Commit 39be79c1 authored Oct 27, 2011 by Jeff Layton Committed by Christoph Hellwig Oct 28, 2011

vfs: iov_iter: have iov_iter_advance decrement nr_segs appropriately



Currently, when you call iov_iter_advance, then the pointer to the iovec
array can be incremented, but it does not decrement the nr_segs value in
the iov_iter struct. The result is a iov_iter struct with a nr_segs
value that goes beyond the end of the array.

While I'm not aware of anything that's specifically broken by this, it
seems odd and a bit dangerous not to decrement that value. If someone
were to trust the nr_segs value to be correct, then they could end up
walking off the end of the array.

Changing this might also provide some micro-optimization when dealing
with the last iovec in an array. Many of the other routines that deal
with iov_iter have optimized codepaths when nr_segs == 1.

Cc: Nick Piggin <npiggin@suse.de>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

parent c3b92c87

mm/filemap.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -2115,6 +2115,7 @@ void iov_iter_advance(struct iov_iter *i, size_t bytes)
		} else {
		const struct iovec *iov = i->iov;
		size_t base = i->iov_offset;
		unsigned long nr_segs = i->nr_segs;

		/*
		* The !iov->iov_len check ensures we skip over unlikely
		@@ -2130,11 +2131,13 @@ void iov_iter_advance(struct iov_iter *i, size_t bytes)
		base += copy;
		if (iov->iov_len == base) {
		iov++;
		nr_segs--;
		base = 0;
		}
		}
		i->iov = iov;
		i->iov_offset = base;
		i->nr_segs = nr_segs;
		}
		}
		EXPORT_SYMBOL(iov_iter_advance);

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