Re: [PATCH 1/5] MIPS: Bail on unsupported module relocs

[James Hogan]

On Wed, Feb 03, 2016 at 03:44:41AM +0000, Paul Burton wrote:
> When an unsupported reloc is encountered in a module, we currently
> blindly branch to whatever would be at its entry in the reloc handler
> function pointer arrays. This may be NULL, or if the unsupported reloc
> has a type greater than that of the supported reloc with the highest
> type then we'll dereference some value after the function pointer array
> & branch to that. The result is at best a kernel oops.
> 
> Fix this by checking that the reloc type has an entry in the function
> pointer array (ie. is less than the number of items in the array) and
> that the handler is non-NULL, returning an error code to fail the module
> load if no handler is found.
> 
> Signed-off-by: Paul Burton <paul.burton@xxxxxxxxxx>
> Cc: James Hogan <james.hogan@xxxxxxxxxx>

Reviewed-by: James Hogan <james.hogan@xxxxxxxxxx>

Cheers
James

> ---
> 
>  arch/mips/kernel/module-rela.c | 19 ++++++++++++++++---
>  arch/mips/kernel/module.c      | 19 ++++++++++++++++---
>  2 files changed, 32 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/mips/kernel/module-rela.c b/arch/mips/kernel/module-rela.c
> index 2b70723..769e316 100644
> --- a/arch/mips/kernel/module-rela.c
> +++ b/arch/mips/kernel/module-rela.c
> @@ -109,9 +109,10 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
>  		       struct module *me)
>  {
>  	Elf_Mips_Rela *rel = (void *) sechdrs[relsec].sh_addr;
> +	int (*handler)(struct module *me, u32 *location, Elf_Addr v);
>  	Elf_Sym *sym;
>  	u32 *location;
> -	unsigned int i;
> +	unsigned int i, type;
>  	Elf_Addr v;
>  	int res;
>  
> @@ -134,9 +135,21 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
>  			return -ENOENT;
>  		}
>  
> -		v = sym->st_value + rel[i].r_addend;
> +		type = ELF_MIPS_R_TYPE(rel[i]);
> +
> +		if (type < ARRAY_SIZE(reloc_handlers_rela))
> +			handler = reloc_handlers_rela[type];
> +		else
> +			handler = NULL;
>  
> -		res = reloc_handlers_rela[ELF_MIPS_R_TYPE(rel[i])](me, location, v);
> +		if (!handler) {
> +			pr_warn("%s: Unknown relocation type %u\n",
> +				me->name, type);
> +			return -EINVAL;
> +		}
> +
> +		v = sym->st_value + rel[i].r_addend;
> +		res = handler(me, location, v);
>  		if (res)
>  			return res;
>  	}
> diff --git a/arch/mips/kernel/module.c b/arch/mips/kernel/module.c
> index 1833f51..2adf572 100644
> --- a/arch/mips/kernel/module.c
> +++ b/arch/mips/kernel/module.c
> @@ -197,9 +197,10 @@ int apply_relocate(Elf_Shdr *sechdrs, const char *strtab,
>  		   struct module *me)
>  {
>  	Elf_Mips_Rel *rel = (void *) sechdrs[relsec].sh_addr;
> +	int (*handler)(struct module *me, u32 *location, Elf_Addr v);
>  	Elf_Sym *sym;
>  	u32 *location;
> -	unsigned int i;
> +	unsigned int i, type;
>  	Elf_Addr v;
>  	int res;
>  
> @@ -223,9 +224,21 @@ int apply_relocate(Elf_Shdr *sechdrs, const char *strtab,
>  			return -ENOENT;
>  		}
>  
> -		v = sym->st_value;
> +		type = ELF_MIPS_R_TYPE(rel[i]);
> +
> +		if (type < ARRAY_SIZE(reloc_handlers_rel))
> +			handler = reloc_handlers_rel[type];
> +		else
> +			handler = NULL;
>  
> -		res = reloc_handlers_rel[ELF_MIPS_R_TYPE(rel[i])](me, location, v);
> +		if (!handler) {
> +			pr_warn("%s: Unknown relocation type %u\n",
> +				me->name, type);
> +			return -EINVAL;
> +		}
> +
> +		v = sym->st_value;
> +		res = handler(me, location, v);
>  		if (res)
>  			return res;
>  	}
> -- 
> 2.7.0
>

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