[PATCH v10 2/9] fs: introduce kernel_pread_file* support

From: Scott Branden
Date: Mon Jul 06 2020 - 19:23:47 EST

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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@xxxxxxxxxxxx>
---
fs/exec.c | 93 ++++++++++++++++++++++++--------
include/linux/kernel_read_file.h | 17 ++++++
2 files changed, 87 insertions(+), 23 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 4ea87db5e4d5..e6a8a65f7478 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -928,10 +928,14 @@ 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;

@@ -951,21 +955,32 @@ 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;
@@ -973,20 +988,23 @@ 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;
}
@@ -996,10 +1014,18 @@ 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;
@@ -1011,15 +1037,22 @@ 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;
@@ -1037,14 +1070,22 @@ 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;
@@ -1052,11 +1093,17 @@ 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/kernel_read_file.h b/include/linux/kernel_read_file.h
index 53f5ca41519a..f061ccb8d0b4 100644
--- a/include/linux/kernel_read_file.h
+++ b/include/linux/kernel_read_file.h
@@ -8,6 +8,7 @@
#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) \
@@ -36,15 +37,31 @@ 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);
int kernel_read_file(struct file *file,
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_read_file_id id);
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_initns(const char *path,
+ void **buf, loff_t *size, loff_t pos,
+ 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,
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_read_file_id id);
int kernel_read_file_from_fd(int fd,
void **buf, loff_t *size, loff_t max_size,
enum kernel_read_file_id id);
--
2.17.1

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