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iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c
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This lets the compiler inline it into import_iovec() generating
much better code.

Signed-off-by: David Laight <david.laight@aculab.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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David Laight authored and Al Viro committed Sep 25, 2020
1 parent 576d070 commit fb041b5
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Showing 2 changed files with 176 additions and 179 deletions.
179 changes: 0 additions & 179 deletions fs/read_write.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -752,185 +752,6 @@ static ssize_t do_loop_readv_writev(struct file *filp, struct iov_iter *iter,
return ret;
}

/**
* rw_copy_check_uvector() - Copy an array of &struct iovec from userspace
* into the kernel and check that it is valid.
*
* @type: One of %CHECK_IOVEC_ONLY, %READ, or %WRITE.
* @uvector: Pointer to the userspace array.
* @nr_segs: Number of elements in userspace array.
* @fast_segs: Number of elements in @fast_pointer.
* @fast_pointer: Pointer to (usually small on-stack) kernel array.
* @ret_pointer: (output parameter) Pointer to a variable that will point to
* either @fast_pointer, a newly allocated kernel array, or NULL,
* depending on which array was used.
*
* This function copies an array of &struct iovec of @nr_segs from
* userspace into the kernel and checks that each element is valid (e.g.
* it does not point to a kernel address or cause overflow by being too
* large, etc.).
*
* As an optimization, the caller may provide a pointer to a small
* on-stack array in @fast_pointer, typically %UIO_FASTIOV elements long
* (the size of this array, or 0 if unused, should be given in @fast_segs).
*
* @ret_pointer will always point to the array that was used, so the
* caller must take care not to call kfree() on it e.g. in case the
* @fast_pointer array was used and it was allocated on the stack.
*
* Return: The total number of bytes covered by the iovec array on success
* or a negative error code on error.
*/
ssize_t rw_copy_check_uvector(int type, const struct iovec __user * uvector,
unsigned long nr_segs, unsigned long fast_segs,
struct iovec *fast_pointer,
struct iovec **ret_pointer)
{
unsigned long seg;
ssize_t ret;
struct iovec *iov = fast_pointer;

/*
* SuS says "The readv() function *may* fail if the iovcnt argument
* was less than or equal to 0, or greater than {IOV_MAX}. Linux has
* traditionally returned zero for zero segments, so...
*/
if (nr_segs == 0) {
ret = 0;
goto out;
}

/*
* First get the "struct iovec" from user memory and
* verify all the pointers
*/
if (nr_segs > UIO_MAXIOV) {
ret = -EINVAL;
goto out;
}
if (nr_segs > fast_segs) {
iov = kmalloc_array(nr_segs, sizeof(struct iovec), GFP_KERNEL);
if (iov == NULL) {
ret = -ENOMEM;
goto out;
}
}
if (copy_from_user(iov, uvector, nr_segs*sizeof(*uvector))) {
ret = -EFAULT;
goto out;
}

/*
* According to the Single Unix Specification we should return EINVAL
* if an element length is < 0 when cast to ssize_t or if the
* total length would overflow the ssize_t return value of the
* system call.
*
* Linux caps all read/write calls to MAX_RW_COUNT, and avoids the
* overflow case.
*/
ret = 0;
for (seg = 0; seg < nr_segs; seg++) {
void __user *buf = iov[seg].iov_base;
ssize_t len = (ssize_t)iov[seg].iov_len;

/* see if we we're about to use an invalid len or if
* it's about to overflow ssize_t */
if (len < 0) {
ret = -EINVAL;
goto out;
}
if (type >= 0
&& unlikely(!access_ok(buf, len))) {
ret = -EFAULT;
goto out;
}
if (len > MAX_RW_COUNT - ret) {
len = MAX_RW_COUNT - ret;
iov[seg].iov_len = len;
}
ret += len;
}
out:
*ret_pointer = iov;
return ret;
}

#ifdef CONFIG_COMPAT
ssize_t compat_rw_copy_check_uvector(int type,
const struct compat_iovec __user *uvector, unsigned long nr_segs,
unsigned long fast_segs, struct iovec *fast_pointer,
struct iovec **ret_pointer)
{
compat_ssize_t tot_len;
struct iovec *iov = *ret_pointer = fast_pointer;
ssize_t ret = 0;
int seg;

