From 0b86dbf675e0170a191a9ca18e5e99fd39a678c0 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Mon, 23 Jun 2014 08:44:40 +0100 Subject: [PATCH] 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 Signed-off-by: Al Viro Tested-by: Alan Cox Tested-by: Bruno Wolff III Signed-off-by: Linus Torvalds --- include/linux/uio.h | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/include/linux/uio.h b/include/linux/uio.h index e2231e47cec1..d54985e0705e 100644 --- a/include/linux/uio.h +++ b/include/linux/uio.h @@ -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; } -- 2.20.1