Re: [PATCH 02/13] fs/kernel_read_file: Remove FIRMWARE_PREALLOC_BUFFER enum

Scott Branden <scott.branden@xxxxxxxxxxxx> · Fri, 17 Jul 2020 12:09:10 -0700

On 2020-07-17 10:42 a.m., Kees Cook wrote:
FIRMWARE_PREALLOC_BUFFER is a "how", not a "what", and confuses the LSMs
that are interested in filtering between types of things. The "how"
should be an internal detail made uninteresting to the LSMs.

Fixes: a098ecd2fa7d ("firmware: support loading into a pre-allocated buffer")
Fixes: fd90bc559bfb ("ima: based on policy verify firmware signatures (pre-allocated buffer)")
Fixes: 4f0496d8ffa3 ("ima: based on policy warn about loading firmware (pre-allocated buffer)")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Scott Branden <scott.branden@xxxxxxxxxxxx>
---
To aid in backporting, this change is made before moving
kernel_read_file() to separate header/source files.
---
  drivers/base/firmware_loader/main.c | 5 ++---
  fs/exec.c                           | 7 ++++---
  include/linux/fs.h                  | 2 +-
  kernel/module.c                     | 2 +-
  security/integrity/digsig.c         | 2 +-
  security/integrity/ima/ima_fs.c     | 2 +-
  security/integrity/ima/ima_main.c   | 6 ++----
  7 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
index ca871b13524e..c2f57cedcd6f 100644
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -465,14 +465,12 @@ fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv,
  	int i, len;
  	int rc = -ENOENT;
  	char *path;
-	enum kernel_read_file_id id = READING_FIRMWARE;
  	size_t msize = INT_MAX;
  	void *buffer = NULL;
  
  	/* Already populated data member means we're loading into a buffer */
  	if (!decompress && fw_priv->data) {
  		buffer = fw_priv->data;
-		id = READING_FIRMWARE_PREALLOC_BUFFER;
  		msize = fw_priv->allocated_size;
  	}
  
@@ -496,7 +494,8 @@ fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv,
  
  		/* load firmware files from the mount namespace of init */
  		rc = kernel_read_file_from_path_initns(path, &buffer,
-						       &size, msize, id);
+						       &size, msize,
+						       READING_FIRMWARE);
  		if (rc) {
  			if (rc != -ENOENT)
  				dev_warn(device, "loading %s failed with error %d\n",
diff --git a/fs/exec.c b/fs/exec.c
index e6e8a9a70327..2bf549757ce7 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -927,6 +927,7 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
  {
  	loff_t i_size, pos;
  	ssize_t bytes = 0;
+	void *allocated = NULL;
  	int ret;
  
  	if (!S_ISREG(file_inode(file)->i_mode) || max_size < 0)
@@ -950,8 +951,8 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
  		goto out;
  	}
  
-	if (id != READING_FIRMWARE_PREALLOC_BUFFER)
-		*buf = vmalloc(i_size);
+	if (!*buf)
+		*buf = allocated = vmalloc(i_size);
  	if (!*buf) {
  		ret = -ENOMEM;
  		goto out;
@@ -980,7 +981,7 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
  
  out_free:
  	if (ret < 0) {
-		if (id != READING_FIRMWARE_PREALLOC_BUFFER) {
+		if (allocated) {
  			vfree(*buf);
  			*buf = NULL;
  		}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3f881a892ea7..95fc775ed937 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2993,10 +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*. */
  #define __kernel_read_file_id(id) \
  	id(UNKNOWN, unknown)		\
  	id(FIRMWARE, firmware)		\
-	id(FIRMWARE_PREALLOC_BUFFER, firmware)	\
  	id(FIRMWARE_EFI_EMBEDDED, firmware)	\
  	id(MODULE, kernel-module)		\
  	id(KEXEC_IMAGE, kexec-image)		\
diff --git a/kernel/module.c b/kernel/module.c
index 0c6573b98c36..26105148f4d2 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3988,7 +3988,7 @@ SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags)
  {
  	struct load_info info = { };
  	loff_t size;
-	void *hdr;
+	void *hdr = NULL;
  	int err;
  
  	err = may_init_module();
diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
index e9cbadade74b..ac02b7632353 100644
--- a/security/integrity/digsig.c
+++ b/security/integrity/digsig.c
@@ -169,7 +169,7 @@ int __init integrity_add_key(const unsigned int id, const void *data,
  
  int __init integrity_load_x509(const unsigned int id, const char *path)
  {
-	void *data;
+	void *data = NULL;
  	loff_t size;
  	int rc;
  	key_perm_t perm;
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index e3fcad871861..15a44c5022f7 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -272,7 +272,7 @@ static const struct file_operations ima_ascii_measurements_ops = {
  
  static ssize_t ima_read_policy(char *path)
  {
-	void *data;
+	void *data = NULL;
  	char *datap;
  	loff_t size;
  	int rc, pathlen = strlen(path);
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index c1583d98c5e5..f80ee4ce4669 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -611,19 +611,17 @@ void ima_post_path_mknod(struct dentry *dentry)
  int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
  {
  	/*
-	 * READING_FIRMWARE_PREALLOC_BUFFER
-	 *
  	 * Do devices using pre-allocated memory run the risk of the
  	 * firmware being accessible to the device prior to the completion
  	 * of IMA's signature verification any more than when using two
-	 * buffers?
+	 * buffers? It may be desirable to include the buffer address
+	 * in this API and walk all the dma_map_single() mappings to check.
  	 */
  	return 0;
  }
  
  const int read_idmap[READING_MAX_ID] = {
  	[READING_FIRMWARE] = FIRMWARE_CHECK,
-	[READING_FIRMWARE_PREALLOC_BUFFER] = FIRMWARE_CHECK,
  	[READING_MODULE] = MODULE_CHECK,
  	[READING_KEXEC_IMAGE] = KEXEC_KERNEL_CHECK,
  	[READING_KEXEC_INITRAMFS] = KEXEC_INITRAMFS_CHECK,







