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authorRusty Russell <rusty@rustcorp.com.au>2011-01-10 16:02:03 +1030
committerRusty Russell <rusty@rustcorp.com.au>2011-01-10 16:02:03 +1030
commit1e962ba9b5808dafc0be9cc562b25e3ae068ca5d (patch)
treedffc8b4cd452ea218c135c32d5e6452be20612cf
parent87aba1fa2abc28ff06f82e30cde3fa3d991e8e18 (diff)
talloc: fixed a use after free error
(Import from SAMBA commit 6f51a1f45bf4de062cce7a562477e8140630a53d): this is the minimal fix for the problem Rusty found. I previously thought that the best fix would be to change tc->parent to be valid for all pointers, but that is expensive for realloc with large numbers of child pointers, which is much more commmon than I expected it to be.
-rw-r--r--ccan/talloc/talloc.c17
1 files changed, 16 insertions, 1 deletions
diff --git a/ccan/talloc/talloc.c b/ccan/talloc/talloc.c
index fdf8eebe..63423a50 100644
--- a/ccan/talloc/talloc.c
+++ b/ccan/talloc/talloc.c
@@ -538,13 +538,28 @@ static inline int _talloc_free(const void *ptr)
final choice is the null context. */
void *child = TC_PTR_FROM_CHUNK(tc->child);
const void *new_parent = null_context;
+ struct talloc_chunk *old_parent = NULL;
if (unlikely(tc->child->refs)) {
struct talloc_chunk *p = talloc_parent_chunk(tc->child->refs);
if (p) new_parent = TC_PTR_FROM_CHUNK(p);
}
+ /* finding the parent here is potentially quite
+ expensive, but the alternative, which is to change
+ talloc to always have a valid tc->parent pointer,
+ makes realloc more expensive where there are a
+ large number of children.
+
+ The reason we need the parent pointer here is that
+ if _talloc_free_internal() fails due to references
+ or a failing destructor we need to re-parent, but
+ the free call can invalidate the prev pointer.
+ */
+ if (new_parent == null_context && (tc->child->refs || tc->child->destructor)) {
+ old_parent = talloc_parent_chunk(ptr);
+ }
if (unlikely(_talloc_free(child) == -1)) {
if (new_parent == null_context) {
- struct talloc_chunk *p = talloc_parent_chunk(ptr);
+ struct talloc_chunk *p = old_parent;
if (p) new_parent = TC_PTR_FROM_CHUNK(p);
}
__talloc_steal(new_parent, child);