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Commit bc917be8 authored by Al Viro's avatar Al Viro
Browse files

saner iov_iter initialization primitives 



iovec-backed iov_iter instances are assumed to satisfy several properties:
	* no more than UIO_MAXIOV elements in iovec array
	* total size of all ranges is no more than MAX_RW_COUNT
	* all ranges pass access_ok().

The problem is, invariants of data structures should be established in the
primitives creating those data structures, not in the code using those
primitives.  And iov_iter_init() violates that principle.  For a while we
managed to get away with that, but once the use of iov_iter started to
spread, it didn't take long for shit to hit the fan - missed check in
sys_sendto() had introduced a roothole.

We _do_ have primitives for importing and validating iovecs (both native and
compat ones) and those primitives are almost always followed by shoving the
resulting iovec into iov_iter.  Life would be considerably simpler (and safer)
if we combined those primitives with initializing iov_iter.

That gives us two new primitives - import_iovec() and compat_import_iovec().
Calling conventions:
	iovec = iov_array;
	err = import_iovec(direction, uvec, nr_segs,
			   ARRAY_SIZE(iov_array), &iovec,
			   &iter);
imports user vector into kernel space (into iov_array if it fits, allocated
if it doesn't fit or if iovec was NULL), validates it and sets iter up to
refer to it.  On success 0 is returned and allocated kernel copy (or NULL
if the array had fit into caller-supplied one) is returned via iovec.
On failure all allocations are undone and -E... is returned.  If the total
size of ranges exceeds MAX_RW_COUNT, the excess is silently truncated.

compat_import_iovec() expects uvec to be a pointer to user array of compat_iovec;
otherwise it's identical to import_iovec().

Finally, import_single_range() sets iov_iter backed by single-element iovec
covering a user-supplied range -

	err = import_single_range(direction, address, size, iovec, &iter);

does validation and sets iter up.  Again, size in excess of MAX_RW_COUNT gets
silently truncated.

Next commits will be switching the things up to use of those and reducing
the amount of iov_iter_init() instances.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent d879cb83

include/linux/uio.h

+14 −0
Original line number Diff line number Diff line
@@ -139,4 +139,18 @@ static inline void iov_iter_reexpand(struct iov_iter *i, size_t count) 
size_t csum_and_copy_to_iter(void *addr, size_t bytes, __wsum *csum, struct iov_iter *i);

size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum, struct iov_iter *i);



int import_iovec(int type, const struct iovec __user * uvector,

		 unsigned nr_segs, unsigned fast_segs,

		 struct iovec **iov, struct iov_iter *i);



#ifdef CONFIG_COMPAT

struct compat_iovec;

int compat_import_iovec(int type, const struct compat_iovec __user * uvector,

		 unsigned nr_segs, unsigned fast_segs,

		 struct iovec **iov, struct iov_iter *i);

#endif



int import_single_range(int type, void __user *buf, size_t len,

		 struct iovec *iov, struct iov_iter *i);



#endif

lib/iov_iter.c

+57 −0
Original line number Diff line number Diff line
@@ -766,3 +766,60 @@ const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags) 
				   flags);

}

EXPORT_SYMBOL(dup_iter);



int import_iovec(int type, const struct iovec __user * uvector,

		 unsigned nr_segs, unsigned fast_segs,

		 struct iovec **iov, struct iov_iter *i)

{

	ssize_t n;

	struct iovec *p;

	n = rw_copy_check_uvector(type, uvector, nr_segs, fast_segs,

				  *iov, &p);

	if (n < 0) {

		if (p != *iov)

			kfree(p);

		*iov = NULL;

		return n;

	}

	iov_iter_init(i, type, p, nr_segs, n);

	*iov = p == *iov ? NULL : p;

	return 0;

}

EXPORT_SYMBOL(import_iovec);



#ifdef CONFIG_COMPAT

#include <linux/compat.h>



int compat_import_iovec(int type, const struct compat_iovec __user * uvector,

		 unsigned nr_segs, unsigned fast_segs,

		 struct iovec **iov, struct iov_iter *i)

{

	ssize_t n;

	struct iovec *p;

	n = compat_rw_copy_check_uvector(type, uvector, nr_segs, fast_segs,

				  *iov, &p);

	if (n < 0) {

		if (p != *iov)

			kfree(p);

		*iov = NULL;

		return n;

	}

	iov_iter_init(i, type, p, nr_segs, n);

	*iov = p == *iov ? NULL : p;

	return 0;

}

#endif



int import_single_range(int rw, void __user *buf, size_t len,

		 struct iovec *iov, struct iov_iter *i)

{

	if (len > MAX_RW_COUNT)

		len = MAX_RW_COUNT;

	if (unlikely(!access_ok(!rw, buf, len)))

		return -EFAULT;



	iov->iov_base = buf;

	iov->iov_len = len;

	iov_iter_init(i, rw, iov, 1, len);

	return 0;

}