Re: [PATCH v2 09/18] fs/kernel_read_file: Switch buffer size arg to size_t

Scott Branden <scott.branden@xxxxxxxxxxxx> · Thu, 23 Jul 2020 10:36:11 -0700

works.

On 2020-07-22 12:30 p.m., Kees Cook wrote:
In preparation for further refactoring of kernel_read_file*(), rename
the "max_size" argument to the more accurate "buf_size", and correct
its type to size_t. Add kerndoc to explain the specifics of how the
arguments will be used. Note that with buf_size now size_t, it can no
longer be negative (and was never called with a negative value). Adjust
callers to use it as a "maximum size" when *buf is NULL.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Scott Branden <scott.branden@xxxxxxxxxxxx>
---
  fs/kernel_read_file.c            | 34 +++++++++++++++++++++++---------
  include/linux/kernel_read_file.h |  8 ++++----
  security/integrity/digsig.c      |  2 +-
  security/integrity/ima/ima_fs.c  |  2 +-
  4 files changed, 31 insertions(+), 15 deletions(-)

diff --git a/fs/kernel_read_file.c b/fs/kernel_read_file.c
index dc28a8def597..e21a76001fff 100644
--- a/fs/kernel_read_file.c
+++ b/fs/kernel_read_file.c
@@ -5,15 +5,31 @@
  #include <linux/security.h>
  #include <linux/vmalloc.h>
  
+/**
+ * kernel_read_file() - read file contents into a kernel buffer
+ *
+ * @file	file to read from
+ * @buf		pointer to a "void *" buffer for reading into (if
+ *		*@buf is NULL, a buffer will be allocated, and
+ *		@buf_size will be ignored)
+ * @buf_size	size of buf, if already allocated. If @buf not
+ *		allocated, this is the largest size to allocate.
+ * @id		the kernel_read_file_id identifying the type of
+ *		file contents being read (for LSMs to examine)
+ *
+ * Returns number of bytes read (no single read will be bigger
+ * than INT_MAX), or negative on error.
+ *
+ */
  int kernel_read_file(struct file *file, void **buf,
-		     loff_t max_size, enum kernel_read_file_id id)
+		     size_t buf_size, enum kernel_read_file_id id)
  {
  	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)
+	if (!S_ISREG(file_inode(file)->i_mode))
  		return -EINVAL;
  
  	ret = deny_write_access(file);
@@ -29,7 +45,7 @@ int kernel_read_file(struct file *file, void **buf,
  		ret = -EINVAL;
  		goto out;
  	}
-	if (i_size > INT_MAX || (max_size > 0 && i_size > max_size)) {
+	if (i_size > INT_MAX || i_size > buf_size) {
  		ret = -EFBIG;
  		goto out;
  	}
@@ -75,7 +91,7 @@ int kernel_read_file(struct file *file, void **buf,
  EXPORT_SYMBOL_GPL(kernel_read_file);
  
  int kernel_read_file_from_path(const char *path, void **buf,
-			       loff_t max_size, enum kernel_read_file_id id)
+			       size_t buf_size, enum kernel_read_file_id id)
  {
  	struct file *file;
  	int ret;
@@ -87,14 +103,14 @@ int kernel_read_file_from_path(const char *path, void **buf,
  	if (IS_ERR(file))
  		return PTR_ERR(file);
  
-	ret = kernel_read_file(file, buf, max_size, id);
+	ret = kernel_read_file(file, buf, buf_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 max_size,
+				      size_t buf_size,
  				      enum kernel_read_file_id id)
  {
  	struct file *file;
@@ -113,13 +129,13 @@ 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, max_size, id);
+	ret = kernel_read_file(file, buf, buf_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 max_size,
+int kernel_read_file_from_fd(int fd, void **buf, size_t buf_size,
  			     enum kernel_read_file_id id)
  {
  	struct fd f = fdget(fd);
@@ -128,7 +144,7 @@ int kernel_read_file_from_fd(int fd, void **buf, loff_t max_size,
  	if (!f.file)
  		goto out;
  
-	ret = kernel_read_file(f.file, buf, max_size, id);
+	ret = kernel_read_file(f.file, buf, buf_size, id);
  out:
  	fdput(f);
  	return ret;
diff --git a/include/linux/kernel_read_file.h b/include/linux/kernel_read_file.h
index 0ca0bdbed1bd..910039e7593e 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 max_size,
+		     void **buf, size_t buf_size,
  		     enum kernel_read_file_id id);
  int kernel_read_file_from_path(const char *path,
-			       void **buf, loff_t max_size,
+			       void **buf, size_t buf_size,
  			       enum kernel_read_file_id id);
  int kernel_read_file_from_path_initns(const char *path,
-				      void **buf, loff_t max_size,
+				      void **buf, size_t buf_size,
  				      enum kernel_read_file_id id);
  int kernel_read_file_from_fd(int fd,
-			     void **buf, loff_t max_size,
+			     void **buf, size_t buf_size,
  			     enum kernel_read_file_id id);
  
  #endif /* _LINUX_KERNEL_READ_FILE_H */
diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
index 97661ffabc4e..04f779c4f5ed 100644
--- a/security/integrity/digsig.c
+++ b/security/integrity/digsig.c
@@ -175,7 +175,7 @@ int __init integrity_load_x509(const unsigned int id, const char *path)
  	int rc;
  	key_perm_t perm;
  
-	rc = kernel_read_file_from_path(path, &data, 0,
+	rc = kernel_read_file_from_path(path, &data, INT_MAX,
  					READING_X509_CERTIFICATE);
  	if (rc < 0) {
  		pr_err("Unable to open file: %s (%d)", path, rc);
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 602f52717757..692b83e82edf 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -284,7 +284,7 @@ static ssize_t ima_read_policy(char *path)
  	datap = path;
  	strsep(&datap, "\n");
  
-	rc = kernel_read_file_from_path(path, &data, 0, READING_POLICY);
+	rc = kernel_read_file_from_path(path, &data, INT_MAX, READING_POLICY);
  	if (rc < 0) {
  		pr_err("Unable to open file: %s (%d)", path, rc);
  		return rc;


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