riscv: Fix memory leak in module_frob_arch_sections()

The current code directly overwrites the scratch pointer with the
return value of kvrealloc(). If kvrealloc() fails and returns NULL,
the original buffer becomes unreachable, causing a memory leak.

Fix this by using a temporary variable to store kvrealloc()'s return
value and only update the scratch pointer on success.

Found via static anlaysis and this is similar to commit 42378a9
("bpf, verifier: Fix memory leak in array reallocation for stack state")

Fixes: be17c0d ("riscv: module: Optimize PLT/GOT entry counting")
Cc: stable@vger.kernel.org
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Link: https://lore.kernel.org/r/20251026091912.39727-1-linmq006@gmail.com
Signed-off-by: Paul Walmsley <pjw@kernel.org>

Author: Yuuoniy

arch/riscv/kernel/module-sections.c

@@ -119,6 +119,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
 	unsigned int num_plts = 0;
 	unsigned int num_gots = 0;
 	Elf_Rela *scratch = NULL;
+	Elf_Rela *new_scratch;
 	size_t scratch_size = 0;
 	int i;
 
@@ -168,9 +169,12 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
 		scratch_size_needed = (num_scratch_relas + num_relas) * sizeof(*scratch);
 		if (scratch_size_needed > scratch_size) {
 			scratch_size = scratch_size_needed;
-			scratch = kvrealloc(scratch, scratch_size, GFP_KERNEL);
-			if (!scratch)
+			new_scratch = kvrealloc(scratch, scratch_size, GFP_KERNEL);
+			if (!new_scratch) {
+				kvfree(scratch);
 				return -ENOMEM;
+			}
+			scratch = new_scratch;
 		}
 
 		for (size_t j = 0; j < num_relas; j++)