fs: binfmt_elf_efpic: don't use missing interpreter's properties

[PATCH] fs: binfmt_elf_efpic: don't use missing interpreter's properties

Posted by Max Filippov 1 year, 11 months ago

Static FDPIC executable may get an executable stack even when it has
non-executable GNU_STACK segment. This happens when STACK segment has rw
permissions, but does not specify stack size. In that case FDPIC loader
uses permissions of the interpreter's stack, and for static executables
with no interpreter it results in choosing the arch-default permissions
for the stack.

Fix that by using the interpreter's properties only when the interpreter
is actually used.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
 fs/binfmt_elf_fdpic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index be4e7ac3efbc..f6d72fe3998c 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -322,7 +322,7 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm)
 	else
 		executable_stack = EXSTACK_DEFAULT;
 
-	if (stack_size == 0) {
+	if (stack_size == 0 && interp_params.flags & ELF_FDPIC_FLAG_PRESENT) {
 		stack_size = interp_params.stack_size;
 		if (interp_params.flags & ELF_FDPIC_FLAG_EXEC_STACK)
 			executable_stack = EXSTACK_ENABLE_X;
-- 
2.39.2

Re: [PATCH] fs: binfmt_elf_efpic: don't use missing interpreter's properties

Posted by Kees Cook 1 year, 10 months ago

On Thu, 18 Jan 2024 07:06:37 -0800, Max Filippov wrote:
> Static FDPIC executable may get an executable stack even when it has
> non-executable GNU_STACK segment. This happens when STACK segment has rw
> permissions, but does not specify stack size. In that case FDPIC loader
> uses permissions of the interpreter's stack, and for static executables
> with no interpreter it results in choosing the arch-default permissions
> for the stack.
> 
> [...]

Applied to for-next/execve, thanks!

[1/1] fs: binfmt_elf_efpic: don't use missing interpreter's properties
      https://git.kernel.org/kees/c/15fd1dc3dadb

Take care,

-- 
Kees Cook

Re: [PATCH] fs: binfmt_elf_efpic: don't use missing interpreter's properties

Posted by Max Filippov 1 year, 10 months ago

Ping?

On Thu, Jan 18, 2024 at 7:07 AM Max Filippov <jcmvbkbc@gmail.com> wrote:
>
> Static FDPIC executable may get an executable stack even when it has
> non-executable GNU_STACK segment. This happens when STACK segment has rw
> permissions, but does not specify stack size. In that case FDPIC loader
> uses permissions of the interpreter's stack, and for static executables
> with no interpreter it results in choosing the arch-default permissions
> for the stack.
>
> Fix that by using the interpreter's properties only when the interpreter
> is actually used.
>
> Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
> ---
>  fs/binfmt_elf_fdpic.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
> index be4e7ac3efbc..f6d72fe3998c 100644
> --- a/fs/binfmt_elf_fdpic.c
> +++ b/fs/binfmt_elf_fdpic.c
> @@ -322,7 +322,7 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm)
>         else
>                 executable_stack = EXSTACK_DEFAULT;
>
> -       if (stack_size == 0) {
> +       if (stack_size == 0 && interp_params.flags & ELF_FDPIC_FLAG_PRESENT) {
>                 stack_size = interp_params.stack_size;
>                 if (interp_params.flags & ELF_FDPIC_FLAG_EXEC_STACK)
>                         executable_stack = EXSTACK_ENABLE_X;
> --
> 2.39.2
>


-- 
Thanks.
-- Max