[PATCH v6 1/8] fs: introduce kernel_pread_file* support

Scott Branden
2020-06-05T23:00:17Z

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
opt=KERNEL_PREAD_WHOLE.

Signed-off-by: Scott Branden <scott.branden@broadcom.com>
---
fs/exec.c | 95 ++++++++++++++++++++++++++++++++++++----------
include/linux/fs.h | 29 ++++++++++++++
2 files changed, 103 insertions(+), 21 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index de90a66587ab..e5c241c07b75 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -925,10 +925,15 @@ 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,
+ enum kernel_pread_opt opt,
+ 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;

@@ -948,21 +953,31 @@ 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 ((opt == KERNEL_PREAD_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;
@@ -970,14 +985,16 @@ 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;

@@ -993,10 +1010,20 @@ 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, 0, max_size,
+ KERNEL_PREAD_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,
+ enum kernel_pread_opt opt,
+ enum kernel_read_file_id id)
{
struct file *file;
int ret;
@@ -1008,15 +1035,24 @@ 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, opt, 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, 0, max_size,
+ KERNEL_PREAD_WHOLE, 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)
+extern int kernel_pread_file_from_path_initns(const char *path, void **buf,
+ loff_t *size, loff_t pos,
+ loff_t max_size,
+ enum kernel_pread_opt opt,
+ enum kernel_read_file_id id)
{
struct file *file;
struct path root;
@@ -1034,14 +1070,24 @@ 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, pos, max_size, opt, 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, 0, max_size,
+ KERNEL_PREAD_WHOLE, 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 pos,
+ loff_t max_size,
+ enum kernel_pread_opt opt,
+ enum kernel_read_file_id id)
{
struct fd f = fdget(fd);
int ret = -EBADF;
@@ -1049,11 +1095,18 @@ 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, opt, 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, 0, max_size,
+ KERNEL_PREAD_WHOLE, 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 fce4b8867224..76d463e4a628 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3048,12 +3048,41 @@ static inline const char *kernel_read_file_id_str(enum kernel_read_file_id id)
return kernel_read_file_str[id];
}

+/**
+ * enum kernel_pread_opt - options to control pread file loading behaviour
+ *
+ * @KERNEL_PREAD_WHOLE: Only Allow reading of whole file.
+ * @KERNEL_PREAD_PART: Allow reading part of file.
+ */
+enum kernel_pread_opt {
+ KERNEL_PREAD_WHOLE = 0,
+ KERNEL_PREAD_PART = BIT(0),
+};
+
+int kernel_pread_file(struct file *file, void **buf, loff_t *size,
+ loff_t pos, loff_t max_size,
+ enum kernel_pread_opt opt,
+ 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_pread_opt opt,
+ 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_pread_opt opt,
+ 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_pread_opt opt,
+ 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