fix fault_in_multipages_...() on architectures with no-op access_ok()

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[ Upstream commit e23d4159b1 ]

Switching iov_iter fault-in to multipages variants has exposed an old
bug in underlying fault_in_multipages_...(); they break if the range
passed to them wraps around.  Normally access_ok() done by callers will
prevent such (and it's a guaranteed EFAULT - ERR_PTR() values fall into
such a range and they should not point to any valid objects).

However, on architectures where userland and kernel live in different
MMU contexts (e.g. s390) access_ok() is a no-op and on those a range
with a wraparound can reach fault_in_multipages_...().

Since any wraparound means EFAULT there, the fix is trivial - turn
those

    while (uaddr <= end)
	    ...
into

    if (unlikely(uaddr > end))
	    return -EFAULT;
    do
	    ...
    while (uaddr <= end);

Reported-by: Jan Stancek <jstancek@redhat.com>
Tested-by: Jan Stancek <jstancek@redhat.com>
Cc: stable@vger.kernel.org # v3.5+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>

...

This commit is contained in:

Al Viro 2016-09-20 20:07:42 +01:00 • committed by Sasha Levin

parent 1108f7038c

commit 400f32af8f

1 changed files with 19 additions and 19 deletions

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38

include/linux/pagemap.h

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