[PATCH][next] mm/vmalloc: fix read of uninitialized pointer area

From: Colin King <colin.king@canonical.com>
To: Andrew Morton <akpm@linux-foundation.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Nicholas Piggin <npiggin@gmail.com>,
	linux-mm@kvack.org
Cc: kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH][next] mm/vmalloc: fix read of uninitialized pointer area
Date: Thu, 18 Mar 2021 15:59:55 +0000	[thread overview]
Message-ID: <20210318155955.18220-1-colin.king@canonical.com> (raw)

From: Colin Ian King <colin.king@canonical.com>

There is a corner case where the sanity check of variable size fails
and branches to label fail and shift can be less than PAGE_SHIFT
causing area to never be assigned. This was picked up by static
analysis as follows:

    1. var_decl: Declaring variable area without initializer.
       struct vm_struct *area;

   ...

    2. Condition !size, taking true branch.
       if (!size || (size >> PAGE_SHIFT) > totalram_pages())
    3. Jumping to label fail.
               goto fail;

    ...

    4. Condition shift > 12, taking false branch.
	fail:
		if (shift > PAGE_SHIFT) {
			shift = PAGE_SHIFT;
			align = real_align;
			size = real_size;
			goto again;
		}

     Uninitialized pointer read (UNINIT)
     5. uninit_use: Using uninitialized value area.
 		if (!area) {
			...
		}

Fix this by setting area to NULL to avoid the uninitialized read
of area.

Addresses-Coverity: ("Uninitialized pointer read")
Fixes: 92db9fec381b ("mm/vmalloc: hugepage vmalloc mappings")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 mm/vmalloc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 96444d64129a..4b415b4bb7ae 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2888,8 +2888,10 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 	unsigned long real_align = align;
 	unsigned int shift = PAGE_SHIFT;
 
-	if (!size || (size >> PAGE_SHIFT) > totalram_pages())
+	if (!size || (size >> PAGE_SHIFT) > totalram_pages()) {
+		area = NULL;
 		goto fail;
+	}
 
 	if (vmap_allow_huge && !(vm_flags & VM_NO_HUGE_VMAP) &&
 			arch_vmap_pmd_supported(prot)) {
-- 
2.30.2

