'struct dynamic': struct tag leak in UAPI headers

* 'struct dynamic': struct tag leak in UAPI headers
@ 2023-08-29 12:08 Alejandro Colomar
  2023-08-29 12:24 ` Matthew Wilcox
       [not found] ` <20230829185121.326228-1-alx@kernel.org>
  0 siblings, 2 replies; 10+ messages in thread
From: Alejandro Colomar @ 2023-08-29 12:08 UTC (permalink / raw)
  To: David Howells, Eric Biederman, Kees Cook, linux-mm, Rolf Eike Beer
  Cc: Arnd Bergmann, Thomas Gleixner, Paul E. McKenney, Dave Jones

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Hi!

I was reading elf(7), and while checking the actual type definitions
on my system, I found out a kernel struct tag that probably shouldn't
be there.

Here's the definition of 'Elf64_Dyn' in my <linux/elf.h>.

$ grepc Elf64_Dyn /usr/include/linux/elf.h 
/usr/include/linux/elf.h:151:
typedef struct {
  Elf64_Sxword d_tag;		/* entry tag value */
  union {
    Elf64_Xword d_val;
    Elf64_Addr d_ptr;
  } d_un;
} Elf64_Dyn;

And here's the one for 'Elf32_Dyn'.  Notice that here there's a
struct tag.  I expect that such a tag would be prefixed by ElfN_,
but it isn't.

$ grepc Elf32_Dyn /usr/include/linux/elf.h 
/usr/include/linux/elf.h:143:
typedef struct dynamic {
  Elf32_Sword d_tag;
  union {
    Elf32_Sword	d_val;
    Elf32_Addr	d_ptr;
  } d_un;
} Elf32_Dyn;

It seems we should blame an automated script :)

$ git blame -- ./include/uapi/linux/elf.h | grep 'struct dynamic';
23a7aea5faf65 (Rolf Eike Beer        2022-10-04 12:25:40 +0200 143) typedef struct dynamic {

$ git blame 23a7aea5faf65^ -- ./include/uapi/linux/elf.h | grep 'struct dynamic';
607ca46e97a1b (David Howells         2012-10-13 10:46:48 +0100 143) typedef struct dynamic{

$ git log -1 607ca46e97a1b
commit 607ca46e97a1b6594b29647d98a32d545c24bdff
Author: David Howells <dhowells@redhat.com>
Date:   Sat Oct 13 10:46:48 2012 +0100

    UAPI: (Scripted) Disintegrate include/linux

    Signed-off-by: David Howells <dhowells@redhat.com>
    Acked-by: Arnd Bergmann <arnd@arndb.de>
    Acked-by: Thomas Gleixner <tglx@linutronix.de>
    Acked-by: Michael Kerrisk <mtk.manpages@gmail.com>
    Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Acked-by: Dave Jones <davej@redhat.com>

$ git show 607ca46e97a1b \
| grep -e ^diff -e 'struct dynamic' \
| grep -B1 'struct dynamic';
diff --git a/include/linux/elf.h b/include/linux/elf.h
-typedef struct dynamic{
--
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
+typedef struct dynamic{

struct dynamic is such a generic name that I don't think it's right to
expose it in UAPI headers, as anyone might reuse that tag for their
own purposes.  Should I prepare a patch?

Cheers,
Alex

P.S.:  Rolf, I added you because you changed the space in the struct
definition to make it easily greppable.  You may be interested in
using grepc(1), a shell script that does multiline greps of C
definitions (see this email for an example of how it works).  It's
the natural evolution of hand-made greps of C definitions, based
on pcre2grep(1).  It's imperfect, as any REGEX-based tool for this
probably is, but it's quite useful already.  :)

<http://www.alejandro-colomar.es/src/alx/alx/grepc.git/>

-- 
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