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b=pomsCqr1yF5C/tYG71y0u5knBxZDPNu8jOtVIz8EULIbQ/BnIhYMFquAqfIrBrsmc uiSK8toywvsJI50TlUAzEtP7y0pAzGCHCmUGtSPbT9TMpiimgZoeE/XQeXFfXM4ZvM ndVypsrEmtwcqpdA9QHaU98HU4WcWzvFwmot2DDK/S1NFfB/VYi1eKrE3vcQDI2AF4 W6ebe39N0NmhMT07OvfcPrLMVDL85n0ArqhBszKLldyuDEr6RqdppAwphxSA8isIrW gu8YiLT7b4/1+I68ihHiTS4wBxvnWppLdQC3TBU1vmQoAUA28ofVWRGR/+WdH7f5Xn koRpV4sM6CnGQ== From: SeongJae Park To: Cc: SeongJae Park , "# 6 . 19 . x" , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Junxi Qian Subject: [RFC PATCH 2/2] mm/damon/sysfs-schemes: protect path kfree() with damon_sysfs_lock Date: Wed, 22 Apr 2026 07:35:01 -0700 Message-ID: <20260422143503.71357-3-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260422143503.71357-1-sj@kernel.org> References: <20260422143503.71357-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: D1DF214000E X-Stat-Signature: 9eogx3ospxk9cc9taipm6uck6p6j6qbu X-HE-Tag: 1776868509-36615 X-HE-Meta: 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 0rLJMAdy 1AqxBvT7wKhNwnUuFyed08TL7rPGYXXPGhkeQ69SG8o1kSdpSR9VOiXS/BLi/arNmLnG1ln5Ta8tkgJvvDyX+zo4LRS8Dji3UGMW4UTQ3dtSlJjGJPx/sMlwYpaU5B4iatOFlpJGjX3QPsGBREFfeQwF4Dna3M/wwC+6uebesmVZTj4LGwMTnLPqIK585BsCIEzTcGdH+pEo6giWnluyIx+RywRqDksj7RadJSdHAgPZ++jMccWx/a65P+/4q85xL9LNYtG92LARsX/v3Se4Shb9AE8uldD2hizcjeiDc/u7u7rJP/pQiuZNMkQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: damon_sysfs_quot_goal->path can be read and written by users, via DAMON sysfs memcg_path file. It can also be indirectly read, for the parameters {on,off}line committing to DAMON. The reads for parameters committing are protected by damon_sysfs_lock to avoid the sysfs files being destroyed while any of the parameters are being read. But the user-driven direct reads and writes are not protected by any lock, while the write is deallocating the path-pointing buffer. As a result, the readers could read the already freed buffer (user-after-free). Note that the user-reads don't race when the same open file is used by the writer, due to kernfs's open file locking. Nonetheless, doing the reads and writes with separate open files would be common. Fix it by protecting both the user-direct reads and writes with damon_sysfs_lock. Fixes: c41e253a411e ("mm/damon/sysfs-schemes: implement path file under quota goal directory") Cc: # 6.19.x Co-developed-by: Junxi Qian Signed-off-by: Junxi Qian Signed-off-by: SeongJae Park --- mm/damon/sysfs-schemes.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c index 8d32a20531d49..245d63808411a 100644 --- a/mm/damon/sysfs-schemes.c +++ b/mm/damon/sysfs-schemes.c @@ -1197,8 +1197,13 @@ static ssize_t path_show(struct kobject *kobj, { struct damos_sysfs_quota_goal *goal = container_of(kobj, struct damos_sysfs_quota_goal, kobj); + int len; - return sysfs_emit(buf, "%s\n", goal->path ? goal->path : ""); + if (!mutex_trylock(&damon_sysfs_lock)) + return -EBUSY; + len = sysfs_emit(buf, "%s\n", goal->path ? goal->path : ""); + mutex_unlock(&damon_sysfs_lock); + return len; } static ssize_t path_store(struct kobject *kobj, @@ -1213,8 +1218,13 @@ static ssize_t path_store(struct kobject *kobj, return -ENOMEM; strscpy(path, buf, count + 1); + if (!mutex_trylock(&damon_sysfs_lock)) { + kfree(path); + return -EBUSY; + } kfree(goal->path); goal->path = path; + mutex_unlock(&damon_sysfs_lock); return count; } -- 2.47.3