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[2003:dc:6f4c:be00:230:64ff:fe74:809]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4983600bd6esm12209506f8f.28.2026.11.11.08.18.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Nov 2026 08:18:40 -0800 (PST) From: Max Kellermann To: xiubli@redhat.com, idryomov@gmail.com, amarkuze@redhat.com, ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Max Kellermann , stable@vger.kernel.org Subject: [PATCH 6/9] ceph: fix mdsmap use-after-free in ceph_get_tree() error path Date: Wed, 11 Nov 2026 17:18:27 +0100 Message-ID: <20261111161830.1336485-7-max.kellermann@ionos.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261111161830.1336485-1-max.kellermann@ionos.com> References: <20261111161830.1336485-1-max.kellermann@ionos.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When mounting fails, ceph_get_tree() calls ceph_mdsmap_is_cluster_available() on mdsc->mdsmap without holding mdsc->mutex. The MDS client is still running at that point, and ceph_mdsc_handle_mdsmap() can replace the mdsmap and free the old one concurrently, so this can walk freed memory. Check the map while holding mdsc->mutex. Fixes: 97820058fb28 ("ceph: check availability of mds cluster on mount after wait timeout") Cc: stable@vger.kernel.org Signed-off-by: Max Kellermann --- fs/ceph/super.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/fs/ceph/super.c b/fs/ceph/super.c index 01f92d77ef45..94ff935492e5 100644 --- a/fs/ceph/super.c +++ b/fs/ceph/super.c @@ -1364,6 +1364,7 @@ static int ceph_get_tree(struct fs_context *fc) struct dentry *res; int (*compare_super)(struct super_block *, struct fs_context *) = ceph_compare_super; + bool available; int err; dout("ceph_get_tree\n"); @@ -1429,7 +1430,11 @@ static int ceph_get_tree(struct fs_context *fc) return 0; out_splat: - if (!ceph_mdsmap_is_cluster_available(fsc->mdsc->mdsmap)) { + /* ceph_mdsc_handle_mdsmap() replaces and frees the mdsmap */ + mutex_lock(&fsc->mdsc->mutex); + available = ceph_mdsmap_is_cluster_available(fsc->mdsc->mdsmap); + mutex_unlock(&fsc->mdsc->mutex); + if (!available) { pr_info("No mds server is up or the cluster is laggy\n"); err = -EHOSTUNREACH; } -- 2.53.0