tree d1bbf5d64c4eaee7bfefae22ad87b96967187cc8
parent 0056e65f9e28d83ee1a3fb4f7d0041e838f03c34
author Linus Torvalds <torvalds@linux-foundation.org> 1217454312 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> 1217454618 -0700

Fix off-by-one error in iov_iter_advance()

The iov_iter_advance() function would look at the iov->iov_len entry
even though it might have iterated over the whole array, and iov was
pointing past the end.  This would cause DEBUG_PAGEALLOC to trigger a
kernel page fault if the allocation was at the end of a page, and the
next page was unallocated.

The quick fix is to just change the order of the tests: check that there
is any iovec data left before we check the iov entry itself.

Thanks to Alexey Dobriyan for finding this case, and testing the fix.

Reported-and-tested-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@kernel.org> [2.6.25.x, 2.6.26.x]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>