: ee323e9c ee323e90 c02e873c c02537d4 ee323eac ee323ea0 c017bd40 c02e8720
>     [10733.853873] 3ea0: ee323ee4 ee323eb0 c017b250 c017bd00 00000000 00000000 f3e47a54 ec128b00
>     [10733.862035] 3ec0: c017b10c ee323f80 00000001 c000f504 ee322000 00000000 ee323f4c ee323ee8
>     [10733.870197] 3ee0: c011b71c c017b118 ee323fb0 c011bc90 becfa8d9 00000001 ec128b00 00000001
>     [10733.878359] 3f00: b6f18000 ee323f80 ee323f4c ee323f18 c011bc90 c0063950 ee323f3c ee323f28
>     [10733.886522] 3f20: c0063950 c0549138 00000001 ec128b00 00000001 ec128b00 b6f18000 ee323f80
>     [10733.894684] 3f40: ee323f7c ee323f50 c011bed8 c011b6ec c0135fb8 c0135f24 ec128b00 ec128b00
>     [10733.902847] 3f60: 00000001 b6f18000 c000f504 ee322000 ee323fa4 ee323f80 c011c664 c011be24
>     [10733.911009] 3f80: 00000000 00000000 00000001 b6f18000 b6e79be0 00000004 00000000 ee323fa8
>     [10733.919172] 3fa0: c000f340 c011c618 00000001 b6f18000 00000001 b6f18000 00000001 00000000
>     [10733.927334] 3fc0: 00000001 b6f18000 b6e79be0 00000004 00000001 00000001 8068a3f1 b6e79c84
>     [10733.935496] 3fe0: 00000000 becfa7dc b6de194d b6e20246 400d0030 00000001 7a4536e8 49bda390
>     [10733.943664] [<c00653a0>] (do_raw_spin_lock) from [<c054c204>] (_raw_spin_lock+0x18/0x1c)
>     [10733.951743] [<c054c204>] (_raw_spin_lock) from [<c02fec60>] (fw_free_buf+0x24/0x64)
>     [10733.959388] [<c02fec60>] (fw_free_buf) from [<c02fed08>] (release_firmware+0x68/0x74)
>     [10733.967207] [<c02fed08>] (release_firmware) from [<c0253828>] (trigger_async_request_store+0x60/0x124)
>     [10733.976501] [<c0253828>] (trigger_async_request_store) from [<c02e873c>] (dev_attr_store+0x28/0x34)
>     [10733.985533] [<c02e873c>] (dev_attr_store) from [<c017bd40>] (sysfs_kf_write+0x4c/0x58)
>     [10733.993437] [<c017bd40>] (sysfs_kf_write) from [<c017b250>] (kernfs_fop_write+0x144/0x1a8)
>     [10734.001689] [<c017b250>] (kernfs_fop_write) from [<c011b71c>] (__vfs_write+0x3c/0xe4)
>
> After this patch:
>
>     # printf '\x00' > /sys/devices/virtual/misc/test_firmware/trigger_async_request
>     [   32.126322] test_firmware: loading ''
>     [   32.129995] test_firmware: failed to async load firmware
>     -bash: printf: write error: No such device
>
> Fixes: 471b095dfe0d ("firmware_class: make sure fw requests contain a name")
> Signed-off-by: Brian Norris <computersforpeace@xxxxxxxxx>

Good catch, thanks!

Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
>  drivers/base/firmware_class.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
> index 8524450e75bd..b9250e564ebf 100644
> --- a/drivers/base/firmware_class.c
> +++ b/drivers/base/firmware_class.c
> @@ -1118,15 +1118,17 @@ static int
>  _request_firmware(const struct firmware **firmware_p, const char *name,
>                   struct device *device, unsigned int opt_flags)
>  {
> -       struct firmware *fw;
> +       struct firmware *fw = NULL;
>         long timeout;
>         int ret;
>
>         if (!firmware_p)
>                 return -EINVAL;
>
> -       if (!name || name[0] == '\0')
> -               return -EINVAL;
> +       if (!name || name[0] == '\0') {
> +               ret = -EINVAL;
> +               goto out;
> +       }
>
>         ret = _request_firmware_prepare(&fw, name, device);
>         if (ret <= 0) /* error or already assigned */
> --
> 2.6.0.rc2.230.g3dd15c0
>



-- 
Kees Cook
Chrome OS & Brillo Security
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