[34-longterm 135/260] aio: check for multiplication overflow in do_io_submit

[Paul Gortmaker]

From: Jeff Moyer <jmoyer@xxxxxxxxxx>

commit 75e1c70fc31490ef8a373ea2a4bea2524099b478 upstream.

Tavis Ormandy pointed out that do_io_submit does not do proper bounds
checking on the passed-in iocb array:

   Âif (unlikely(nr < 0))
       Âreturn -EINVAL;

   Âif (unlikely(!access_ok(VERIFY_READ, iocbpp, (nr*sizeof(iocbpp)))))
       Âreturn -EFAULT;           Â^^^^^^^^^^^^^^^^^^

The attached patch checks for overflow, and if it is detected, the
number of iocbs submitted is scaled down to a number that will fit in
the long. ÂThis is an ok thing to do, as sys_io_submit is documented as
returning the number of iocbs submitted, so callers should handle a
return value of less than the 'nr' argument passed in.

Reported-by: Tavis Ormandy <taviso@xxxxxxxxxxxxx>
Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 fs/aio.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 48fdeeb..94b6cd6 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1659,6 +1659,9 @@ long do_io_submit(aio_context_t ctx_id, long nr,
 	if (unlikely(nr < 0))
 		return -EINVAL;
 
+	if (unlikely(nr > LONG_MAX/sizeof(*iocbpp)))
+		nr = LONG_MAX/sizeof(*iocbpp);
+
 	if (unlikely(!access_ok(VERIFY_READ, iocbpp, (nr*sizeof(*iocbpp)))))
 		return -EFAULT;
 
-- 
1.7.3.3

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