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SubjectRe: [PATCH] 2.5.27 read_write
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On Mon, 2002-07-22 at 15:08, Marcin Dalecki wrote:
> - This is making the read_write.c C.
>
> - It is fixing completely confused wild casting to 32 bits.
>
> - Actually adding a comment explaining the obscure code, which is
> relying on integer arithmetics overflow.

This is the 2.4 patch. This passes the SuS LSB validation tests and gets
32/64bit behaviour as well as sign rules for iov_len elements right. At
least I hope it does.

--- linux-2.5.27/fs/read_write.c Sat Jul 20 20:11:25 2002
+++ linux-2.5.27-ac1/fs/read_write.c Mon Jul 22 15:43:46 2002
@@ -301,17 +301,23 @@
if (copy_from_user(iov, vector, count*sizeof(*vector)))
goto out;

- /* BSD readv/writev returns EINVAL if one of the iov_len
- values < 0 or tot_len overflowed a 32-bit integer. -ink */
+ /*
+ * Single unix specification:
+ * We should -EINVAL if an element length is not >= 0 and fitting an ssize_t
+ * The total length is fitting an ssize_t
+ *
+ * Be careful here because iov_len is a size_t not an ssize_t
+ */
+
tot_len = 0;
ret = -EINVAL;
for (i = 0 ; i < count ; i++) {
- size_t tmp = tot_len;
- int len = iov[i].iov_len;
- if (len < 0)
+ ssize_t tmp = tot_len;
+ ssize_t len = (ssize_t)iov[i].iov_len;
+ if (len < 0) /* size_t not fitting an ssize_t .. */
goto out;
- (u32)tot_len += len;
- if (tot_len < tmp || tot_len < (u32)len)
+ tot_len += len;
+ if (tot_len < tmp) /* maths overflow on the ssize_t */
goto out;
}

-
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