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.bran...@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 306fc566171e..751f5ddc7538 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -927,10 +927,15 @@ 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;
 
@@ -950,21 +955,31 @@ 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;
@@ -972,14 +987,16 @@ 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;
 
@@ -995,10 +1012,20 @@ 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;
@@ -1010,15 +1037,24 @@ 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)
+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;
@@ -1036,14 +1072,24 @@ 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;
@@ -1051,11 +1097,18 @@ 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 db604c7bd79c..aee7600958ef 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

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