Re: [PATCH 06/13] fs/kernel_read_file: Remove redundant size argument

Scott Branden <scott.branden@xxxxxxxxxxxx> · Fri, 17 Jul 2020 12:04:18 -0700

Hi Kees,

On 2020-07-17 10:43 a.m., Kees Cook wrote:
In preparation for refactoring kernel_read_file*(), remove the redundant
"size" argument which is not needed: it can be included in the return
I don't think the size argument is redundant though.
The existing kernel_read_file functions always read the whole file.
Now, what happens if the file is bigger than the buffer.
How does kernel_read_file know it read the whole file by looking at the 
return value?
code, with callers adjusted. (VFS reads already cannot be larger than
INT_MAX.)

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
  drivers/base/firmware_loader/main.c |  8 ++++----
  fs/kernel_read_file.c               | 20 +++++++++-----------
  include/linux/kernel_read_file.h    |  8 ++++----
  kernel/kexec_file.c                 | 13 ++++++-------
  kernel/module.c                     |  7 +++----
  security/integrity/digsig.c         |  5 +++--
  security/integrity/ima/ima_fs.c     |  5 +++--
  7 files changed, 32 insertions(+), 34 deletions(-)

diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
index d4a413ea48ce..ea419c7d3d34 100644
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -462,7 +462,7 @@ fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv,
  					     size_t in_size,
  					     const void *in_buffer))
  {
-	loff_t size;
+	size_t size;
  	int i, len;
  	int rc = -ENOENT;
  	char *path;
@@ -494,10 +494,9 @@ fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv,
  		fw_priv->size = 0;
  
  		/* load firmware files from the mount namespace of init */
-		rc = kernel_read_file_from_path_initns(path, &buffer,
-						       &size, msize,
+		rc = kernel_read_file_from_path_initns(path, &buffer, msize,
  						       READING_FIRMWARE);
-		if (rc) {
+		if (rc < 0) {
  			if (rc != -ENOENT)
  				dev_warn(device, "loading %s failed with error %d\n",
  					 path, rc);
@@ -506,6 +505,7 @@ fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv,
  					 path);
  			continue;
  		}
+		size = rc;
  		dev_dbg(device, "Loading firmware from %s\n", path);
  		if (decompress) {
  			dev_dbg(device, "f/w decompressing %s\n",
diff --git a/fs/kernel_read_file.c b/fs/kernel_read_file.c
index 54d972d4befc..dc28a8def597 100644
--- a/fs/kernel_read_file.c
+++ b/fs/kernel_read_file.c
@@ -5,7 +5,7 @@
  #include <linux/security.h>
  #include <linux/vmalloc.h>
  
-int kernel_read_file(struct file *file, void **buf, loff_t *size,
+int kernel_read_file(struct file *file, void **buf,
  		     loff_t max_size, enum kernel_read_file_id id)
  {
  	loff_t i_size, pos;
@@ -29,7 +29,7 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
  		ret = -EINVAL;
  		goto out;
  	}
-	if (i_size > SIZE_MAX || (max_size > 0 && i_size > max_size)) {
+	if (i_size > INT_MAX || (max_size > 0 && i_size > max_size)) {
Should this be SSIZE_MAX?
  		ret = -EFBIG;
  		goto out;
  	}
@@ -59,8 +59,6 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
  	}
  
  	ret = security_kernel_post_read_file(file, *buf, i_size, id);
-	if (!ret)
-		*size = pos;
  
  out_free:
  	if (ret < 0) {
@@ -72,11 +70,11 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
  
  out:
  	allow_write_access(file);
-	return ret;
+	return ret == 0 ? pos : ret;
  }
  EXPORT_SYMBOL_GPL(kernel_read_file);
  
-int kernel_read_file_from_path(const char *path, void **buf, loff_t *size,
+int kernel_read_file_from_path(const char *path, void **buf,
  			       loff_t max_size, enum kernel_read_file_id id)
  {
  	struct file *file;
@@ -89,14 +87,14 @@ int kernel_read_file_from_path(const char *path, void **buf, loff_t *size,
  	if (IS_ERR(file))
  		return PTR_ERR(file);
  
-	ret = kernel_read_file(file, buf, size, max_size, id);
+	ret = kernel_read_file(file, buf, max_size, id);
  	fput(file);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(kernel_read_file_from_path);
  
  int kernel_read_file_from_path_initns(const char *path, void **buf,
-				      loff_t *size, loff_t max_size,
+				      loff_t max_size,
  				      enum kernel_read_file_id id)
  {
  	struct file *file;
@@ -115,13 +113,13 @@ int kernel_read_file_from_path_initns(const char *path, void **buf,
  	if (IS_ERR(file))
  		return PTR_ERR(file);
  
-	ret = kernel_read_file(file, buf, size, max_size, id);
+	ret = kernel_read_file(file, buf, max_size, id);
  	fput(file);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(kernel_read_file_from_path_initns);
  
-int kernel_read_file_from_fd(int fd, void **buf, loff_t *size, loff_t max_size,
+int kernel_read_file_from_fd(int fd, void **buf, loff_t max_size,
  			     enum kernel_read_file_id id)
  {
  	struct fd f = fdget(fd);
@@ -130,7 +128,7 @@ int kernel_read_file_from_fd(int fd, void **buf, loff_t *size, loff_t max_size,
  	if (!f.file)
  		goto out;
  
