Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 7e2cff42 authored Sep 21, 2005 by Paolo 'Blaisorblade' Giarrusso Committed by Linus Torvalds Sep 21, 2005

[PATCH] mm: add a note about partially hardcoded VM_* flags



Hugh made me note this line for permission checking in mprotect():

		if ((newflags & ~(newflags >> 4)) & 0xf) {

after figuring out what's that about, I decided it's nasty enough.  Btw
Hugh itself didn't like the 0xf.

We can safely change it to VM_READ|VM_WRITE|VM_EXEC because we never change
VM_SHARED, so no need to check that.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Acked-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent 7e871b6c

include/linux/mm.h

+1 −0

Original line number	Original line	Diff line number	Diff line
	@@ -136,6 +136,7 @@ extern unsigned int kobjsize(const void *objp);
	#define VM_EXEC 0x00000004		#define VM_EXEC 0x00000004
	#define VM_SHARED 0x00000008		#define VM_SHARED 0x00000008

			/* mprotect() hardcodes VM_MAYREAD >> 4 == VM_READ, and so for r/w/x bits. */
	#define VM_MAYREAD 0x00000010 /* limits for mprotect() etc */		#define VM_MAYREAD 0x00000010 /* limits for mprotect() etc */
	#define VM_MAYWRITE 0x00000020		#define VM_MAYWRITE 0x00000020
	#define VM_MAYEXEC 0x00000040		#define VM_MAYEXEC 0x00000040

mm/mprotect.c

+2 −1

Original line number	Original line	Diff line number	Diff line
	@@ -248,7 +248,8 @@ sys_mprotect(unsigned long start, size_t len, unsigned long prot)

	newflags = vm_flags \| (vma->vm_flags & ~(VM_READ \| VM_WRITE \| VM_EXEC));		newflags = vm_flags \| (vma->vm_flags & ~(VM_READ \| VM_WRITE \| VM_EXEC));

	if ((newflags & ~(newflags >> 4)) & 0xf) {		/* newflags >> 4 shift VM_MAY% in place of VM_% */
			if ((newflags & ~(newflags >> 4)) & (VM_READ \| VM_WRITE \| VM_EXEC)) {
	error = -EACCES;		error = -EACCES;
	goto out;		goto out;
	}		}