Messages in this thread | | | From | David Laight <> | Subject | [RFC PATCH 00/12] Changes to code that reads iovec from userspace | Date | Tue, 31 Mar 2020 13:51:44 +0000 |
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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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