fs/kernel_read_file: allow to read files up-to ssize_t

Patch series "Allow to kexec with initramfs larger than 2G", v2.

Currently, the largest initramfs that is supported by kexec_file_load()
syscall is 2G.

This is because kernel_read_file() returns int, and is limited to INT_MAX
or 2G.

On the other hand, there are kexec based boot loaders (i.e.  u-root), that
may need to boot netboot images that might be larger than 2G.

The first patch changes the return type from int to ssize_t in
kernel_read_file* functions.

The second patch increases the maximum initramfs file size to 4G.

Tested: verified that can kexec_file_load() works with 4G initramfs
on x86_64.


This patch (of 2):

Currently, the maximum file size that is supported is 2G.  This may be too
small in some cases.  For example, kexec_file_load() system call loads
initramfs.  In some netboot cases initramfs can be rather large.

Allow to use up-to ssize_t bytes.  The callers still can limit the maximum
file size via buf_size.

Link: https://lkml.kernel.org/r/20220527025535.3953665-1-pasha.tatashin@soleen.com
Link: https://lkml.kernel.org/r/20220527025535.3953665-2-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Baoquan He <bhe@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Sasha Levin <sashal@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 17 insertions, 16 deletions

diff --git a/include/linux/kernel_read_file.h b/include/linux/kernel_read_file.h
index 575ffa1031d3..90451e2e12bd 100644
--- a/include/linux/kernel_read_file.h
+++ b/include/linux/kernel_read_file.h
@@ -35,21 +35,21 @@ static inline const char *kernel_read_file_id_str(enum kernel_read_file_id id)
 	return kernel_read_file_str[id];
 }
 
-int kernel_read_file(struct file *file, loff_t offset,
-		     void **buf, size_t buf_size,
-		     size_t *file_size,
-		     enum kernel_read_file_id id);
-int kernel_read_file_from_path(const char *path, loff_t offset,
-			       void **buf, size_t buf_size,
-			       size_t *file_size,
-			       enum kernel_read_file_id id);
-int kernel_read_file_from_path_initns(const char *path, loff_t offset,
-				      void **buf, size_t buf_size,
-				      size_t *file_size,
-				      enum kernel_read_file_id id);
-int kernel_read_file_from_fd(int fd, loff_t offset,
-			     void **buf, size_t buf_size,
-			     size_t *file_size,
-			     enum kernel_read_file_id id);
+ssize_t kernel_read_file(struct file *file, loff_t offset,
+			 void **buf, size_t buf_size,
+			 size_t *file_size,
+			 enum kernel_read_file_id id);
+ssize_t kernel_read_file_from_path(const char *path, loff_t offset,
+				   void **buf, size_t buf_size,
+				   size_t *file_size,
+				   enum kernel_read_file_id id);
+ssize_t kernel_read_file_from_path_initns(const char *path, loff_t offset,
+					  void **buf, size_t buf_size,
+					  size_t *file_size,
+					  enum kernel_read_file_id id);
+ssize_t kernel_read_file_from_fd(int fd, loff_t offset,
+				 void **buf, size_t buf_size,
+				 size_t *file_size,
+				 enum kernel_read_file_id id);
 
 #endif /* _LINUX_KERNEL_READ_FILE_H */
diff --git a/include/linux/limits.h b/include/linux/limits.h
index b568b9c30bbf..f6bcc9369010 100644
--- a/include/linux/limits.h
+++ b/include/linux/limits.h
@@ -7,6 +7,7 @@
 #include <vdso/limits.h>
 
 #define SIZE_MAX	(~(size_t)0)
+#define SSIZE_MAX	((ssize_t)(SIZE_MAX >> 1))
 #define PHYS_ADDR_MAX	(~(phys_addr_t)0)
 
 #define U8_MAX		((u8)~0U)