iov_iter_fault_in_readable fix

Dmitriy Monakhov
2007-06-13T10:57:34Z

Function prerform check for signgle region, with out respect to
segment nature of iovec, For example writev no longer works :)

/* 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;
}