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

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

[Colin King]

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

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

[Nicholas Piggin]

Excerpts from Colin King's message of March 19, 2021 1:59 am:
> 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>

Looks good to me.

Acked-by: Nicholas Piggin <npiggin@gmail.com>

Thanks,
Nick

> ---
>  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
> 
>