2019-06-17 18:25:51

by Sven Van Asbroeck

Subject: [PATCH] firmware: improve LSM/IMA security behaviour

The firmware loader queries if LSM/IMA permits it to load firmware
via the sysfs fallback. Unfortunately, the code does the opposite:
it expressly permits sysfs fw loading if security_kernel_load_data(
LOADING_FIRMWARE) returns -EACCES. This happens because a
zero-on-success return value is cast to a bool that's true on success.

Fix the return value handling so we get the correct behaviour.

Fixes: 6e852651f28e ("firmware: add call to LSM hook before firmware sysfs fallback")
Cc: Stable <[email protected]>
Cc: Mimi Zohar <[email protected]>
Cc: Kees Cook <[email protected]>
To: Luis Chamberlain <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: [email protected]
Signed-off-by: Sven Van Asbroeck <[email protected]>
---
drivers/base/firmware_loader/fallback.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/firmware_loader/fallback.c b/drivers/base/firmware_loader/fallback.c
index f962488546b6..103b5d37fa86 100644
--- a/drivers/base/firmware_loader/fallback.c
+++ b/drivers/base/firmware_loader/fallback.c
@@ -659,7 +659,7 @@ static bool fw_run_sysfs_fallback(enum fw_opt opt_flags)
/* Also permit LSMs and IMA to fail firmware sysfs fallback */
ret = security_kernel_load_data(LOADING_FIRMWARE);
if (ret < 0)
- return ret;
+ return false;

return fw_force_sysfs_fallback(opt_flags);
}
--
2.17.1

2019-06-17 18:34:52

by Mimi Zohar

Subject: Re: [PATCH] firmware: improve LSM/IMA security behaviour

On Mon, 2019-06-17 at 14:23 -0400, Sven Van Asbroeck wrote:
> The firmware loader queries if LSM/IMA permits it to load firmware
> via the sysfs fallback. Unfortunately, the code does the opposite:
> it expressly permits sysfs fw loading if security_kernel_load_data(
> LOADING_FIRMWARE) returns -EACCES. This happens because a
> zero-on-success return value is cast to a bool that's true on success.
>
> Fix the return value handling so we get the correct behaviour.

Reviewed-by: Mimi Zohar <[email protected]>