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Fix 32-bit regression in block device read(2) 

blkdev_read_iter() wants to cap the iov_iter by the amount of data
remaining to the end of device.  That's what iov_iter_truncate() is for
(trim iter->count if it's above the given limit).  So far, so good, but
the argument of iov_iter_truncate() is size_t, so on 32bit boxen (in
case of a large device) we end up with that upper limit truncated down
to 32 bits *before* comparing it with iter->count.

Easily fixed by making iov_iter_truncate() take 64bit argument - it does
the right thing after such change (we only reach the assignment in there
when the current value of iter->count is greater than the limit, i.e.
for anything that would get truncated we don't reach the assignment at
all) and that argument is not the new value of iter->count - it's an
upper limit for such.

The overhead of passing u64 is not an issue - the thing is inlined, so
callers passing size_t won't pay any penalty.

Reported-and-tested-by: Theodore Tso <tytso@mit.edu>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Tested-by: Bruno Wolff III <bruno@wolff.to>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
hifive-unleashed-5.1
Al Viro 2014-06-23 08:44:40 +01:00 committed by Linus Torvalds
parent d7933ab727
commit 0b86dbf675
1 changed files with 13 additions and 1 deletions
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14
include/linux/uio.h
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@ -94,8 +94,20 @@ static inline size_t iov_iter_count(struct iov_iter *i)
return i->count;
}
static inline void iov_iter_truncate(struct iov_iter *i, size_t count)
/*
* Cap the iov_iter by given limit; note that the second argument is
* *not* the new size - it's upper limit for such. Passing it a value
* greater than the amount of data in iov_iter is fine - it'll just do
* nothing in that case.
*/
static inline void iov_iter_truncate(struct iov_iter *i, u64 count)
{
/*
* count doesn't have to fit in size_t - comparison extends both
* operands to u64 here and any value that would be truncated by
* conversion in assignement is by definition greater than all
* values of size_t, including old i->count.
*/
if (i->count > count)
i->count = count;
}