linux-kernel - Re: [RFC v2] binfmt_misc: pass binfmt

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Date:   Wed, 15 Jan 2020 13:19:16 +0100
From:   Laurent Vivier <laurent@...ier.eu>
To:     linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     linux-fsdevel@...r.kernel.org,
        James Bottomley <James.Bottomley@...senPartnership.com>
Subject: Re: [RFC v2] binfmt_misc: pass binfmt_misc flags to the interpreter

Le 07/01/2020 à 15:50, Laurent Vivier a écrit :
> 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?

Anyone?

> Thanks,
> Laurent
> 
> Le 22/11/2019 à 16:08, Laurent Vivier a écrit :
>> 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@...ier.eu>
>> ---
>>
>> 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. */
>>  
>>
>