[PATCH 1/6] firmware: permit LSMs and IMA to fail firmware sysfs fallback loading

On Fri, 2018-05-04 at 00:02 +0000, Luis R. Rodriguez wrote:

If you can add Andres Rodriguez [off-list ref], and Greg to your Cc list
in the future patches that'd be appreciated.

On Tue, May 01, 2018 at 09:48:18AM -0400, Mimi Zohar wrote:

quoted

Add an LSM hook prior to allowing firmware sysfs fallback loading.

Signed-off-by: Mimi Zohar <redacted>
Cc: Luis R. Rodriguez <redacted>
Cc: David Howells <dhowells@redhat.com>
Cc: Kees Cook <redacted>
Cc: Matthew Garrett <redacted>
---
 drivers/base/firmware_loader/fallback.c | 7 +++++++
 include/linux/fs.h                      | 1 +
 2 files changed, 8 insertions(+)

diff --git a/drivers/base/firmware_loader/fallback.c b/drivers/base/firmware_loader/fallback.c
index 31b5015b59fe..23d2af30474e 100644
--- a/drivers/base/firmware_loader/fallback.c
+++ b/drivers/base/firmware_loader/fallback.c

@@ -651,6 +651,8 @@ static bool fw_force_sysfs_fallback(unsigned int opt_flags)
 
 static bool fw_run_sysfs_fallback(unsigned int opt_flags)
 {
+	int ret;
+
 	if (fw_fallback_config.ignore_sysfs_fallback) {
 		pr_info_once("Ignoring firmware sysfs fallback due to sysctl knob\n");
 		return false;

@@ -659,6 +661,11 @@ static bool fw_run_sysfs_fallback(unsigned int opt_flags)
 	if ((opt_flags & FW_OPT_NOFALLBACK))
 		return false;
 
+	/* Also permit LSMs and IMA to fail firmware sysfs fallback */
+	ret = security_kernel_read_file(NULL, READING_FIRMWARE_FALLBACK);
+	if (ret < 0)
+		return ret;
+
 	return fw_force_sysfs_fallback(opt_flags);
 }
 

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 760d8da1b6c7..dc16a73c3d38 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h

@@ -2810,6 +2810,7 @@ extern int do_pipe_flags(int *, int);
 	id(UNKNOWN, unknown)		\
 	id(FIRMWARE, firmware)		\
 	id(FIRMWARE_PREALLOC_BUFFER, firmware)	\
+	id(FIRMWARE_FALLBACK, firmware)	\

If you're going to add this perhaps FIRMWARE_FALLBACK_SYSFS as we may later
get FIRMWARE_FALLBACK_EFI.

From an IMA signature verification perspective, both are buffer based.

?The file signature is stored as a security xattr. ?Without a file
descriptor, the kernel cannot verify the firmware signature.

I don't have a problem with defining another enumeration. ?Perhaps
other LSMs will want to be able to differentiate between sysfs and EFI
fallback methods.

Mimi

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