Re: [RFC v2] binfmt_misc: pass binfmt_misc flags to the interpreter

[Laurent Vivier]

Hi,

this change is simple, easy to read and understand but it is really
needed by user space application interpreter to know the status of the
system configuration.

Could we have a comment saying if there is a problem or if it is good to
be merged?

Thanks,
Laurent

Le 22/11/2019 Ã 16:08, Laurent Vivier a ÃcritÂ:
> It can be useful to the interpreter to know which flags are in use.
> 
> For instance, knowing if the preserve-argv[0] is in use would
> allow to skip the pathname argument.
> 
> This patch uses an unused auxiliary vector, AT_FLAGS,  to pass the
> content of the binfmt flags (special flags: P, F, C, O).
> 
> Signed-off-by: Laurent Vivier <laurent@xxxxxxxxx>
> ---
> 
> Notes:
>     v2: only pass special flags (remove Magic and Enabled flags)
> 
>  fs/binfmt_elf.c         | 2 +-
>  fs/binfmt_elf_fdpic.c   | 2 +-
>  fs/binfmt_misc.c        | 6 ++++++
>  include/linux/binfmts.h | 2 +-
>  4 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index c5642bcb6b46..7a34c03e5857 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -250,7 +250,7 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
>  	NEW_AUX_ENT(AT_PHENT, sizeof(struct elf_phdr));
>  	NEW_AUX_ENT(AT_PHNUM, exec->e_phnum);
>  	NEW_AUX_ENT(AT_BASE, interp_load_addr);
> -	NEW_AUX_ENT(AT_FLAGS, 0);
> +	NEW_AUX_ENT(AT_FLAGS, bprm->fmt_flags);
>  	NEW_AUX_ENT(AT_ENTRY, exec->e_entry);
>  	NEW_AUX_ENT(AT_UID, from_kuid_munged(cred->user_ns, cred->uid));
>  	NEW_AUX_ENT(AT_EUID, from_kuid_munged(cred->user_ns, cred->euid));
> diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
> index d86ebd0dcc3d..8fe839be125e 100644
> --- a/fs/binfmt_elf_fdpic.c
> +++ b/fs/binfmt_elf_fdpic.c
> @@ -647,7 +647,7 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
>  	NEW_AUX_ENT(AT_PHENT,	sizeof(struct elf_phdr));
>  	NEW_AUX_ENT(AT_PHNUM,	exec_params->hdr.e_phnum);
>  	NEW_AUX_ENT(AT_BASE,	interp_params->elfhdr_addr);
> -	NEW_AUX_ENT(AT_FLAGS,	0);
> +	NEW_AUX_ENT(AT_FLAGS,	bprm->fmt_flags);
>  	NEW_AUX_ENT(AT_ENTRY,	exec_params->entry_addr);
>  	NEW_AUX_ENT(AT_UID,	(elf_addr_t) from_kuid_munged(cred->user_ns, cred->uid));
>  	NEW_AUX_ENT(AT_EUID,	(elf_addr_t) from_kuid_munged(cred->user_ns, cred->euid));
> diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
> index cdb45829354d..25a392f23409 100644
> --- a/fs/binfmt_misc.c
> +++ b/fs/binfmt_misc.c
> @@ -48,6 +48,9 @@ enum {Enabled, Magic};
>  #define MISC_FMT_OPEN_BINARY (1 << 30)
>  #define MISC_FMT_CREDENTIALS (1 << 29)
>  #define MISC_FMT_OPEN_FILE (1 << 28)
> +#define MISC_FMT_FLAGS_MASK (MISC_FMT_PRESERVE_ARGV0 | MISC_FMT_OPEN_BINARY | \
> +			     MISC_FMT_CREDENTIALS | MISC_FMT_OPEN_FILE)
> +
>  
>  typedef struct {
>  	struct list_head list;
> @@ -149,6 +152,9 @@ static int load_misc_binary(struct linux_binprm *bprm)
>  	if (!fmt)
>  		return retval;
>  
> +	/* pass special flags to the interpreter */
> +	bprm->fmt_flags = fmt->flags & MISC_FMT_FLAGS_MASK;
> +
>  	/* Need to be able to load the file after exec */
>  	retval = -ENOENT;
>  	if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
> diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
> index b40fc633f3be..dae0d0d7b84d 100644
> --- a/include/linux/binfmts.h
> +++ b/include/linux/binfmts.h
> @@ -60,7 +60,7 @@ struct linux_binprm {
>  				   different for binfmt_{misc,script} */
>  	unsigned interp_flags;
>  	unsigned interp_data;
> -	unsigned long loader, exec;
> +	unsigned long loader, exec, fmt_flags;
>  
>  	struct rlimit rlim_stack; /* Saved RLIMIT_STACK used during exec. */
>  
>