Re: iov_iter_fault_in_readable fix

Christoph Hellwig
2007-06-14T17:31:55Z

On Wed, Jun 13, 2007 at 05:57:59PM +0400, Dmitriy Monakhov wrote:
> Function prerform check for signgle region, with out respect to
> segment nature of iovec, For example writev no longer works :)

Btw, could someone please start to collect all sniplets like this in
a nice simple regression test suite? If no one wants to start a new
one we should probably just put it into xfsqa (which should be useable
for other filesystems aswell despite the name)

>
> /* TESTCASE BEGIN */
> #include <stdio.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <sys/uio.h>
> #include <sys/mman.h>
> #define SIZE (4096 * 2)
> int main(int argc, char* argv[])
> {
> char* ptr[4];
> struct iovec iov[2];
> int fd, ret;
> ptr[0] = mmap(NULL, SIZE, PROT_READ|PROT_WRITE,
> MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
> ptr[1] = mmap(NULL, SIZE, PROT_NONE,
> MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
> ptr[2] = mmap(NULL, SIZE, PROT_READ|PROT_WRITE,
> MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
> ptr[3] = mmap(NULL, SIZE, PROT_NONE,
> MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
>
> iov[0].iov_base = ptr[0] + (SIZE -1);
> iov[0].iov_len = 1;
> memset(ptr[0], 1, SIZE);
>
> iov[1].iov_base = ptr[2];
> iov[1].iov_len = SIZE;
> memset(ptr[2], 2, SIZE);
>
> fd = open(argv[1], O_CREAT|O_RDWR|O_TRUNC, 0666);
> ret = writev(fd, iov, sizeof(iov) / sizeof(struct iovec));
> return 0;
> }
> /* TESTCASE END*/
> We will get folowing result:
> writev(3, [{"\1", 1}, {"\2"..., 8192}], 2) = -1 EFAULT (Bad address)
>
> this is hidden bug, and it was invisiable because XXXX_fault_in_readable
> return value was ignored before. Lets iov_iter_fault_in_readable
> perform checks for all segments.
>
> Signed-off-by: Dmitriy Monakhov <dmonakhov@openvz.org>
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index fef19fc..7e025ea 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -433,7 +433,7 @@ size_t iov_iter_copy_from_user_atomic(struct page *page,
> size_t iov_iter_copy_from_user(struct page *page,
> struct iov_iter *i, unsigned long offset, size_t bytes);
> void iov_iter_advance(struct iov_iter *i, size_t bytes);
> -int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes);
> +int iov_iter_fault_in_readable(struct iov_iter *i, size_t *bytes);
> size_t iov_iter_single_seg_count(struct iov_iter *i);
>
> static inline void iov_iter_init(struct iov_iter *i,
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 8d59ed9..8600c3e 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1817,10 +1817,32 @@ void iov_iter_advance(struct iov_iter *i, size_t bytes)
> }
> EXPORT_SYMBOL(iov_iter_advance);
>
> -int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
> +int iov_iter_fault_in_readable(struct iov_iter *i, size_t* bytes)
> {
> - char __user *buf = i->iov->iov_base + i->iov_offset;
> - return fault_in_pages_readable(buf, bytes);
> + size_t len = *bytes;
> + int ret;
> + if (likely(i->nr_segs == 1)) {
> + ret = fault_in_pages_readable(i->iov->iov_base, len);
> + if (ret)
> + *bytes = 0;
> + } else {
> + const struct iovec *iov = i->iov;
> + size_t base = i->iov_offset;
> + *bytes = 0;
> + while (len) {
> + int copy = min(len, iov->iov_len - base);
> + if ((ret = fault_in_pages_readable(iov->iov_base + base, copy)))
> + break;
> + *bytes += copy;
> + len -= copy;
> + base += copy;
> + if (iov->iov_len == base) {
> + iov++;
> + base = 0;
> + }
> + }
> + }
> + return ret;
> }
> EXPORT_SYMBOL(iov_iter_fault_in_readable);
>
> @@ -2110,7 +2132,7 @@ static ssize_t generic_perform_write_2copy(struct file *file,
> * to check that the address is actually valid, when atomic
> * usercopies are used, below.
> */
> - if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
> + if (unlikely(iov_iter_fault_in_readable(i, &bytes) && !bytes)) {
> status = -EFAULT;
> break;
> }
> @@ -2284,7 +2306,7 @@ again:
> * to check that the address is actually valid, when atomic
> * usercopies are used, below.
> */
> - if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
> + if (unlikely(iov_iter_fault_in_readable(i, &bytes)&& !bytes)) {
> status = -EFAULT;
> break;
> }
>
>
> -
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