The patch titled
mm: iov_iter: have iov_iter_advance() decrement nr_segs appropriately
has been added to the -mm tree. Its filename is
iov_iter-have-iov_iter_advance-decrement-nr_segs-appropriately.patch
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Subject: mm: iov_iter: have iov_iter_advance() decrement nr_segs appropriately
From: Jeff Layton <jlayton@xxxxxxxxxx>
Currently, when you call iov_iter_advance, then the pointer to the kvec
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 kvec in an array. Many of the other routines that deal with
iov_iter have optimized codepaths when nr_segs == 1.
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 3 +++
1 file changed, 3 insertions(+)
diff -puN mm/filemap.c~iov_iter-have-iov_iter_advance-decrement-nr_segs-appropriately mm/filemap.c
--- a/mm/filemap.c~iov_iter-have-iov_iter_advance-decrement-nr_segs-appropriately
+++ a/mm/filemap.c
@@ -2113,6 +2113,7 @@ void iov_iter_advance(struct iov_iter *i
} 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
@@ -2128,11 +2129,13 @@ void iov_iter_advance(struct iov_iter *i
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);
_
Patches currently in -mm which might be from jlayton@xxxxxxxxxx are
linux-next.patch
iov_iter-have-iov_iter_advance-decrement-nr_segs-appropriately.patch
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