[PATCH 3/4] fs: Remove FIRMWARE_EFI_EMBEDDED from kernel_read_file() enums

Kees Cook
2020-07-07T08:19:55Z

The "FIRMWARE_EFI_EMBEDDED" enum is a "where", not a "what". It
should not be distinguished separately from just "FIRMWARE", as this
confuses the LSMs about what is being loaded. Additionally, there was
no actual validation of the firmware contents happening. Add call to
security_kernel_post_read_file() so the contents can be measured/verified,
just as the firmware sysfs fallback does. This would allow for IMA (or
other LSMs) to validate known-good EFI firmware images.

Fixes: e4c2c0ff00ec ("firmware: Add new platform fallback mechanism and firmware_request_platform()")
Signed-off-by: Kees Cook <keescook@chromium.org>
---
drivers/base/firmware_loader/fallback_platform.c | 7 ++++++-
include/linux/fs.h | 3 +--
include/linux/lsm_hooks.h | 6 +++++-
3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/base/firmware_loader/fallback_platform.c b/drivers/base/firmware_loader/fallback_platform.c
index 685edb7dd05a..76e0c4a7835f 100644
--- a/drivers/base/firmware_loader/fallback_platform.c
+++ b/drivers/base/firmware_loader/fallback_platform.c
@@ -17,7 +17,7 @@ int firmware_fallback_platform(struct fw_priv *fw_priv, u32 opt_flags)
if (!(opt_flags & FW_OPT_FALLBACK_PLATFORM))
return -ENOENT;

- rc = security_kernel_load_data(LOADING_FIRMWARE_EFI_EMBEDDED);
+ rc = security_kernel_load_data(LOADING_FIRMWARE);
if (rc)
return rc;

@@ -25,6 +25,11 @@ int firmware_fallback_platform(struct fw_priv *fw_priv, u32 opt_flags)
if (rc)
return rc; /* rc == -ENOENT when the fw was not found */

+ rc = security_kernel_post_read_file(NULL, (char *)data, size,
+ READING_FIRMWARE);
+ if (rc)
+ return rc;
+
if (fw_priv->data && size > fw_priv->allocated_size)
return -ENOMEM;
if (!fw_priv->data)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 95fc775ed937..f50a35d54a61 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2993,11 +2993,10 @@ static inline void i_readcount_inc(struct inode *inode)
#endif
extern int do_pipe_flags(int *, int);

-/* This is a list of *what* is being read, not *how*. */
+/* This is a list of *what* is being read, not *how* nor *where*. */
#define __kernel_read_file_id(id) \
id(UNKNOWN, unknown) \
id(FIRMWARE, firmware) \
- id(FIRMWARE_EFI_EMBEDDED, firmware) \
id(MODULE, kernel-module) \
id(KEXEC_IMAGE, kexec-image) \
id(KEXEC_INITRAMFS, kexec-initramfs) \
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 95b7c1d32062..7cfc3166a1e2 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -633,15 +633,19 @@
* @kmod_name name of the module requested by the kernel
* Return 0 if successful.
* @kernel_load_data:
- * Load data provided by userspace.
+ * Load data provided by a non-file source (usually userspace buffer).
* @id kernel load data identifier
* Return 0 if permission is granted.
+ * This may be paired with a kernel_post_read_file() with a NULL
+ * @file, but contains the actual data loaded.
* @kernel_read_file:
* Read a file specified by userspace.
* @file contains the file structure pointing to the file being read
* by the kernel.
* @id kernel read file identifier
* Return 0 if permission is granted.
+ * This must be paired with a kernel_post_read_file(), which contains
+ * the actual data read from @file.
* @kernel_post_read_file:
* Read a file specified by userspace.
* @file contains the file structure pointing to the file being read
--
2.25.1