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

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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>
This commit is contained in:
Paolo 'Blaisorblade' Giarrusso 2005-09-21 09:55:39 -07:00 committed by Linus Torvalds
parent 7e871b6c8f
commit 7e2cff42cf
2 changed files with 3 additions and 1 deletions
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1
include/linux/mm.h
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@ -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

3
mm/mprotect.c
View file

@ -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;
} }