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fs: don't allow kernel reads and writes without iter ops 

Don't allow calling ->read or ->write with set_fs as a preparation for
killing off set_fs.  All the instances that we use kernel_read/write on
are using the iter ops already.

If a file has both the regular ->read/->write methods and the iter
variants those could have different semantics for messed up enough
drivers.  Also fails the kernel access to them in that case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Christoph Hellwig 2020-09-03 16:22:33 +02:00 committed by Al Viro
parent 4bd6a7353e
commit 4d03e3cc59
1 changed files with 42 additions and 25 deletions
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67
fs/read_write.c
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@ -419,27 +419,41 @@ static ssize_t new_sync_read(struct file *filp, char __user *buf, size_t len, lo
return ret;
}
static int warn_unsupported(struct file *file, const char *op)
{
pr_warn_ratelimited(
"kernel %s not supported for file %pD4 (pid: %d comm: %.20s)\n",
op, file, current->pid, current->comm);
return -EINVAL;
}
ssize_t __kernel_read(struct file *file, void *buf, size_t count, loff_t *pos)
{
mm_segment_t old_fs = get_fs();
struct kvec iov = {
.iov_base = buf,
.iov_len = min_t(size_t, count, MAX_RW_COUNT),
};
struct kiocb kiocb;
struct iov_iter iter;
ssize_t ret;
if (WARN_ON_ONCE(!(file->f_mode & FMODE_READ)))
return -EINVAL;
if (!(file->f_mode & FMODE_CAN_READ))
return -EINVAL;
/*
* Also fail if ->read_iter and ->read are both wired up as that
* implies very convoluted semantics.
*/
if (unlikely(!file->f_op->read_iter || file->f_op->read))
return warn_unsupported(file, "read");
if (count > MAX_RW_COUNT)
count = MAX_RW_COUNT;
set_fs(KERNEL_DS);
if (file->f_op->read)
ret = file->f_op->read(file, (void __user *)buf, count, pos);
else if (file->f_op->read_iter)
ret = new_sync_read(file, (void __user *)buf, count, pos);
else
ret = -EINVAL;
set_fs(old_fs);
init_sync_kiocb(&kiocb, file);
kiocb.ki_pos = *pos;
iov_iter_kvec(&iter, READ, &iov, 1, iov.iov_len);
ret = file->f_op->read_iter(&kiocb, &iter);
if (ret > 0) {
*pos = kiocb.ki_pos;
fsnotify_access(file);
add_rchar(current, ret);
}
@ -510,28 +524,31 @@ static ssize_t new_sync_write(struct file *filp, const char __user *buf, size_t
/* caller is responsible for file_start_write/file_end_write */
ssize_t __kernel_write(struct file *file, const void *buf, size_t count, loff_t *pos)
{
mm_segment_t old_fs;
const char __user *p;
struct kvec iov = {
.iov_base = (void *)buf,
.iov_len = min_t(size_t, count, MAX_RW_COUNT),
};
struct kiocb kiocb;
struct iov_iter iter;
ssize_t ret;
if (WARN_ON_ONCE(!(file->f_mode & FMODE_WRITE)))
return -EBADF;
if (!(file->f_mode & FMODE_CAN_WRITE))
return -EINVAL;
/*
* Also fail if ->write_iter and ->write are both wired up as that
* implies very convoluted semantics.
*/
if (unlikely(!file->f_op->write_iter || file->f_op->write))
return warn_unsupported(file, "write");
old_fs = get_fs();
set_fs(KERNEL_DS);
p = (__force const char __user *)buf;
if (count > MAX_RW_COUNT)
count = MAX_RW_COUNT;
if (file->f_op->write)
ret = file->f_op->write(file, p, count, pos);
else if (file->f_op->write_iter)
ret = new_sync_write(file, p, count, pos);
else
ret = -EINVAL;
set_fs(old_fs);
init_sync_kiocb(&kiocb, file);
kiocb.ki_pos = *pos;
iov_iter_kvec(&iter, WRITE, &iov, 1, iov.iov_len);
ret = file->f_op->write_iter(&kiocb, &iter);
if (ret > 0) {
*pos = kiocb.ki_pos;
fsnotify_modify(file);
add_wchar(current, ret);
}