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libbpf, hashmap: Fix undefined behavior in hash_bits

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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: e3b9242240 ("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
This commit is contained in:
Ian Rogers 2020-10-29 15:37:07 -07:00 committed by Daniel Borkmann
parent 080b6f4076
commit 7a078d2d18
1 changed files with 9 additions and 6 deletions
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15
tools/lib/bpf/hashmap.h
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@ -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);
@ -174,17 +177,17 @@ 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))