/*
* SuS says "The readv() function *may* fail if the iovcnt argument
* was less than or equal to 0, or greater than {IOV_MAX}. Linux has
* traditionally returned zero for zero segments, so...
*/
if (nr_segs == 0)
goto out;

ret = -EINVAL;
if (nr_segs > UIO_MAXIOV)
goto out;
if (nr_segs > fast_segs) {
ret = -ENOMEM;
iov = kmalloc_array(nr_segs, sizeof(struct iovec), GFP_KERNEL);
if (iov == NULL)
goto out;
}
*ret_pointer = iov;

ret = -EFAULT;
if (!access_ok(uvector, nr_segs*sizeof(*uvector)))
goto out;

/*
* Single unix specification:
* We should -EINVAL if an element length is not >= 0 and fitting an
* ssize_t.
*
* In Linux, the total length is limited to MAX_RW_COUNT, there is
* no overflow possibility.
*/
tot_len = 0;
ret = -EINVAL;
for (seg = 0; seg < nr_segs; seg++) {
compat_uptr_t buf;
compat_ssize_t len;

if (__get_user(len, &uvector->iov_len) ||
__get_user(buf, &uvector->iov_base)) {
ret = -EFAULT;
goto out;
}
if (len < 0) /* size_t not fitting in compat_ssize_t .. */
goto out;
if (type >= 0 &&
!access_ok(compat_ptr(buf), len)) {
ret = -EFAULT;
goto out;
}
if (len > MAX_RW_COUNT - tot_len)
len = MAX_RW_COUNT - tot_len;
tot_len += len;
iov->iov_base = compat_ptr(buf);
iov->iov_len = (compat_size_t) len;
uvector++;
iov++;
}
ret = tot_len;

out:
return ret;
}
#endif

static ssize_t do_iter_read(struct file *file, struct iov_iter *iter,
loff_t *pos, rwf_t flags)
{
Expand Down
176 changes: 176 additions & 0 deletions lib/iov_iter.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1650,6 +1650,109 @@ const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags)
}
EXPORT_SYMBOL(dup_iter);

/**
* rw_copy_check_uvector() - Copy an array of &struct iovec from userspace
* into the kernel and check that it is valid.
*
* @type: One of %CHECK_IOVEC_ONLY, %READ, or %WRITE.
* @uvector: Pointer to the userspace array.
* @nr_segs: Number of elements in userspace array.
* @fast_segs: Number of elements in @fast_pointer.
* @fast_pointer: Pointer to (usually small on-stack) kernel array.
* @ret_pointer: (output parameter) Pointer to a variable that will point to
* either @fast_pointer, a newly allocated kernel array, or NULL,
* depending on which array was used.
*
* This function copies an array of &struct iovec of @nr_segs from
* userspace into the kernel and checks that each element is valid (e.g.
* it does not point to a kernel address or cause overflow by being too
* large, etc.).
*
* As an optimization, the caller may provide a pointer to a small
* on-stack array in @fast_pointer, typically %UIO_FASTIOV elements long
* (the size of this array, or 0 if unused, should be given in @fast_segs).
*
* @ret_pointer will always point to the array that was used, so the
* caller must take care not to call kfree() on it e.g. in case the
* @fast_pointer array was used and it was allocated on the stack.
*
* Return: The total number of bytes covered by the iovec array on success
* or a negative error code on error.
*/
ssize_t rw_copy_check_uvector(int type, const struct iovec __user *uvector,
unsigned long nr_segs, unsigned long fast_segs,
struct iovec *fast_pointer, struct iovec **ret_pointer)
{
unsigned long seg;
ssize_t ret;
struct iovec *iov = fast_pointer;

/*
* SuS says "The readv() function *may* fail if the iovcnt argument
* was less than or equal to 0, or greater than {IOV_MAX}. Linux has
* traditionally returned zero for zero segments, so...
*/
if (nr_segs == 0) {
ret = 0;
goto out;
}

