iov_iter_advance() fix
 

Bug: #231746

Picked from linux-2.6.24.y b6845726368e5b7b086e6d6438c9380bf5b7bc1c
commit: f7009264c519603b8ec67c881bd368a56703cfc9 upstream

iov_iter_advance() skips over zero-length iovecs, however it does not properly
terminate at the end of the iovec array. Fix this by checking against
i->count before we skip a zero-length iov.

The bug was reproduced with a test program that continually randomly creates
iovs to writev. The fix was also verified with the same program and also it
could verify that the correct data was contained in the file after each
writev.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Tested-by: "Kevin Coffman" <kwc@citi.umich.edu>
Cc: "Alexey Dobriyan" <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
---
mm/filemap.c | 22 ++++++++++------------
1 files changed, 10 insertions(+), 12 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 69430d2..76b036f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1725,21 +1725,27 @@ size_t iov_iter_copy_from_user(struct page *page,
}
EXPORT_SYMBOL(iov_iter_copy_from_user);

-static void __iov_iter_advance_iov(struct iov_iter *i, size_t bytes)
+void iov_iter_advance(struct iov_iter *i, size_t bytes)
{
+ BUG_ON(i->count < bytes);
+
if (likely(i->nr_segs == 1)) {
i->iov_offset += bytes;
+ i->count -= bytes;
} else {
const struct iovec *iov = i->iov;
size_t base = i->iov_offset;

/*
* The !iov->iov_len check ensures we skip over unlikely
- * zero-length segments.
+ * zero-length segments (without overruning the iovec).
*/
- while (bytes || !iov->iov_len) {
- int copy = min(bytes, iov->iov_len - base);
+ while (bytes || unlikely(!iov->iov_len && i->count)) {
+ int copy;

+ copy = min(bytes, iov->iov_len - base);
+ BUG_ON(!i->count || i->count < copy);
+ i->count -= copy;
bytes -= copy;
base += copy;
if (iov->iov_len == base) {
@@ -1751,14 +1757,6 @@ static void __iov_iter_advance_iov(struct iov_iter *i, size_t bytes)
i->iov_offset = base;
}
}
-
-void iov_iter_advance(struct iov_iter *i, size_t bytes)
-{
- BUG_ON(i->count < bytes);
-
- __iov_iter_advance_iov(i, bytes);
- i->count -= bytes;
-}
EXPORT_SYMBOL(iov_iter_advance);

/*
--
1.5.4.3


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