module: decompress: check return value of module_extend_max_pages()

commit 786d2d8441 upstream.

module_extend_max_pages() calls kvrealloc() internally and returns
-ENOMEM on allocation failure. The return value is never checked.

If the initial allocation fails, info->pages remains NULL and
info->max_pages remains 0. Subsequent calls to module_get_next_page()
will attempt to dynamically grow the array by calling
module_extend_max_pages(info, 0) since info->used_pages is 0. This
results in kvrealloc(NULL, 0) returning ZERO_SIZE_PTR, which is treated
as a success, leading to a dereference of ZERO_SIZE_PTR and a kernel
oops.

Fix: add the missing error check after module_extend_max_pages() and
return immediately on failure. This matches the pattern used by every
other kvrealloc() caller in the module loading path.

Fixes: b1ae6dc41e ("module: add in-kernel support for decompressing")
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Andrii Kuchmenko <capyenglishlite@gmail.com>
Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
[Sami: Corrected the analysis in the commit message.]
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

kernel/module/decompress.c

@@ -307,6 +307,8 @@ int module_decompress(struct load_info *info, const void *buf, size_t size)
 	 */
 	n_pages = DIV_ROUND_UP(size, PAGE_SIZE) * 2;
 	error = module_extend_max_pages(info, n_pages);
+	if (error)
+		return error;
 
 	data_size = MODULE_DECOMPRESS_FN(info, buf, size);
 	if (data_size < 0) {