[PATCH 5.9 133/255] libbpf, hashmap: Fix undefined behavior in hash_bits

Greg Kroah-Hartman
2020-11-17T13:38:44Z

From: Ian Rogers <irogers@google.com>

[ Upstream commit 7a078d2d18801bba7bde7337a823d7342299acf7 ]

If bits is 0, the case when the map is empty, then the >> is the size of
the register which is undefined behavior - on x86 it is the same as a
shift by 0.

Fix by handling the 0 case explicitly and guarding calls to hash_bits for
empty maps in hashmap__for_each_key_entry and hashmap__for_each_entry_safe.

Fixes: e3b924224028 ("libbpf: add resizable non-thread safe internal hashmap")
Suggested-by: Andrii Nakryiko <andriin@fb.com>,
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20201029223707.494059-1-irogers@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/lib/bpf/hashmap.h | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h
index e0af36b0e5d83..6a3c3d8bb4ab8 100644
--- a/tools/lib/bpf/hashmap.h
+++ b/tools/lib/bpf/hashmap.h
@@ -15,6 +15,9 @@
static inline size_t hash_bits(size_t h, int bits)
{
/* shuffle bits and return requested number of upper bits */
+ if (bits == 0)
+ return 0;
+
#if (__SIZEOF_SIZE_T__ == __SIZEOF_LONG_LONG__)
/* LP64 case */
return (h * 11400714819323198485llu) >> (__SIZEOF_LONG_LONG__ * 8 - bits);
@@ -162,17 +165,17 @@ bool hashmap__find(const struct hashmap *map, const void *key, void **value);
* @key: key to iterate entries for
*/
#define hashmap__for_each_key_entry(map, cur, _key) \
- for (cur = ({ size_t bkt = hash_bits(map->hash_fn((_key), map->ctx),\
- map->cap_bits); \
- map->buckets ? map->buckets[bkt] : NULL; }); \
+ for (cur = map->buckets \
+ ? map->buckets[hash_bits(map->hash_fn((_key), map->ctx), map->cap_bits)] \
+ : NULL; \
cur; \
cur = cur->next) \
if (map->equal_fn(cur->key, (_key), map->ctx))

#define hashmap__for_each_key_entry_safe(map, cur, tmp, _key) \
- for (cur = ({ size_t bkt = hash_bits(map->hash_fn((_key), map->ctx),\
- map->cap_bits); \
- cur = map->buckets ? map->buckets[bkt] : NULL; }); \
+ for (cur = map->buckets \
+ ? map->buckets[hash_bits(map->hash_fn((_key), map->ctx), map->cap_bits)] \
+ : NULL; \
cur && ({ tmp = cur->next; true; }); \
cur = tmp) \
if (map->equal_fn(cur->key, (_key), map->ctx))
--
2.27.0