[v2,7/8] binfmt_elf: don't attempt to load FDPIC binaries

[Vincent ABRIOU]

Hi Nicolas,

On 08/17/2017 09:23 AM, Nicolas Pitre wrote:
> On platforms where both ELF and ELF-FDPIC variants are available, the
> regular ELF loader will happily identify FDPIC binaries as proper ELF
> and load them without the necessary FDPIC fixups, resulting in an
> immediate user space crash. Let's prevent binflt_elf from loading those
> binaries so binfmt_elf_fdpic has a chance to pick them up. For those
> architectures that don't define elf_check_fdpic(), a default version
> returning false is provided.
> 
> Signed-off-by: Nicolas Pitre <nico at linaro.org>
Tested-by: Vincent Abriou <vincent.abriou at st.com>

BR
Vincent

> ---
>   fs/binfmt_elf.c | 15 +++++++++++++--
>   1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 879ff9c7ff..84d64afaea 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -51,6 +51,11 @@
>   #define user_siginfo_t siginfo_t
>   #endif
>   
> +/* That's for binfmt_elf_fdpic to deal with */
> +#ifndef elf_check_fdpic
> +#define elf_check_fdpic(ex) false
> +#endif
> +
>   static int load_elf_binary(struct linux_binprm *bprm);
>   static unsigned long elf_map(struct file *, unsigned long, struct elf_phdr *,
>   				int, int, unsigned long);
> @@ -541,7 +546,8 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
>   	if (interp_elf_ex->e_type != ET_EXEC &&
>   	    interp_elf_ex->e_type != ET_DYN)
>   		goto out;
> -	if (!elf_check_arch(interp_elf_ex))
> +	if (!elf_check_arch(interp_elf_ex) ||
> +	    elf_check_fdpic(interp_elf_ex))
>   		goto out;
>   	if (!interpreter->f_op->mmap)
>   		goto out;
> @@ -718,6 +724,8 @@ static int load_elf_binary(struct linux_binprm *bprm)
>   		goto out;
>   	if (!elf_check_arch(&loc->elf_ex))
>   		goto out;
> +	if (elf_check_fdpic(&loc->elf_ex))
> +		goto out;
>   	if (!bprm->file->f_op->mmap)
>   		goto out;
>   
> @@ -817,7 +825,8 @@ static int load_elf_binary(struct linux_binprm *bprm)
>   		if (memcmp(loc->interp_elf_ex.e_ident, ELFMAG, SELFMAG) != 0)
>   			goto out_free_dentry;
>   		/* Verify the interpreter has a valid arch */
> -		if (!elf_check_arch(&loc->interp_elf_ex))
> +		if (!elf_check_arch(&loc->interp_elf_ex) ||
> +		    elf_check_fdpic(&loc->interp_elf_ex))
>   			goto out_free_dentry;
>   
>   		/* Load the interpreter program headers */
> @@ -1189,6 +1198,8 @@ static int load_elf_library(struct file *file)
>   	if (elf_ex.e_type != ET_EXEC || elf_ex.e_phnum > 2 ||
>   	    !elf_check_arch(&elf_ex) || !file->f_op->mmap)
>   		goto out;
> +	if (elf_check_fdpic(&elf_ex))
> +		goto out;
>   
>   	/* Now read in all of the header information */
>   
>