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(223.70.159.239) by smtp.migadu.com with ESMTPS id 0453194cf996fbf3; Mon, 17 Aug 2026 04:27:25 +0000 X-Migadu-Flow: FLOW_OUT From: Tao Cui To: akpm@linux-foundation.org Cc: linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, cui.tao@linux.dev, Tao Cui Subject: [PATCH] mm: page_counter: reject empty string in page_counter_memparse() Date: Mon, 17 Aug 2026 12:26:52 +0800 Message-ID: <20260817042652.74136-1-cui.tao@linux.dev> X-Mailer: git-send-email 2.43.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: C9DAB80004 X-Stat-Signature: czq6wn17fq8ps3dmxrwn7cxcjokrn7pg X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1786940849-292487 X-HE-Meta: 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 2jPbB+UJ HiMWWMfFPKaY9IAQf96YMER5O/RghiDdlWlkyYvp8uQeemr6UpN/3+bF3m6Rsax1jCj0/XqJMVjELVwfCEfnBmDyt8QCX1oSBMcGGnFnHg4WN4yXCWLzT866xfAcHPFjvUqIEVQJtmlOROhigLVlVeqpZDpDgk0a7j8a/xtZ1S4FFQ0n2AGBT8ga0vQM3o/NmWPHB4hSM6laSadKa3qVdB8DIrA4r5kY6g8PbJxKutNyUQKz/Lm0djd++nC7ztuJqiQfww0EuqL4g2/TWMO4GQEFAJA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Tao Cui memparse() consumes no characters on an empty input and leaves the end pointer at the terminating NUL. The only validation in page_counter_memparse() checks for trailing characters, so an empty input slips through and the limit becomes 0. All limit write callbacks of the memory controller strstrip() the input before calling this helper, so a script that writes an unset variable hits this path: LIMIT= echo "$LIMIT" > $CG/memory.max echo $? 0 cat $CG/memory.max 0 Nothing reports the mistake: the limit is now 0 and the OOM killer goes after every task in the cgroup. The same happens for memory.min, memory.low, memory.high, memory.swap.high, memory.swap.max and memory.zswap.max, where 0 silently removes the protection or disables swap and zswap. Reject the input when no characters were consumed, which is the one case the trailing-character check cannot catch. Fixes: 3e32cb2e0a12 ("mm: memcontrol: lockless page counters") Signed-off-by: Tao Cui --- mm/page_counter.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/page_counter.c b/mm/page_counter.c index 661e0f2a5127..d14db705b04f 100644 --- a/mm/page_counter.c +++ b/mm/page_counter.c @@ -281,7 +281,7 @@ int page_counter_memparse(const char *buf, const char *max, } bytes = memparse(buf, &end); - if (*end != '\0') + if (*end != '\0' || end == buf) return -EINVAL; *nr_pages = min(bytes / PAGE_SIZE, (u64)PAGE_COUNTER_MAX); -- 2.43.0