[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>
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2 changed files with 3 additions and 1 deletions
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@ -136,6 +136,7 @@ extern unsigned int kobjsize(const void *objp);
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#define VM_EXEC 0x00000004
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#define VM_SHARED 0x00000008
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/* mprotect() hardcodes VM_MAYREAD >> 4 == VM_READ, and so for r/w/x bits. */
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#define VM_MAYREAD 0x00000010 /* limits for mprotect() etc */
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#define VM_MAYWRITE 0x00000020
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#define VM_MAYEXEC 0x00000040
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@ -248,7 +248,8 @@ sys_mprotect(unsigned long start, size_t len, unsigned long prot)
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newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
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if ((newflags & ~(newflags >> 4)) & 0xf) {
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/* newflags >> 4 shift VM_MAY% in place of VM_% */
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if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
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error = -EACCES;
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goto out;
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}
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