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author | Rusty Russell <rusty@rustcorp.com.au> | 2011-01-10 16:02:03 +1030 |
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committer | Rusty Russell <rusty@rustcorp.com.au> | 2011-01-10 16:02:03 +1030 |
commit | 1e962ba9b5808dafc0be9cc562b25e3ae068ca5d (patch) | |
tree | dffc8b4cd452ea218c135c32d5e6452be20612cf | |
parent | 87aba1fa2abc28ff06f82e30cde3fa3d991e8e18 (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.c | 17 |
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); |