[PATCH v9 1/8] fs: introduce kernel_pread_file* support

15 Jun 2020

Add kernel_pread_file* support to kernel to allow for partial read
of files with an offset into the file.
Signed-off-by: Scott Branden scott.branden@broadcom.com
---
 fs/exec.c          | 93 ++++++++++++++++++++++++++++++++++------------
 include/linux/fs.h | 15 ++++++++
 2 files changed, 85 insertions(+), 23 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 7b7cbb180785..c557b4b31d0f 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -927,10 +927,14 @@ 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 max_size, loff_t pos,
+		      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;
@@ -950,21 +954,32 @@ 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 ((id == READING_FIRMWARE_PARTIAL_READ) &&
+	    (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);
+	if ((id != READING_FIRMWARE_PARTIAL_READ) &&
+	    (id != READING_FIRMWARE_PREALLOC_BUFFER))
+		*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;
@@ -972,20 +987,23 @@ 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;
out_free:
    if (ret < 0) {
-		if (id != READING_FIRMWARE_PREALLOC_BUFFER) {
+		if ((id != READING_FIRMWARE_PARTIAL_READ) &&
+		    (id != READING_FIRMWARE_PREALLOC_BUFFER)) {
    		vfree(*buf);
    		*buf = NULL;
    	}
@@ -995,10 +1013,18 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
    allow_write_access(file);
    return ret;
 }
+
+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, max_size, 0, 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 max_size, loff_t pos,
+				enum kernel_read_file_id id)
 {
    struct file *file;
    int ret;
@@ -1010,15 +1036,22 @@ 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, max_size, pos, id);
    fput(file);
    return ret;
 }
+
+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, max_size, 0, id);
+}
 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,
-				      enum kernel_read_file_id id)
+int kernel_pread_file_from_path_initns(const char *path, void **buf,
+				       loff_t *size,
+				       loff_t max_size, loff_t pos,
+				       enum kernel_read_file_id id)
 {
    struct file *file;
    struct path root;
@@ -1036,14 +1069,22 @@ 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_pread_file(file, buf, size, max_size, pos, id);
    fput(file);
    return ret;
 }
+
+int kernel_read_file_from_path_initns(const char *path, void **buf,
+				      loff_t *size, loff_t max_size,
+				      enum kernel_read_file_id id)
+{
+	return kernel_pread_file_from_path_initns(path, buf, size, max_size, 0, id);
+}
 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,
-			     enum kernel_read_file_id id)
+int kernel_pread_file_from_fd(int fd, void **buf, loff_t *size,
+			      loff_t max_size, loff_t pos,
+			      enum kernel_read_file_id id)
 {
    struct fd f = fdget(fd);
    int ret = -EBADF;
@@ -1051,11 +1092,17 @@ 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, max_size, pos, id);
 out:
    fdput(f);
    return ret;
 }
+
+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, max_size, 0, id);
+}
 EXPORT_SYMBOL_GPL(kernel_read_file_from_fd);
#if defined(CONFIG_HAVE_AOUT) || defined(CONFIG_BINFMT_FLAT) || \
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6931c469040b..3ac1d213577a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3012,6 +3012,7 @@ extern int do_pipe_flags(int *, int);
 #define __kernel_read_file_id(id) \
    id(UNKNOWN, unknown)		\
    id(FIRMWARE, firmware)		\
+	id(FIRMWARE_PARTIAL_READ, firmware)	\
    id(FIRMWARE_PREALLOC_BUFFER, firmware)	\
    id(FIRMWARE_EFI_EMBEDDED, firmware)	\
    id(MODULE, kernel-module)		\
@@ -3040,12 +3041,26 @@ static inline const char *kernel_read_file_id_str(enum kernel_read_file_id id)
    return kernel_read_file_str[id];
 }
+int kernel_pread_file(struct file *file, void **buf, loff_t *size,
+		      loff_t pos, loff_t max_size,
+		      enum kernel_read_file_id id);
 extern int kernel_read_file(struct file *, void **, loff_t *, loff_t,
    		    enum kernel_read_file_id);
+int kernel_pread_file_from_path(const char *path, void **buf,
+				loff_t *size, loff_t pos,
+				loff_t max_size,
+				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);
+int kernel_pread_file_from_path_initns(const char *path, void **buf,
+				       loff_t *size, loff_t pos,
+				       loff_t max_size,
+				       enum kernel_read_file_id id);
 extern int kernel_read_file_from_path_initns(const char *, void **, loff_t *, loff_t,
    				     enum kernel_read_file_id);
+int kernel_pread_file_from_fd(int fd, void **buf, loff_t *size,
+			      loff_t pos, loff_t max_size,
+			      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


    

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[PATCH v9 1/8] fs: introduce kernel_pread_file* support