-	ret = kernel_read_file(f.file, buf, size, max_size, id);
+	ret = kernel_read_file(f.file, buf, max_size, id);
  out:
  	fdput(f);
  	return ret;
diff --git a/include/linux/kernel_read_file.h b/include/linux/kernel_read_file.h
index 78cf3d7dc835..0ca0bdbed1bd 100644
--- a/include/linux/kernel_read_file.h
+++ b/include/linux/kernel_read_file.h
@@ -36,16 +36,16 @@ static inline const char *kernel_read_file_id_str(enum kernel_read_file_id id)
  }
  
  int kernel_read_file(struct file *file,
-		     void **buf, loff_t *size, loff_t max_size,
+		     void **buf, loff_t max_size,
  		     enum kernel_read_file_id id);
  int kernel_read_file_from_path(const char *path,
-			       void **buf, loff_t *size, loff_t max_size,
+			       void **buf, loff_t max_size,
  			       enum kernel_read_file_id id);
  int kernel_read_file_from_path_initns(const char *path,
-				      void **buf, loff_t *size, loff_t max_size,
+				      void **buf, loff_t max_size,
  				      enum kernel_read_file_id id);
  int kernel_read_file_from_fd(int fd,
-			     void **buf, loff_t *size, loff_t max_size,
+			     void **buf, loff_t max_size,
  			     enum kernel_read_file_id id);
  
  #endif /* _LINUX_KERNEL_READ_FILE_H */
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 1358069ce9e9..a201bbb19158 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -220,13 +220,12 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
  {
  	int ret;
  	void *ldata;
-	loff_t size;
  
  	ret = kernel_read_file_from_fd(kernel_fd, &image->kernel_buf,
-				       &size, INT_MAX, READING_KEXEC_IMAGE);
-	if (ret)
+				       INT_MAX, READING_KEXEC_IMAGE);
+	if (ret < 0)
  		return ret;
-	image->kernel_buf_len = size;
+	image->kernel_buf_len = ret;
  
  	/* Call arch image probe handlers */
  	ret = arch_kexec_kernel_image_probe(image, image->kernel_buf,
@@ -243,11 +242,11 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
  	/* It is possible that there no initramfs is being loaded */
  	if (!(flags & KEXEC_FILE_NO_INITRAMFS)) {
  		ret = kernel_read_file_from_fd(initrd_fd, &image->initrd_buf,
-					       &size, INT_MAX,
+					       INT_MAX,
  					       READING_KEXEC_INITRAMFS);
-		if (ret)
+		if (ret < 0)
  			goto out;
-		image->initrd_buf_len = size;
+		image->initrd_buf_len = ret;
  	}
  
  	if (cmdline_len) {
diff --git a/kernel/module.c b/kernel/module.c
index e9765803601b..b6fd4f51cc30 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3988,7 +3988,6 @@ SYSCALL_DEFINE3(init_module, void __user *, umod,
  SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags)
  {
  	struct load_info info = { };
-	loff_t size;
  	void *hdr = NULL;
  	int err;
  
@@ -4002,12 +4001,12 @@ SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags)
  		      |MODULE_INIT_IGNORE_VERMAGIC))
  		return -EINVAL;
  
-	err = kernel_read_file_from_fd(fd, &hdr, &size, INT_MAX,
+	err = kernel_read_file_from_fd(fd, &hdr, INT_MAX,
  				       READING_MODULE);
-	if (err)
+	if (err < 0)
  		return err;
  	info.hdr = hdr;
-	info.len = size;
+	info.len = err;
  
  	return load_module(&info, uargs, flags);
  }
diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
index f8869be45d8f..97661ffabc4e 100644
--- a/security/integrity/digsig.c
+++ b/security/integrity/digsig.c
@@ -171,16 +171,17 @@ 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 = NULL;
-	loff_t size;
+	size_t size;
  	int rc;
  	key_perm_t perm;
  
-	rc = kernel_read_file_from_path(path, &data, &size, 0,
+	rc = kernel_read_file_from_path(path, &data, 0,
  					READING_X509_CERTIFICATE);
  	if (rc < 0) {
  		pr_err("Unable to open file: %s (%d)", path, rc);
  		return rc;
  	}
+	size = rc;
  
  	perm = (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_VIEW | KEY_USR_READ;
  
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index e13ffece3726..9ba145d3d6d9 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -275,7 +275,7 @@ static ssize_t ima_read_policy(char *path)
  {
  	void *data = NULL;
  	char *datap;
-	loff_t size;
+	size_t size;
  	int rc, pathlen = strlen(path);
  
  	char *p;
@@ -284,11 +284,12 @@ static ssize_t ima_read_policy(char *path)
  	datap = path;
  	strsep(&datap, "\n");
  
-	rc = kernel_read_file_from_path(path, &data, &size, 0, READING_POLICY);
+	rc = kernel_read_file_from_path(path, &data, 0, READING_POLICY);
  	if (rc < 0) {
  		pr_err("Unable to open file: %s (%d)", path, rc);
  		return rc;
  	}
+	size = rc;
  
  	datap = data;
  	while (size > 0 && (p = strsep(&datap, "\n"))) {







