From: David Laight <David.Laight@ACULAB.COM>
To: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: [RFC PATCH 00/12] Changes to code that reads iovec from userspace
Date: Tue, 31 Mar 2020 13:51:44 +0000 [thread overview]
Message-ID: <a2c781bbd5c44fd19483076fd0296943@AcuMS.aculab.com> (raw)
This is RFC because we seem to be in a merge window.
The canonical code to read iov[] is currently:
struct iovec iovstack[UIO_FASTIOV];
struct iovec *iov;
...
iov = iovstack;
rc = import_iovec(..., UIO_FASTIOV, &iov, &iter);
if (rc < 0)
return rc;
...
kfree(iov);
Note that the 'iov' parameter is used for two different things.
On input it is an iov[] can can be used.
On output it is an iov[] array that must be freed.
If 'iovstack' is passed, the count is actually always UIO_FASTIOV (8)
although in some places the array definition is in a different file
(never mind function) from the constant used.
import_iovec() itself is just a wrapper to rw_copy_check_uvector().
So everything is passed through to a second function.
Several items are 'passed by reference' - adding to the code paths.
On success import_iovec() returned the transfer count.
Only one caller looks at it, the count is also in iter.count.
The new canonical code is:
struct iov_cache cache;
struct iovec *iov;
...
iov = iovec_import(..., &cache, &iter);
if (IS_ERR(iov))
return PTR_ERR(iov);
...
kfree(iov);
Since 'struct iov_cache' is a fixed size there is no need to pass in
a length (correct or not!). It can still be NULL (used by the scsi code).
iovec_import() contains the code that used to be in rw_copy_check_uvector()
and then sets up the iov_iter.
rw_copy_check_uvector() is no more.
The only other caller was in mm/process_vm_access.c when reading the
iov[] for the target process addresses when copying from a differ process.
This can extract the iov[] from an extra 'struct iov_iter'.
In passing I noticed an access_ok() call on each fragment.
I hope this is just there to bail out early!
It is also skipped in process_vm_rw(). I did a quick look but couldn't
see an obvious equivalent check.
Patches 1 and 2 tidy up existing code.
Patches 3 and 4 add the new interface.
Patches 5 through 10 change all the callers.
Patch 11 removes a 'hack' that allowed fs/io_uring be updated before the socket code.
Patch 12 removes the old interface.
I suspect the changes need to trickle through a merge window.
David
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reply other threads:[~2020-03-31 13:51 UTC|newest]
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