/*
* First get the "struct iovec" from user memory and
* verify all the pointers
*/
if (nr_segs > UIO_MAXIOV) {
ret = -EINVAL;
goto out;
}
if (nr_segs > fast_segs) {
iov = kmalloc_array(nr_segs, sizeof(struct iovec), GFP_KERNEL);
if (iov == NULL) {
ret = -ENOMEM;
goto out;
}
}
if (copy_from_user(iov, uvector, nr_segs*sizeof(*uvector))) {
ret = -EFAULT;
goto out;
}

/*
* According to the Single Unix Specification we should return EINVAL
* if an element length is < 0 when cast to ssize_t or if the
* total length would overflow the ssize_t return value of the
* system call.
*
* Linux caps all read/write calls to MAX_RW_COUNT, and avoids the
* overflow case.
*/
ret = 0;
for (seg = 0; seg < nr_segs; seg++) {
void __user *buf = iov[seg].iov_base;
ssize_t len = (ssize_t)iov[seg].iov_len;

/* see if we we're about to use an invalid len or if
* it's about to overflow ssize_t */
if (len < 0) {
ret = -EINVAL;
goto out;
}
if (type >= 0
&& unlikely(!access_ok(buf, len))) {
ret = -EFAULT;
goto out;
}
if (len > MAX_RW_COUNT - ret) {
len = MAX_RW_COUNT - ret;
iov[seg].iov_len = len;
}
ret += len;
}
out:
*ret_pointer = iov;
return ret;
}

/**
* import_iovec() - Copy an array of &struct iovec from userspace
* into the kernel, check that it is valid, and initialize a new
Expand Down Expand Up @@ -1695,6 +1798,79 @@ EXPORT_SYMBOL(import_iovec);
#ifdef CONFIG_COMPAT
#include <linux/compat.h>

ssize_t compat_rw_copy_check_uvector(int type,
const struct compat_iovec __user *uvector,
unsigned long nr_segs, unsigned long fast_segs,
struct iovec *fast_pointer, struct iovec **ret_pointer)
{
compat_ssize_t tot_len;
struct iovec *iov = *ret_pointer = fast_pointer;
ssize_t ret = 0;
int seg;

/*
* SuS says "The readv() function *may* fail if the iovcnt argument
* was less than or equal to 0, or greater than {IOV_MAX}. Linux has
* traditionally returned zero for zero segments, so...
*/
if (nr_segs == 0)
goto out;

ret = -EINVAL;
if (nr_segs > UIO_MAXIOV)
goto out;
if (nr_segs > fast_segs) {
ret = -ENOMEM;
iov = kmalloc_array(nr_segs, sizeof(struct iovec), GFP_KERNEL);
if (iov == NULL)
goto out;
}
*ret_pointer = iov;

ret = -EFAULT;
if (!access_ok(uvector, nr_segs*sizeof(*uvector)))
goto out;

/*
* Single unix specification:
* We should -EINVAL if an element length is not >= 0 and fitting an
* ssize_t.
*
* In Linux, the total length is limited to MAX_RW_COUNT, there is
* no overflow possibility.
*/
tot_len = 0;
ret = -EINVAL;
for (seg = 0; seg < nr_segs; seg++) {
compat_uptr_t buf;
compat_ssize_t len;

if (__get_user(len, &uvector->iov_len) ||
__get_user(buf, &uvector->iov_base)) {
ret = -EFAULT;
goto out;
}
if (len < 0) /* size_t not fitting in compat_ssize_t .. */
goto out;
if (type >= 0 &&
!access_ok(compat_ptr(buf), len)) {
ret = -EFAULT;
goto out;
}
if (len > MAX_RW_COUNT - tot_len)
len = MAX_RW_COUNT - tot_len;
tot_len += len;
iov->iov_base = compat_ptr(buf);
iov->iov_len = (compat_size_t) len;
uvector++;
iov++;
}
ret = tot_len;

out:
return ret;
}

ssize_t compat_import_iovec(int type,
const struct compat_iovec __user * uvector,
unsigned nr_segs, unsigned fast_segs,
Expand Down

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