From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D45D9485CDC; Thu, 13 Aug 2026 15:12:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786633930; cv=none; b=Z23uedFx04RAsCbjjgU9vI/g8A/h0VyYQG4IPc139TX1EXpVy9RLvWNojRb1TQ2AkMlOP6Yrnbv17AsvOpBowl7FaO0kv1HSc14mTQWuqhqHqUIMe1HFTmJYObAn8+7VyPJVNXbBgfzw1FzMVNe6lrBz9FIrUd31kVHiDniitrA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786633930; c=relaxed/simple; bh=w/ov9dTFWUJ5efYR6riEWce9i1ZpojtqDWXcbEGZqcg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=eC0CeV8hBlWq8cAkPx6ueZO1hlcB1KYlaHpgGgLqKsYCC8a63sU11YbtN9lMiaPWgJutRtazZV0cb0YGcbpGVncTWlHlQPiEDSsUEI6rQ8bS3K88cMBcRPxz/7b/3fGnjWjt1Y/6mqFmtgQGB6wpEKghnwlre8vyYim3YHvQSXM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NX7bAYfB; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="NX7bAYfB" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7B99E1F00A3A; Thu, 13 Aug 2026 15:12:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786633928; bh=5RWhhoRAyfdFS4j/kY6A9DoZiJijxrHc7BxW9IrX+yA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=NX7bAYfBgiFp6ScuK4KuFRVEblVxaDgcq+S/cIgG6yTakkl1AwBjNiTq8NwSm9gwj lyXhbKZvAv+Bt1G3Ecgp+xLWstHbllLzJDONsGRhJZgv8Eo9PJc1MVk8MlG2CkCa27 avp4Y0PbR2RheLmIaQ5eNJF5Rthn0UWqp+24v8u2+MSlFDJPJfQsHWGWyjP/Nje34N sYa7Zmtl9W+1RN0Dtgg/T4pbr3FijTBC24plNfxURo6T8q/s1OZTNFNDrXmmmQ9/UE 6bhmFmm9lgKrsE/peFdCNrW4x72SojX1ShADLEyfV/w8ozwk/RNib5GAVG824iGaXs 0uxGT3l/l8Llw== From: Arnaldo Carvalho de Melo To: Namhyung Kim Cc: Ingo Molnar , Thomas Gleixner , James Clark , Jiri Olsa , Ian Rogers , Adrian Hunter , Clark Williams , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Arnaldo Carvalho de Melo , sashiko-bot Subject: [PATCH 4/5] perf dso: Guard against cache underflow on short reads in dso_cache__memcpy() Date: Thu, 13 Aug 2026 12:11:45 -0300 Message-ID: <20260813151148.23169-5-acme@kernel.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260813151148.23169-1-acme@kernel.org> References: <20260813151148.23169-1-acme@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Arnaldo Carvalho de Melo dso_cache__memcpy() computes cache_offset = offset - cache->offset, then cache_size = min(cache->size - cache_offset, size). The RB tree lookup in __dso_cache__find() matches using the full DSO__DATA_CACHE_SIZE window, but cache->size reflects the actual pread return value from dso_cache__populate(). A short pread (e.g. near end-of-file) makes cache->size smaller than DSO__DATA_CACHE_SIZE. If a subsequent access targets an offset past cache->offset + cache->size but within the DSO__DATA_CACHE_SIZE window, the cache entry is found but cache_offset exceeds cache->size. Since both are u64, the subtraction cache->size - cache_offset wraps to a large value, min() selects the caller's size, and memcpy reads out of bounds. Return 0 for an offset past the valid cached data. For a regular file a short pread only happens at end-of-file, so 0 is what a direct pread() at that offset would return: cached_io() stops its read loop as on EOF. Re-reading from the backing file would not help — a second pread at the same offset returns the same short count. Fixes: 366df72657e0 ("perf dso: Refactor dso_cache__read()") Reported-by: sashiko-bot Reviewed-by: Ian Rogers Cc: Adrian Hunter Assisted-by: Claude:claude-opus-4.6 Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/dso.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c index 60aa77f7978514ec..4dd64069c4348c06 100644 --- a/tools/perf/util/dso.c +++ b/tools/perf/util/dso.c @@ -1014,7 +1014,20 @@ static ssize_t dso_cache__memcpy(struct dso_cache *cache, u64 offset, u8 *data, u64 size, bool out) { u64 cache_offset = offset - cache->offset; - u64 cache_size = min(cache->size - cache_offset, size); + u64 cache_size; + + /* + * The RB tree matches using DSO__DATA_CACHE_SIZE, but a short + * pread may leave cache->size smaller. For a regular file a + * short pread only happens at end-of-file, so an offset past + * the valid data is EOF: return 0, matching what a direct + * pread() at that offset would return, and cached_io() then + * stops its read loop. + */ + if (cache_offset >= cache->size) + return 0; + + cache_size = min(cache->size - cache_offset, size); if (out) memcpy(data, cache->data + cache_offset, cache_size); -- 2.55.0