linux-kernel - Re: [PATCH 1/7] binfmt: Move install_exec_creds after setup_new_exec to match binfmt

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Date:   Wed, 06 May 2020 07:56:59 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Greg Ungerer <gerg@...ux-m68k.org>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Rob Landley <rob@...dley.net>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        linux-fsdevel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/7] binfmt: Move install_exec_creds after setup_new_exec to match binfmt_elf

Greg Ungerer <gerg@...ux-m68k.org> writes:

> One small nit:

Good point.

> On 6/5/20 5:41 am, Eric W. Biederman wrote:
>> In 2016 Linus moved install_exec_creds immediately after
>> setup_new_exec, in binfmt_elf as a cleanup and as part of closing a
>> potential information leak.
>>
>> Perform the same cleanup for the other binary formats.
>>
>> Different binary formats doing the same things the same way makes exec
>> easier to reason about and easier to maintain.
>>
>> The binfmt_flagt bits were tested by Greg Ungerer <gerg@...ux-m68k.org>
>              ^^^^^
>              flat
>
> Regards
> Greg
>
>
>> Ref: 9f834ec18def ("binfmt_elf: switch to new creds when switching to new mm")
>> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
>> ---
>>   arch/x86/ia32/ia32_aout.c | 3 +--
>>   fs/binfmt_aout.c          | 2 +-
>>   fs/binfmt_elf_fdpic.c     | 2 +-
>>   fs/binfmt_flat.c          | 3 +--
>>   4 files changed, 4 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/x86/ia32/ia32_aout.c b/arch/x86/ia32/ia32_aout.c
>> index 9bb71abd66bd..37b36a8ce5fa 100644
>> --- a/arch/x86/ia32/ia32_aout.c
>> +++ b/arch/x86/ia32/ia32_aout.c
>> @@ -140,6 +140,7 @@ static int load_aout_binary(struct linux_binprm *bprm)
>>   	set_personality_ia32(false);
>>     	setup_new_exec(bprm);
>> +	install_exec_creds(bprm);
>>     	regs->cs = __USER32_CS;
>>   	regs->r8 = regs->r9 = regs->r10 = regs->r11 = regs->r12 =
>> @@ -156,8 +157,6 @@ static int load_aout_binary(struct linux_binprm *bprm)
>>   	if (retval < 0)
>>   		return retval;
>>   -	install_exec_creds(bprm);
>> -
>>   	if (N_MAGIC(ex) == OMAGIC) {
>>   		unsigned long text_addr, map_size;
>>   diff --git a/fs/binfmt_aout.c b/fs/binfmt_aout.c
>> index 8e8346a81723..ace587b66904 100644
>> --- a/fs/binfmt_aout.c
>> +++ b/fs/binfmt_aout.c
>> @@ -162,6 +162,7 @@ static int load_aout_binary(struct linux_binprm * bprm)
>>   	set_personality(PER_LINUX);
>>   #endif
>>   	setup_new_exec(bprm);
>> +	install_exec_creds(bprm);
>>     	current->mm->end_code = ex.a_text +
>>   		(current->mm->start_code = N_TXTADDR(ex));
>> @@ -174,7 +175,6 @@ static int load_aout_binary(struct linux_binprm * bprm)
>>   	if (retval < 0)
>>   		return retval;
>>   -	install_exec_creds(bprm);
>>     	if (N_MAGIC(ex) == OMAGIC) {
>>   		unsigned long text_addr, map_size;
>> diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
>> index 240f66663543..6c94c6d53d97 100644
>> --- a/fs/binfmt_elf_fdpic.c
>> +++ b/fs/binfmt_elf_fdpic.c
>> @@ -353,6 +353,7 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm)
>>   		current->personality |= READ_IMPLIES_EXEC;
>>     	setup_new_exec(bprm);
>> +	install_exec_creds(bprm);
>>     	set_binfmt(&elf_fdpic_format);
>>   @@ -434,7 +435,6 @@ static int load_elf_fdpic_binary(struct linux_binprm
>> *bprm)
>>   	current->mm->start_stack = current->mm->start_brk + stack_size;
>>   #endif
>>   -	install_exec_creds(bprm);
>>   	if (create_elf_fdpic_tables(bprm, current->mm,
>>   				    &exec_params, &interp_params) < 0)
>>   		goto error;
>> diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
>> index 831a2b25ba79..1a1d1fcb893f 100644
>> --- a/fs/binfmt_flat.c
>> +++ b/fs/binfmt_flat.c
>> @@ -541,6 +541,7 @@ static int load_flat_file(struct linux_binprm *bprm,
>>   		/* OK, This is the point of no return */
>>   		set_personality(PER_LINUX_32BIT);
>>   		setup_new_exec(bprm);
>> +		install_exec_creds(bprm);
>>   	}
>>     	/*
>> @@ -963,8 +964,6 @@ static int load_flat_binary(struct linux_binprm *bprm)
>>   		}
>>   	}
>>   -	install_exec_creds(bprm);
>> -
>>   	set_binfmt(&flat_format);
>>     #ifdef CONFIG_MMU
>>