[PATCH 1/3] fs: introduce kernel_pread_file* support

[Scott Branden]

Add kernel_pread_file* support to kernel to allow for partial read
of files with an offset into the file.  Existing kernel_read_file
functions call new kernel_pread_file functions with offset=0 and
flags=KERNEL_PREAD_FLAG_WHOLE.

Signed-off-by: Scott Branden <scott.branden@xxxxxxxxxxxx>
---
 fs/exec.c          | 77 ++++++++++++++++++++++++++++++++++++----------
 include/linux/fs.h | 15 +++++++++
 2 files changed, 75 insertions(+), 17 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index d88584ebf07f..ba56450acfb3 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -892,10 +892,14 @@ struct file *open_exec(const char *name)
 }
 EXPORT_SYMBOL(open_exec);
 
-int kernel_read_file(struct file *file, void **buf, loff_t *size,
-		     loff_t max_size, enum kernel_read_file_id id)
-{
-	loff_t i_size, pos;
+int kernel_pread_file(struct file *file, void **buf, loff_t *size,
+		      loff_t pos, loff_t max_size, unsigned int flags,
+		      enum kernel_read_file_id id)
+{
+	loff_t alloc_size;
+	loff_t buf_pos;
+	loff_t read_end;
+	loff_t i_size;
 	ssize_t bytes = 0;
 	int ret;
 
@@ -915,21 +919,31 @@ 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)) {
+
+	/* Default read to end of file */
+	read_end = i_size;
+
+	/* Allow reading partial portion of file */
+	if ((flags & KERNEL_PREAD_FLAG_PART) &&
+	    (i_size > (pos + max_size)))
+		read_end = pos + max_size;
+
+	alloc_size = read_end - pos;
+	if (i_size > SIZE_MAX || (max_size > 0 && alloc_size > max_size)) {
 		ret = -EFBIG;
 		goto out;
 	}
 
 	if (id != READING_FIRMWARE_PREALLOC_BUFFER)
-		*buf = vmalloc(i_size);
+		*buf = vmalloc(alloc_size);
 	if (!*buf) {
 		ret = -ENOMEM;
 		goto out;
 	}
 
-	pos = 0;
-	while (pos < i_size) {
-		bytes = kernel_read(file, *buf + pos, i_size - pos, &pos);
+	buf_pos = 0;
+	while (pos < read_end) {
+		bytes = kernel_read(file, *buf + buf_pos, read_end - pos, &pos);
 		if (bytes < 0) {
 			ret = bytes;
 			goto out_free;
@@ -937,14 +951,16 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
 
 		if (bytes == 0)
 			break;
+
+		buf_pos += bytes;
 	}
 
-	if (pos != i_size) {
+	if (pos != read_end) {
 		ret = -EIO;
 		goto out_free;
 	}
 
-	ret = security_kernel_post_read_file(file, *buf, i_size, id);
+	ret = security_kernel_post_read_file(file, *buf, alloc_size, id);
 	if (!ret)
 		*size = pos;
 
@@ -960,10 +976,20 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
 	allow_write_access(file);
 	return ret;
 }
+EXPORT_SYMBOL_GPL(kernel_pread_file);
+
+int kernel_read_file(struct file *file, void **buf, loff_t *size,
+		     loff_t max_size, enum kernel_read_file_id id)
+{
+	return kernel_pread_file(file, buf, size, 0, max_size,
+				 KERNEL_PREAD_FLAG_WHOLE, id);
+}
 EXPORT_SYMBOL_GPL(kernel_read_file);
 
-int kernel_read_file_from_path(const char *path, void **buf, loff_t *size,
-			       loff_t max_size, enum kernel_read_file_id id)
+int kernel_pread_file_from_path(const char *path, void **buf,
+				loff_t *size, loff_t pos,
+				loff_t max_size, unsigned int flags,
+				enum kernel_read_file_id id)
 {
 	struct file *file;
 	int ret;
@@ -975,14 +1001,23 @@ 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_pread_file(file, buf, size, pos, max_size, flags, id);
 	fput(file);
 	return ret;
 }
+EXPORT_SYMBOL_GPL(kernel_pread_file_from_path);
+
+int kernel_read_file_from_path(const char *path, void **buf, loff_t *size,
+			       loff_t max_size, enum kernel_read_file_id id)
+{
+	return kernel_pread_file_from_path(path, buf, size, 0, max_size,
+					   KERNEL_PREAD_FLAG_WHOLE, id);
+}
 EXPORT_SYMBOL_GPL(kernel_read_file_from_path);
 
-int kernel_read_file_from_fd(int fd, void **buf, loff_t *size, loff_t max_size,
-			     enum kernel_read_file_id id)
+int kernel_pread_file_from_fd(int fd, void **buf, loff_t *size, loff_t pos,
+			      loff_t max_size, unsigned int flags,
+			      enum kernel_read_file_id id)
 {
 	struct fd f = fdget(fd);
 	int ret = -EBADF;
@@ -990,11 +1025,19 @@ 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_pread_file(f.file, buf, size, pos, max_size, flags, id);
 out:
 	fdput(f);
 	return ret;
 }
+EXPORT_SYMBOL_GPL(kernel_pread_file_from_fd);
+
+int kernel_read_file_from_fd(int fd, void **buf, loff_t *size, loff_t max_size,
+			     enum kernel_read_file_id id)
+{
+	return kernel_pread_file_from_fd(fd, buf, size, 0, max_size,
+					 KERNEL_PREAD_FLAG_WHOLE, id);
+}
 EXPORT_SYMBOL_GPL(kernel_read_file_from_fd);
 
 ssize_t read_code(struct file *file, unsigned long addr, loff_t pos, size_t len)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f7fdfe93e25d..033a3e7f0015 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2942,10 +2942,25 @@ static inline const char *kernel_read_file_id_str(enum kernel_read_file_id id)
 	return kernel_read_file_str[id];
 }
 
+/* Flags used by kernel_pread_file functions */
+#define KERNEL_PREAD_FLAG_WHOLE	0x0000 /* Only Allow reading of whole file */
+#define KERNEL_PREAD_FLAG_PART	0x0001 /* Allow reading part of file */
+
+extern int kernel_pread_file(struct file *file, void **buf, loff_t *size,
+			     loff_t pos, loff_t max_size, unsigned int flags,
+			     enum kernel_read_file_id id);
 extern int kernel_read_file(struct file *, void **, loff_t *, loff_t,
 			    enum kernel_read_file_id);
+extern int kernel_pread_file_from_path(const char *path, void **buf,
+				       loff_t *size, loff_t pos,
+				       loff_t max_size, unsigned int flags,
+				       enum kernel_read_file_id id);
 extern int kernel_read_file_from_path(const char *, void **, loff_t *, loff_t,
 				      enum kernel_read_file_id);
+extern int kernel_pread_file_from_fd(int fd, void **buf, loff_t *size,
+				    loff_t pos, loff_t max_size,
+				    unsigned int flags,
+				    enum kernel_read_file_id id);
 extern int kernel_read_file_from_fd(int, void **, loff_t *, loff_t,
 				    enum kernel_read_file_id);
 extern ssize_t kernel_read(struct file *, void *, size_t, loff_t *);
-- 
2.17.1