module/decompress: use vmalloc() for gzip decompression workspace

Use a similar approach as commit a419beac ("module/decompress: use
vmalloc() for zstd decompression workspace") and replace kmalloc() with
vmalloc() also for the gzip module decompression workspace.

In this case the workspace is represented by struct inflate_workspace
that can be fairly large for kmalloc() and it can potentially lead to
allocation errors on certain systems:

$ pahole inflate_workspace
struct inflate_workspace {
	struct inflate_state       inflate_state;        /*     0  9544 */
	/* --- cacheline 149 boundary (9536 bytes) was 8 bytes ago --- */
	unsigned char              working_window[32768]; /*  9544 32768 */

	/* size: 42312, cachelines: 662, members: 2 */
	/* last cacheline: 8 bytes */
};

Considering that there is no need to use continuous physical memory,
simply switch to vmalloc() to provide a more reliable in-kernel module
decompression.

Fixes: b1ae6dc4 ("module: add in-kernel support for decompressing")
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

kernel/module/decompress.c

@@ -100,7 +100,7 @@ static ssize_t module_gzip_decompress(struct load_info *info,
 	s.next_in = buf + gzip_hdr_len;
 	s.avail_in = size - gzip_hdr_len;
 
-	s.workspace = kmalloc(zlib_inflate_workspacesize(), GFP_KERNEL);
+	s.workspace = vmalloc(zlib_inflate_workspacesize());
 	if (!s.workspace)
 		return -ENOMEM;
 
@@ -138,7 +138,7 @@ static ssize_t module_gzip_decompress(struct load_info *info,
 out_inflate_end:
 	zlib_inflateEnd(&s);
 out:
-	kfree(s.workspace);
+	vfree(s.workspace);
 	return retval;
 }
 #elif defined(CONFIG_MODULE_COMPRESS_XZ)