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WasmFS: enforce open file access mode on read/write #260

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Merged
pavelsavara merged 2 commits into from
Jul 8, 2026
Merged

WasmFS: enforce open file access mode on read/write #260

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WasmFS: enforce open file access mode on read/write
pavelsavara Jul 3, 2026
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pavelsavara Jul 7, 2026
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18 changes: 13 additions & 5 deletions system/lib/wasmfs/syscalls.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -112,6 +112,12 @@ static __wasi_errno_t writeAtOffset(OffsetHandling setOffset,
return __WASI_ERRNO_ISDIR;
}

// A file opened for reading only (O_RDONLY) cannot be written. POSIX write(2)
// returns EBADF when the file descriptor is not open for writing.
if ((lockedOpenFile.getFlags() & O_ACCMODE) == O_RDONLY) {
return __WASI_ERRNO_BADF;
}

auto lockedFile = file->locked();

if (setOffset == OffsetHandling::OpenFileState) {
Expand All @@ -128,8 +134,6 @@ static __wasi_errno_t writeAtOffset(OffsetHandling setOffset,
}
}

// TODO: Check open file access mode for write permissions.

size_t bytesWritten = 0;
for (size_t i = 0; i < iovs_len; i++) {
const uint8_t* buf = iovs[i].buf;
Expand Down Expand Up @@ -198,15 +202,19 @@ static __wasi_errno_t readAtOffset(OffsetHandling setOffset,
return __WASI_ERRNO_INVAL;
}

// TODO: Check open file access mode for read permissions.

auto file = lockedOpenFile.getFile()->dynCast<DataFile>();

// If file is nullptr, then the file was not a DataFile.
if (!file) {
return __WASI_ERRNO_ISDIR;
}

// A file opened for writing only (O_WRONLY) cannot be read. POSIX read(2)
// returns EBADF when the file descriptor is not open for reading.
if ((lockedOpenFile.getFlags() & O_ACCMODE) == O_WRONLY) {
return __WASI_ERRNO_BADF;
}

auto lockedFile = file->locked();

size_t bytesRead = 0;
Expand Down Expand Up @@ -568,7 +576,7 @@ int wasmfs_create_file(char* pathname, mode_t mode, backend_t backend) {
static_assert(std::is_same_v<decltype(doOpen(0, 0, 0, 0)), unsigned int>,
"unexpected conversion from result of doOpen to int");
return doOpen(
path::parseParent((char*)pathname), O_CREAT | O_EXCL, mode, backend);
path::parseParent(pathname), O_CREAT | O_EXCL | O_RDWR, mode, backend);
}

// TODO: Test this with non-AT_FDCWD values.
Expand Down