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 1B74B345EB9; Tue, 11 Aug 2026 17:52:05 +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=1786470727; cv=none; b=CJCfQcSaFv/6+NXGZGqG2P5NhXQUsw7/JpOULMFCzc3GhtRfnDlveX4JPQwplxFlxq88TMKgZ+W7o5aPtxuojFRqlOmjowKzrRT5EwPRD+sqjxYxJvqElUpWaPuDqKi7J9mOgWusrdFC1jYTuBPWFP3lVoDrUBSR6sPanjYJ18k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786470727; c=relaxed/simple; bh=SjsB4co41jSVoP6bnS8K970FIJHgbDqURpRb0nLHCus=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=BaKwihaS9QDGthNzK8X8sR3GvxGn/EmPSTVy8/a/2vj/IspCx7O50qgqYeQ3sUJeca/6gs9xdhYutSDYyL+VUDIo3mCG7+RRcjhny+x0aj4BVXxYV0anvfHT/Gzb7/tUrIdOITGKmtH9ElwzhXQNC7V8UswSCI47kpJjztI0F9w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eT/yQk6n; 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="eT/yQk6n" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5D9221F000E9; Tue, 11 Aug 2026 17:52:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786470725; bh=NukpYtAtFanqUbiSgiuvXq4MtL6kmbQJhHG02AimIxQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=eT/yQk6na60lRZJnHPUk4nhR646E6jDyMcfFwUUEiF8QSlcoSKqeh8mlm7JzRFH9j L4m08Oud9PlYsY/YtGPuKgkCkfwys4CUeFSilp6L7XAIfymyr9/IYWRCkw/HqX703E h7ltnIdcsLLCxWqyO6PF4b7lLFlserdFQumelHjBF2/C/jYGmzksMpXw2yZnwsdVnK lN74MSTx3zVsIjXc+RzUEUWfEGWDd5lF58sdJYn3tyYKeVdeFT+qsdbTJg6v4wvHNR hgUp3vimU7M7ax8Jn847x1/7Ee92oIribuZ7EOS5J4KHCELvnJwBX+HTgjB0/IWI2m z4DX1rLwI9IYA== 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: Tue, 11 Aug 2026 14:51:33 -0300 Message-ID: <20260811175140.7235-5-acme@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260811175140.7235-1-acme@kernel.org> References: <20260811175140.7235-1-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 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 32ae5c78cdb906e6..8e16b919e80721f0 100644 --- a/tools/perf/util/dso.c +++ b/tools/perf/util/dso.c @@ -1005,7 +1005,20 @@ 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