kernel: kexec_file: fix error return code of kexec_calculate_store_digests()

When vzalloc() returns NULL to sha_regions, no error return code of
kexec_calculate_store_digests() is assigned.  To fix this bug, ret is
assigned with -ENOMEM in this case.

Link: https://lkml.kernel.org/r/20210309083904.24321-1-baijiaju1990@gmail.com
Fixes: a43cac0d ("kexec: split kexec_file syscall code to kexec_file.c")
Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
Acked-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/kexec_file.c

@@ -740,8 +740,10 @@ static int kexec_calculate_store_digests(struct kimage *image)
 
 	sha_region_sz = KEXEC_SEGMENT_MAX * sizeof(struct kexec_sha_region);
 	sha_regions = vzalloc(sha_region_sz);
-	if (!sha_regions)
+	if (!sha_regions) {
+		ret = -ENOMEM;
 		goto out_free_desc;
+	}
 
 	desc->tfm   = tfm;