Commit a2362d24 authored Mar 14, 2013 by Michel Lespinasse Committed by Linus Torvalds Mar 14, 2013

mm/fremap.c: fix possible oops on error path



The vm_flags introduced in 6d7825b1 ("mm/fremap.c: fix oops on error
path") is supposed to avoid a compiler warning about unitialized
vm_flags without changing the generated code.

However I am concerned that this is going to be very brittle, and fail
with some compiler versions. The failure could be either of:

- compiler could actually load vma->vm_flags before checking for the
  !vma condition, thus reintroducing the oops

- compiler could optimize out the !vma check, since the pointer just got
  dereferenced shortly before (so the compiler knows it can't be NULL!)

I propose reversing this part of the change and initializing vm_flags to 0
just to avoid the bogus uninitialized use warning.

Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Tommi Rantala <tt.rantala@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent f4846e52

mm/fremap.c

+2 −3

Original line number	Diff line number	Diff line
		@@ -129,7 +129,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
		struct vm_area_struct *vma;
		int err = -EINVAL;
		int has_write_lock = 0;
		vm_flags_t vm_flags;
		vm_flags_t vm_flags = 0;

		if (prot)
		return err;
		@@ -163,8 +163,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
		* and that the remapped range is valid and fully within
		* the single existing vma.
		*/
		vm_flags = vma->vm_flags;
		if (!vma \|\| !(vm_flags & VM_SHARED))
		if (!vma \|\| !(vma->vm_flags & VM_SHARED))
		goto out;

		if (!vma->vm_ops \|\| !vma->vm_ops->remap_pages)

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