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

[Yunqiang Su]

Ping...

We really need it. since qemu-user mode have no other choice to get the info about whether P flag is set.

> -----Original Message-----
> From: Laurent Vivier <laurent@xxxxxxxxx>
> Sent: 2019å12æ16æ 17:22
> To: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx; Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>;
> James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>; Yunqiang Su
> <ysu@xxxxxxxxxxxx>
> Subject: [EXTERNAL]Re: [RFC v2] binfmt_misc: pass binfmt_misc flags to the
> interpreter
> 
> Hi,
> 
> this feature is really needed and requested by several binfmt_misc users. It is
> difficult to manage this at user level without this information.
> 
> I've found that someone else tried to address this problem in the past in the
> same way:
> https://patchwork.kernel.org/patch/10902935/
> 
> Can a maintainer/reviewer have a look at this and agrees or disagrees?
> 
> I will update getauxval(3) manual page with the new flags in the case one of
> these patches is 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. */
> >
> >