From: Stefan Hajnoczi Date: Fri, 30 Sep 2011 10:39:11 +0000 (+0100) Subject: qed: fix use-after-free during l2 cache commit X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=e4fc8781db7c49b0c5ac5d24762e17c59dfe0871;p=qemu.git qed: fix use-after-free during l2 cache commit QED's metadata caching strategy allows two parallel requests to race for metadata lookup. The first one to complete will populate the metadata cache and the second one will drop the data it just read in favor of the cached data. There is a use-after-free in qed_read_l2_table_cb() and qed_commit_l2_update() where l2_table->offset was used after the l2_table may have been freed due to a metadata lookup race. Fix this by keeping the l2_offset in a local variable and not reaching into the possibly freed l2_table. Reported-by: Amit Shah Signed-off-by: Stefan Hajnoczi Signed-off-by: Anthony Liguori --- diff --git a/block/qed-table.c b/block/qed-table.c index d96afa81d7..f31f9ff069 100644 --- a/block/qed-table.c +++ b/block/qed-table.c @@ -222,21 +222,21 @@ static void qed_read_l2_table_cb(void *opaque, int ret) QEDRequest *request = read_l2_table_cb->request; BDRVQEDState *s = read_l2_table_cb->s; CachedL2Table *l2_table = request->l2_table; + uint64_t l2_offset = read_l2_table_cb->l2_offset; if (ret) { /* can't trust loaded L2 table anymore */ qed_unref_l2_cache_entry(l2_table); request->l2_table = NULL; } else { - l2_table->offset = read_l2_table_cb->l2_offset; + l2_table->offset = l2_offset; qed_commit_l2_cache_entry(&s->l2_cache, l2_table); /* This is guaranteed to succeed because we just committed the entry * to the cache. */ - request->l2_table = qed_find_l2_cache_entry(&s->l2_cache, - l2_table->offset); + request->l2_table = qed_find_l2_cache_entry(&s->l2_cache, l2_offset); assert(request->l2_table != NULL); } diff --git a/block/qed.c b/block/qed.c index 624e261b35..e87dc4decf 100644 --- a/block/qed.c +++ b/block/qed.c @@ -911,14 +911,14 @@ static void qed_commit_l2_update(void *opaque, int ret) QEDAIOCB *acb = opaque; BDRVQEDState *s = acb_to_s(acb); CachedL2Table *l2_table = acb->request.l2_table; + uint64_t l2_offset = l2_table->offset; qed_commit_l2_cache_entry(&s->l2_cache, l2_table); /* This is guaranteed to succeed because we just committed the entry to the * cache. */ - acb->request.l2_table = qed_find_l2_cache_entry(&s->l2_cache, - l2_table->offset); + acb->request.l2_table = qed_find_l2_cache_entry(&s->l2_cache, l2_offset); assert(acb->request.l2_table != NULL); qed_aio_next_io(opaque, ret);