| Message ID | 27be46ece36c42d6a7dabf62c6ac7a98@AcuMS.aculab.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Changes to code that reads iovec from userspace | expand |
So looking at the various callers I'm not sure this API is the
best. If we want to do something fancy I'd hide the struct iovec
instances entirely with something like:
struct iov_storage {
struct iovec stack[UIO_FASTIOV], *vec;
}
int iov_iter_import_iovec(struct iov_iter *iter, struct iov_storage *s,
const struct iovec __user *vec, unsigned long nr_segs,
int type);
and then add a new helper to free the thing if needed:
void iov_iter_release_iovec(struct iov_storage *s)
{
if (s->vec != s->stack)
kfree(s->vec);
}
From: Christoph Hellwig > Sent: 21 September 2020 15:22 > > So looking at the various callers I'm not sure this API is the > best. If we want to do something fancy I'd hide the struct iovec > instances entirely with something like: > > struct iov_storage { > struct iovec stack[UIO_FASTIOV], *vec; > } > > int iov_iter_import_iovec(struct iov_iter *iter, struct iov_storage *s, > const struct iovec __user *vec, unsigned long nr_segs, > int type); > > and then add a new helper to free the thing if needed: > > void iov_iter_release_iovec(struct iov_storage *s) > { > if (s->vec != s->stack) > kfree(s->vec); > } I didn't think of going that far. There are 2 call sites (in scsi) that don't pass the cache. Given that the 'buffer to free' address probably needs to be spilled to stack forcing in into an on-stack structure that is already passed by address is probably a good idea. The iov_iter_release_iovec() should be static inline and just: if (s->vec) kfree(s->vec); You want the test because 99.99% of the time it will be NULL. The kernel iov[] to use is iter.iov not part of the cache. That will be a bigger change on the io_uring code. (The patch I didn't write.) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
From: Christoph Hellwig > Sent: 21 September 2020 15:22 > > So looking at the various callers I'm not sure this API is the > best. If we want to do something fancy I'd hide the struct iovec > instances entirely with something like: > > struct iov_storage { > struct iovec stack[UIO_FASTIOV], *vec; > } > > int iov_iter_import_iovec(struct iov_iter *iter, struct iov_storage *s, > const struct iovec __user *vec, unsigned long nr_segs, > int type); > > and then add a new helper to free the thing if needed: > > void iov_iter_release_iovec(struct iov_storage *s) > { > if (s->vec != s->stack) > kfree(s->vec); > } I've been looking at this code again now most of the pending changes are in Linus's tree. I was actually looking at going one stage further. The 'iov_iter' is always allocated with the 'iov_storage' *above). Usually both are on the callers stack - possibly in different functions. So add: struct iovec_iter { struct iov_iter iter; struct iovec to_free; struct iovec stack[UIO_FASTIOV]; }; int __iovec_import(struct iovec_iter *, const struct iovec __user *vec, unsigned long nr_segs, int type, bool compat); And a 'clean' function to do kfree(iovec->to_free); This reduces the complexity of most of the callers. I started doing the changes, but got in a mess in io_uring.c (as usual). I think I've got a patch pending (in my brain) to simplify the io_uring code. The plan is to add: if (iter->iov != xxx->to_free) iter->iov = xxx->stack; Prior to every use of the iter. This fixes up anything that got broken by a memcpy() of the fields. The tidyup code is then always kfree(xxx->to_free). David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c index ef722f04f88a..0343918a84d3 100644 --- a/block/scsi_ioctl.c +++ b/block/scsi_ioctl.c @@ -331,20 +331,22 @@ static int sg_io(struct request_queue *q, struct gendisk *bd_disk, ret = 0; if (hdr->iovec_count) { struct iov_iter i; - struct iovec *iov = NULL; + struct iovec *iov; #ifdef CONFIG_COMPAT if (in_compat_syscall()) - ret = compat_import_iovec(rq_data_dir(rq), + iov = compat_iovec_import(rq_data_dir(rq), hdr->dxferp, hdr->iovec_count, - 0, &iov, &i); + NULL, &i); else #endif - ret = import_iovec(rq_data_dir(rq), + iov = iovec_import(rq_data_dir(rq), hdr->dxferp, hdr->iovec_count, - 0, &iov, &i); - if (ret < 0) + NULL, &i); + if (IS_ERR(iov)) { + ret = PTR_ERR(iov); goto out_free_cdb; + } /* SG_IO howto says that the shorter of the two wins */ iov_iter_truncate(&i, hdr->dxfer_len); diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c index 20472aaaf630..1dbc0a74add5 100644 --- a/drivers/scsi/sg.c +++ b/drivers/scsi/sg.c @@ -1817,19 +1817,19 @@ sg_start_req(Sg_request *srp, unsigned char *cmd) } if (iov_count) { - struct iovec *iov = NULL; + struct iovec *iov; struct iov_iter i; #ifdef CONFIG_COMPAT if (in_compat_syscall()) - res = compat_import_iovec(rw, hp->dxferp, iov_count, - 0, &iov, &i); + iov = compat_iovec_import(rw, hp->dxferp, iov_count, + NULL, &i); else #endif - res = import_iovec(rw, hp->dxferp, iov_count, - 0, &iov, &i); - if (res < 0) - return res; + iov = iovec_import(rw, hp->dxferp, iov_count, + NULL, &i); + if (IS_ERR(iov)) + return PTR_ERR(iov); iov_iter_truncate(&i, hp->dxfer_len); if (!iov_iter_count(&i)) {
iovec_import() has a safer calling convention than import_iovec(). Signed-off-by: David Laight <david.laight@aculab.com> --- block/scsi_ioctl.c | 14 ++++++++------ drivers/scsi/sg.c | 14 +++++++------- 2 files changed, 15 insertions(+), 13 deletions(-)