vfs: iov_iter: have iov_iter_advance decrement nr_segs appropriately
authorJeff Layton <jlayton@redhat.com>
Thu, 27 Oct 2011 21:53:08 +0000 (23:53 +0200)
committerChristoph Hellwig <hch@serles.lst.de>
Fri, 28 Oct 2011 11:55:08 +0000 (13:55 +0200)
commit39be79c16f2b8eb07dd0d4e965cddfe39cc0534a
tree821611221295d47c671ec72e1fb558efcedff03b
parentc3b92c8787367a8bb53d57d9789b558f1295cc96
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>
mm/filemap.c