From: Ian Rogers <irogers@google.com>
To: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>,
netdev@vger.kernel.org, bpf@vger.kernel.org,
linux-kernel@vger.kernel.org
Cc: Ian Rogers <irogers@google.com>
Subject: [PATCH v2] libbpf hashmap: Fix undefined behavior in hash_bits
Date: Thu, 29 Oct 2020 15:37:07 -0700 [thread overview]
Message-ID: <20201029223707.494059-1-irogers@google.com> (raw)
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.
Suggested-by: Andrii Nakryiko <andriin@fb.com>,
Signed-off-by: Ian Rogers <irogers@google.com>
---
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 d9b385fe808c..10a4c4cd13cf 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);
@@ -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))
--
2.29.1.341.ge80a0c044ae-goog
next reply other threads:[~2020-10-29 22:37 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-29 22:37 Ian Rogers [this message]
2020-10-29 22:38 ` [PATCH v2] libbpf hashmap: Fix undefined behavior in hash_bits Andrii Nakryiko
2020-10-29 22:57 ` Song Liu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20201029223707.494059-1-irogers@google.com \
--to=irogers@google.com \
--cc=andriin@fb.com \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=john.fastabend@gmail.com \
--cc=kafai@fb.com \
--cc=kpsingh@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=songliubraving@fb.com \
--cc=yhs@fb.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).