https://github.com/python/cpython/commit/26800cf25a0970d46934fa9a881c0ef6881d642b
commit: 26800cf25a0970d46934fa9a881c0ef6881d642b
branch: main
author: 6t8k <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2024-02-17T11:16:06Z
summary:
gh-95782: Fix io.BufferedReader.tell() etc. being able to return offsets < 0
(GH-99709)
lseek() always returns 0 for character pseudo-devices like
`/dev/urandom` (for other non-regular files, e.g. `/dev/stdin`, it
always returns -1, to which CPython reacts by raising appropriate
exceptions). They are thus technically seekable despite not having seek
semantics.
When calling read() on e.g. an instance of `io.BufferedReader` that
wraps such a file, `BufferedReader` reads ahead, filling its buffer,
creating a discrepancy between the number of bytes read and the internal
`tell()` always returning 0, which previously resulted in e.g.
`BufferedReader.tell()` or `BufferedReader.seek()` being able to return
positions < 0 even though these are supposed to be always >= 0.
Invariably keep the return value non-negative by returning
max(former_return_value, 0) instead, and add some corresponding tests.
files:
A Misc/NEWS.d/next/Library/2022-11-22-23-17-43.gh-issue-95782.an_and.rst
M Lib/_pyio.py
M Lib/test/test_io.py
M Modules/_io/bufferedio.c
diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 8a0d0dc4b1a0b8..a3fede699218a1 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -1197,7 +1197,8 @@ def _readinto(self, buf, read1):
return written
def tell(self):
- return _BufferedIOMixin.tell(self) - len(self._read_buf) +
self._read_pos
+ # GH-95782: Keep return value non-negative
+ return max(_BufferedIOMixin.tell(self) - len(self._read_buf) +
self._read_pos, 0)
def seek(self, pos, whence=0):
if whence not in valid_seek_flags:
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index cc387afa391909..5491c0575dbd3f 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -257,6 +257,27 @@ class PyMockUnseekableIO(MockUnseekableIO, pyio.BytesIO):
UnsupportedOperation = pyio.UnsupportedOperation
+class MockCharPseudoDevFileIO(MockFileIO):
+ # GH-95782
+ # ftruncate() does not work on these special files (and CPython then raises
+ # appropriate exceptions), so truncate() does not have to be accounted for
+ # here.
+ def __init__(self, data):
+ super().__init__(data)
+
+ def seek(self, *args):
+ return 0
+
+ def tell(self, *args):
+ return 0
+
+class CMockCharPseudoDevFileIO(MockCharPseudoDevFileIO, io.BytesIO):
+ pass
+
+class PyMockCharPseudoDevFileIO(MockCharPseudoDevFileIO, pyio.BytesIO):
+ pass
+
+
class MockNonBlockWriterIO:
def __init__(self):
@@ -1648,6 +1669,30 @@ def test_truncate_on_read_only(self):
self.assertRaises(self.UnsupportedOperation, bufio.truncate)
self.assertRaises(self.UnsupportedOperation, bufio.truncate, 0)
+ def test_tell_character_device_file(self):
+ # GH-95782
+ # For the (former) bug in BufferedIO to manifest, the wrapped IO obj
+ # must be able to produce at least 2 bytes.
+ raw = self.MockCharPseudoDevFileIO(b"12")
+ buf = self.tp(raw)
+ self.assertEqual(buf.tell(), 0)
+ self.assertEqual(buf.read(1), b"1")
+ self.assertEqual(buf.tell(), 0)
+
+ def test_seek_character_device_file(self):
+ raw = self.MockCharPseudoDevFileIO(b"12")
+ buf = self.tp(raw)
+ self.assertEqual(buf.seek(0, io.SEEK_CUR), 0)
+ self.assertEqual(buf.seek(1, io.SEEK_SET), 0)
+ self.assertEqual(buf.seek(0, io.SEEK_CUR), 0)
+ self.assertEqual(buf.read(1), b"1")
+
+ # In the C implementation, tell() sets the BufferedIO's abs_pos to 0,
+ # which means that the next seek() could return a negative offset if it
+ # does not sanity-check:
+ self.assertEqual(buf.tell(), 0)
+ self.assertEqual(buf.seek(0, io.SEEK_CUR), 0)
+
class CBufferedReaderTest(BufferedReaderTest, SizeofTest):
tp = io.BufferedReader
@@ -4880,7 +4925,7 @@ def load_tests(loader, tests, pattern):
# classes in the __dict__ of each test.
mocks = (MockRawIO, MisbehavedRawIO, MockFileIO, CloseFailureIO,
MockNonBlockWriterIO, MockUnseekableIO, MockRawIOWithoutRead,
- SlowFlushRawIO)
+ SlowFlushRawIO, MockCharPseudoDevFileIO)
all_members = io.__all__
c_io_ns = {name : getattr(io, name) for name in all_members}
py_io_ns = {name : getattr(pyio, name) for name in all_members}
diff --git
a/Misc/NEWS.d/next/Library/2022-11-22-23-17-43.gh-issue-95782.an_and.rst
b/Misc/NEWS.d/next/Library/2022-11-22-23-17-43.gh-issue-95782.an_and.rst
new file mode 100644
index 00000000000000..123c3944aa3a3a
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-11-22-23-17-43.gh-issue-95782.an_and.rst
@@ -0,0 +1,4 @@
+Fix :func:`io.BufferedReader.tell`, :func:`io.BufferedReader.seek`,
+:func:`_pyio.BufferedReader.tell`, :func:`io.BufferedRandom.tell`,
+:func:`io.BufferedRandom.seek` and :func:`_pyio.BufferedRandom.tell`
+being able to return negative offsets.
diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
index 8ebe9ec7095586..b3450eeaf99401 100644
--- a/Modules/_io/bufferedio.c
+++ b/Modules/_io/bufferedio.c
@@ -1325,7 +1325,11 @@ _io__Buffered_tell_impl(buffered *self)
if (pos == -1)
return NULL;
pos -= RAW_OFFSET(self);
- /* TODO: sanity check (pos >= 0) */
+
+ // GH-95782
+ if (pos < 0)
+ pos = 0;
+
return PyLong_FromOff_t(pos);
}
@@ -1395,6 +1399,11 @@ _io__Buffered_seek_impl(buffered *self, PyObject
*targetobj, int whence)
offset = target;
if (offset >= -self->pos && offset <= avail) {
self->pos += offset;
+
+ // GH-95782
+ if (current - avail + offset < 0)
+ return PyLong_FromOff_t(0);
+
return PyLong_FromOff_t(current - avail + offset);
}
}
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