Commit 0b86dbf6 authored by Al Viro's avatar Al Viro Committed by Linus Torvalds

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: default avatarTheodore Tso <>
Signed-off-by: default avatarAl Viro <>
Tested-by: default avatarAlan Cox <>
Tested-by: default avatarBruno Wolff III <>
Signed-off-by: default avatarLinus Torvalds <>
parent d7933ab7
......@@ -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;
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