From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta1.migadu.com (out-181.mta1.migadu.com [95.215.58.181]) (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 1A1ED47CC83 for ; Fri, 5 Jun 2026 07:44:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780645446; cv=none; b=XZKlzilW/iajgm95mncShnSWm0zGR0iRKUQWL+OD5G3hGIw8H/qsSEGL9bYMrZV4UmmiTIA3j7E7sDawsfb/c+EjN06Wmx/orWI+V27tpDMvR7QUhJToRwgSwLGw7+ZPnf4Qj5cZXeIWr4wrn7bdyBfNtuQii2zAFN+WSrUMLAM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780645446; c=relaxed/simple; bh=D2xpqdrvshduZoVU8rnbKr1Iu5oyTkUiWArGFDuyJw8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=PIJrYtP+tiF/47R4ppF0y/XPckYhuCzOXNrkdFpybbYu74uzrMtgeIR3Prn01thd6dSc88m8NwPIx+lrQUUgognbLAPISx3OCE8WPK0CN9hXjHasi4EZ8R8ug6dOYKBvQCkAfeGp0zjiUikEngVXaizi8tsR08TwB8hQuBHitnY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=VewviDzU; arc=none smtp.client-ip=95.215.58.181 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="VewviDzU" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780645442; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=LcvkWMpmE6Q9kfSZCHeUxEPneHRTmz74/VUa7WoySEs=; b=VewviDzUK829S+czYkrUZ7Gl5kGSvSPmBmYVZ2BOP7CLmh6y1ESmDqejJIOgHhMyDZDVOI Cf2ZK1I2MiHMBwQp/jRlQN5mRmdfAh1WOKvqhcQ/6RWgpwz41L8/w3uhbekou/RTUyyYin 5ToKtZeVG1t6lqiOymDzZT1s5WOZdok= Date: Fri, 5 Jun 2026 15:43:14 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v2] alloc_tag: fix use-after-free in /proc/allocinfo after module unload To: Suren Baghdasaryan Cc: Kent Overstreet , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260604065938.105991-1-hao.ge@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Hao Ge In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Hi Suren On 2026/6/5 03:24, Suren Baghdasaryan wrote: > On Thu, Jun 4, 2026 at 12:00 AM Hao Ge wrote: >> allocinfo_start() only reinitializes the codetag iterator at position 0. >> For subsequent reads (position > 0), it reuses cached iterator state from >> the previous batch. allocinfo_stop() drops mod_lock between read batches, >> which allows module unload to complete and free the module memory that the >> cached iterator still references: >> >> CPU0 (read) CPU1 (rmmod) >> ---- ---- >> allocinfo_start(pos=0) >> down_read(mod_lock) >> allocinfo_show() >> ... >> allocinfo_stop() >> up_read(mod_lock) >> codetag_unload_module() >> kfree(cmod) >> release_module_tags() >> ... >> free_mod_mem() >> allocinfo_start(pos=N) >> down_read(mod_lock) >> // reuses cached iter, skips re-init >> allocinfo_show() >> ct->filename <-- UAF >> >> After free_mod_mem() frees the module's .rodata, allocinfo_show() >> dereferences ct->filename, ct->function which point there. >> >> Save the iterator state in allocinfo_next() and resume from it in >> allocinfo_start() with codetag_next_ct(), which detects module removal >> via idr_find() returning NULL and skips to the next module. >> >> Fixes: 9f44df50fee4 ("alloc_tag: keep codetag iterator active between read()") >> Suggested-by: Suren Baghdasaryan >> Signed-off-by: Hao Ge > Acked-by: Suren Baghdasaryan > > Thanks! > >> --- >> v2: >> - save the iterator state in allocinfo_next() and resume from it in >> allocinfo_start() with codetag_next_ct(), which detects module removal >> via idr_find() returning NULL and skips to the next module (Suggested >> by Suren). >> v1 link: https://lore.kernel.org/all/20260525072117.112779-1-hao.ge@linux.dev/ >> --- >> lib/alloc_tag.c | 9 +++++++-- >> 1 file changed, 7 insertions(+), 2 deletions(-) >> >> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c >> index f2f574bcf383..551cc14bb1fd 100644 >> --- a/lib/alloc_tag.c >> +++ b/lib/alloc_tag.c >> @@ -45,6 +45,7 @@ int alloc_tag_ref_offs; >> >> struct allocinfo_private { >> struct codetag_iterator iter; >> + struct codetag_iterator reported_iter; > nit: I would call it maybe prev_iter since it's not yet reported (you > store it in the allocinfo_next(), not in allocinfo_show()) but that's > a minor detail. I see... >> bool print_header; >> }; >> >> @@ -58,16 +59,20 @@ static void *allocinfo_start(struct seq_file *m, loff_t *pos) >> if (node == 0) { >> priv->print_header = true; >> priv->iter = codetag_get_ct_iter(alloc_tag_cttype); >> - codetag_next_ct(&priv->iter); >> + } else { >> + priv->iter = priv->reported_iter; >> } >> + codetag_next_ct(&priv->iter); >> return priv->iter.ct ? priv : NULL; >> } >> >> static void *allocinfo_next(struct seq_file *m, void *arg, loff_t *pos) >> { >> struct allocinfo_private *priv = (struct allocinfo_private *)arg; >> - struct codetag *ct = codetag_next_ct(&priv->iter); >> + struct codetag *ct; >> >> + priv->reported_iter = priv->iter; >> + ct = codetag_next_ct(&priv->iter); AFAIK, in the seq_file call flow (start -> show -> next -> show -> next -> ...): start(0): iter = get_ct_iter(); next_ct() -> iter.ct = A show():   dump entry with iter.ct = A next():   reported_iter = iter(A); next_ct() -> iter.ct = B show():   dump entry with iter.ct = B next():   reported_iter = iter(B); next_ct() -> iter.ct = C show():   dump entry with iter.ct = C The same holds for the overflow case in the Fill loop: next():   reported_iter = iter(C); next_ct() -> iter.ct = D show():   overflow, output rolled back, break stop() on the next read: start():  iter = reported_iter(C); next_ct() -> iter.ct = D show():   dump entry with iter.ct = D So reported_iter always points to the last element that has been shown to the user. I'm fine with prev_iter as well,  What do you think? Thanks Best Regards Hao >> (*pos)++; >> if (!ct) >> return NULL; >> -- >> 2.25.1 >>