[PATCH] fs:change uiomove() to use size_t in the signature instead of int

[Waldemar Kozaczuk]

As Wonsup Yoon reported in the issue #1095 following C++ trying
to read large number of bytes from /dev/random fails:

```
#include<fstream>
#include<vector>
#include<iostream>

#define READ_BYTES (1LL << 31)

int main(){

std::ifstream file("/dev/urandom");

std::vector<char> data(READ_BYTES);
data[0] = 1;
file.read(data.data(), READ_BYTES);

std::cout << +data[0] << std::endl;


return 0;
}
```

To make long story short (see the issue for more details)
it turns out that the culprit is wron signature of uiomove()
function that uses int instead of size_t for n parameter.
This patch fixes it.

Fixes #1095

Signed-off-by: Waldemar Kozaczuk <jwkoz...@gmail.com>
---
fs/vfs/subr_uio.cc | 4 ++--
include/osv/uio.h | 8 ++------
2 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/fs/vfs/subr_uio.cc b/fs/vfs/subr_uio.cc
index bf138b8e..fdc89bd4 100644
--- a/fs/vfs/subr_uio.cc
+++ b/fs/vfs/subr_uio.cc
@@ -41,13 +41,13 @@
#include <osv/uio.h>

int
-uiomove(void *cp, int n, struct uio *uio)
+uiomove(void *cp, size_t n, struct uio *uio)
{
assert(uio->uio_rw == UIO_READ || uio->uio_rw == UIO_WRITE);

while (n > 0 && uio->uio_resid) {
struct iovec *iov = uio->uio_iov;
- int cnt = iov->iov_len;
+ size_t cnt = iov->iov_len;
if (cnt == 0) {
uio->uio_iov++;
uio->uio_iovcnt--;
diff --git a/include/osv/uio.h b/include/osv/uio.h
index 8e2951be..2c117e7c 100644
--- a/include/osv/uio.h
+++ b/include/osv/uio.h
@@ -42,11 +42,7 @@ __BEGIN_DECLS

enum uio_rw { UIO_READ, UIO_WRITE };

-/*
- * Safe default to prevent possible overflows in user code, otherwise could
- * be SSIZE_T_MAX.
- */
-#define IOSIZE_MAX INT_MAX
+#define IOSIZE_MAX SSIZE_MAX

#undef UIO_MAXIOV
#define UIO_MAXIOV 1024
@@ -61,7 +57,7 @@ struct uio {
enum uio_rw uio_rw; /* operation */
};

-int uiomove(void *cp, int n, struct uio *uio);
+int uiomove(void *cp, size_t n, struct uio *uio);

__END_DECLS

--
2.26.2

[Wonsup Yoon]

Yes, it is fixed.

2020년 8월 18일 화요일 오전 1시 0분 23초 UTC+9에 jwkoz...@gmail.com님이 작성:

[Commit Bot]

From: Waldemar Kozaczuk <jwkoz...@gmail.com>
Committer: Waldemar Kozaczuk <jwkoz...@gmail.com>
Branch: master

fs:change uiomove() to use size_t in the signature instead of int

As Wonsup Yoon reported in the issue #1095 following C++ trying
to read large number of bytes from /dev/random fails:

```
#include<fstream>
#include<vector>
#include<iostream>

#define READ_BYTES (1LL << 31)

int main(){

std::ifstream file("/dev/urandom");

std::vector<char> data(READ_BYTES);
data[0] = 1;
file.read(data.data(), READ_BYTES);

std::cout << +data[0] << std::endl;

return 0;
}
```

To make long story short (see the issue for more details)
it turns out that the culprit is wron signature of uiomove()
function that uses int instead of size_t for n parameter.
This patch fixes it.

Fixes #1095

Signed-off-by: Waldemar Kozaczuk <jwkoz...@gmail.com>

---

diff --git a/fs/vfs/subr_uio.cc b/fs/vfs/subr_uio.cc

--- a/fs/vfs/subr_uio.cc
+++ b/fs/vfs/subr_uio.cc
@@ -41,13 +41,13 @@
#include <osv/uio.h>

int
-uiomove(void *cp, int n, struct uio *uio)
+uiomove(void *cp, size_t n, struct uio *uio)
{
assert(uio->uio_rw == UIO_READ || uio->uio_rw == UIO_WRITE);

while (n > 0 && uio->uio_resid) {
struct iovec *iov = uio->uio_iov;
- int cnt = iov->iov_len;
+ size_t cnt = iov->iov_len;
if (cnt == 0) {
uio->uio_iov++;
uio->uio_iovcnt--;
diff --git a/include/osv/uio.h b/include/osv/uio.h

[Nadav Har'El]

Thanks. Looks good.

I agree that using SSIZE_MAX as the maximum instead of SIZE_MAX (which you could have used) is indeed a good idea - it will prevent somebody from accidentally storing a large number in a small integer and then having it wrongly sign-extended, e.g.,

          

     int x = 4294967295 // looks like a large number, but gets treated as "-1".

     uiomove(..., x)        // x sign extended to 64-bit "-1", i.e., 18446744073709551616, will refuse to work because > SSIZE_MAX, so good.

--
Nadav Har'El

n...@scylladb.com

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