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authorMatthew Wilcox <mawilcox@microsoft.com>2017-03-03 12:16:10 -0500
committerMatthew Wilcox <mawilcox@microsoft.com>2017-03-07 13:18:23 -0500
commit4ecd9542dbc3e07f3bd3870aac12839f72b47db4 (patch)
tree1345c7ca57563006a0355bec1bbe689dd14ca67c /lib
parent3f1b6f9d49ba5a209d745fa2448657d8b66ed0c0 (diff)
ida: Free correct IDA bitmap
There's a relatively rare race where we look at the per-cpu preallocated IDA bitmap, see it's NULL, allocate a new one, and atomically update it. If the kmalloc() happened to sleep and we were rescheduled to a different CPU, or an interrupt came in at the exact right time, another task might have successfully allocated a bitmap and already deposited it. I forgot what the semantics of cmpxchg() were and ended up freeing the wrong bitmap leading to KASAN reporting a use-after-free. Dmitry found the bug with syzkaller & wrote the patch. I wrote the test case that will reproduce the bug without his patch being applied. Reported-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Diffstat (limited to 'lib')
-rw-r--r--lib/radix-tree.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 5ed506d648c4..691a9ad48497 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -2129,8 +2129,8 @@ int ida_pre_get(struct ida *ida, gfp_t gfp)
struct ida_bitmap *bitmap = kmalloc(sizeof(*bitmap), gfp);
if (!bitmap)
return 0;
- bitmap = this_cpu_cmpxchg(ida_bitmap, NULL, bitmap);
- kfree(bitmap);
+ if (this_cpu_cmpxchg(ida_bitmap, NULL, bitmap))
+ kfree(bitmap);
}
return 1;