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Commit06dbf81

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[3.13]gh-138204: Forbid expansion of a shared anonymous mmap on Linux (GH-138220) (GH-138387)
This is a Linux kernel bug which caused a bus error.https://bugzilla.kernel.org/show_bug.cgi?id=8691(cherry picked from commit33fcb0c)Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
1 parent154ec76 commit06dbf81

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3 files changed

+62
-17
lines changed

3 files changed

+62
-17
lines changed

‎Lib/test/test_mmap.py‎

Lines changed: 51 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -899,35 +899,69 @@ def test_madvise(self):
899899
self.assertEqual(m.madvise(mmap.MADV_NORMAL,0,2),None)
900900
self.assertEqual(m.madvise(mmap.MADV_NORMAL,0,size),None)
901901

902-
@unittest.skipUnless(os.name=='nt','requires Windows')
903-
deftest_resize_up_when_mapped_to_pagefile(self):
902+
deftest_resize_up_anonymous_mapping(self):
904903
"""If the mmap is backed by the pagefile ensure a resize up can happen
905904
and that the original data is still in place
906905
"""
907906
start_size=PAGESIZE
908907
new_size=2*start_size
909-
data=bytes(random.getrandbits(8)for_inrange(start_size))
908+
data=random.randbytes(start_size)
910909

911-
m=mmap.mmap(-1,start_size)
912-
m[:]=data
913-
m.resize(new_size)
914-
self.assertEqual(len(m),new_size)
915-
self.assertEqual(m[:start_size],data[:start_size])
910+
withmmap.mmap(-1,start_size)asm:
911+
m[:]=data
912+
ifsys.platform.startswith(('linux','android')):
913+
# Can't expand a shared anonymous mapping on Linux.
914+
# See https://bugzilla.kernel.org/show_bug.cgi?id=8691
915+
withself.assertRaises(ValueError):
916+
m.resize(new_size)
917+
else:
918+
try:
919+
m.resize(new_size)
920+
exceptSystemError:
921+
pass
922+
else:
923+
self.assertEqual(len(m),new_size)
924+
self.assertEqual(m[:start_size],data)
925+
self.assertEqual(m[start_size:],b'\0'* (new_size-start_size))
916926

917-
@unittest.skipUnless(os.name=='nt','requires Windows')
918-
deftest_resize_down_when_mapped_to_pagefile(self):
927+
@unittest.skipUnless(os.name=='posix','requires Posix')
928+
deftest_resize_up_private_anonymous_mapping(self):
929+
start_size=PAGESIZE
930+
new_size=2*start_size
931+
data=random.randbytes(start_size)
932+
933+
withmmap.mmap(-1,start_size,flags=mmap.MAP_PRIVATE)asm:
934+
m[:]=data
935+
try:
936+
m.resize(new_size)
937+
exceptSystemError:
938+
pass
939+
else:
940+
self.assertEqual(len(m),new_size)
941+
self.assertEqual(m[:start_size],data)
942+
self.assertEqual(m[start_size:],b'\0'* (new_size-start_size))
943+
944+
deftest_resize_down_anonymous_mapping(self):
919945
"""If the mmap is backed by the pagefile ensure a resize down up can happen
920946
and that a truncated form of the original data is still in place
921947
"""
922-
start_size=PAGESIZE
948+
start_size=2*PAGESIZE
923949
new_size=start_size//2
924-
data=bytes(random.getrandbits(8)for_inrange(start_size))
950+
data=random.randbytes(start_size)
925951

926-
m=mmap.mmap(-1,start_size)
927-
m[:]=data
928-
m.resize(new_size)
929-
self.assertEqual(len(m),new_size)
930-
self.assertEqual(m[:new_size],data[:new_size])
952+
withmmap.mmap(-1,start_size)asm:
953+
m[:]=data
954+
try:
955+
m.resize(new_size)
956+
exceptSystemError:
957+
pass
958+
else:
959+
self.assertEqual(len(m),new_size)
960+
self.assertEqual(m[:],data[:new_size])
961+
ifsys.platform.startswith(('linux','android')):
962+
# Can't expand to its original size.
963+
withself.assertRaises(ValueError):
964+
m.resize(start_size)
931965

932966
@unittest.skipUnless(os.name=='nt','requires Windows')
933967
deftest_resize_fails_if_mapping_held_elsewhere(self):
Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
1+
Forbid expansion of shared anonymous:mod:`memory maps <mmap>` on Linux,
2+
which caused a bus error.

‎Modules/mmapmodule.c‎

Lines changed: 9 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -120,6 +120,7 @@ typedef struct {
120120
#ifdefUNIX
121121
intfd;
122122
_Booltrackfd;
123+
intflags;
123124
#endif
124125

125126
PyObject*weakreflist;
@@ -871,6 +872,13 @@ mmap_resize_method(mmap_object *self,
871872
#else
872873
void*newmap;
873874

875+
#ifdef__linux__
876+
if (self->fd==-1&& !(self->flags&MAP_PRIVATE)&&new_size>self->size) {
877+
PyErr_Format(PyExc_ValueError,
878+
"mmap: can't expand a shared anonymous mapping on Linux");
879+
returnNULL;
880+
}
881+
#endif
874882
if (self->fd!=-1&&ftruncate(self->fd,self->offset+new_size)==-1) {
875883
PyErr_SetFromErrno(PyExc_OSError);
876884
returnNULL;
@@ -1651,6 +1659,7 @@ new_mmap_object(PyTypeObject *type, PyObject *args, PyObject *kwdict)
16511659
else {
16521660
m_obj->fd=-1;
16531661
}
1662+
m_obj->flags=flags;
16541663

16551664
Py_BEGIN_ALLOW_THREADS
16561665
m_obj->data=mmap(NULL,map_size,prot,flags,fd,offset);

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