Re: [PATCH v2 0/5] Fix ELF / FDPIC ELF core dumping, and use mmap_sem properly in there

Greg Ungerer [off-list ref] writes:

On 1/5/20 5:07 am, Eric W. Biederman wrote:

quoted

Linus Torvalds [off-list ref] writes:

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On Thu, Apr 30, 2020 at 7:10 AM Greg Ungerer [off-list ref] wrote:

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Most of that file goes back to pre-git days. And most of the commits
since are not so much about binfmt_flat, as they are about cleanups or
changes elsewhere where binfmt_flat was just a victim.

I'll have a look at this.

Thanks.

quoted

Quick hack test shows moving setup_new_exec(bprm) to be just before
install_exec_creds(bprm) works fine for the static binaries case.
Doing the flush_old_exec(bprm) there too crashed out - I'll need to
dig into that to see why.

Just moving setup_new_exec() would at least allow us to then join the
two together, and just say "setup_new_exec() does the credential
installation too".

But it is only half a help if we allow failure points between
flush_old_exec and install_exec_creds.

Greg do things work acceptably if install_exec_creds is moved to right
after setup_new_exec? (patch below)

Yes, confirmed. Worked fine with that patch applied.

Good.  Thank you.

That is what we need for other cleanups.  All three of those together.

quoted

This is what I was thinking about applying.

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

Eric

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