From 6e6aad5facac2724df4bc6d8bb05151b05dcfa3f Mon Sep 17 00:00:00 2001 From: Li Lingfeng Date: Mon, 16 Jun 2025 12:01:27 +0800 Subject: [PATCH 1/2] nfs: clear SB_RDONLY before getting superblock mainline inclusion from mainline-v6.16-rc1 commit 8cd9b785943c57a136536250da80ba1eb6f8eb18 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/IBNEQX CVE: NA Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8cd9b785943c57a136536250da80ba1eb6f8eb18 -------------------------------- As described in the link, commit 52cb7f8f1778 ("nfs: ignore SB_RDONLY when mounting nfs") removed the check for the ro flag when determining whether to share the superblock, which caused issues when mounting different subdirectories under the same export directory via NFSv3. However, this change did not affect NFSv4. For NFSv3: 1) A single superblock is created for the initial mount. 2) When mounted read-only, this superblock carries the SB_RDONLY flag. 3) Before commit 52cb7f8f1778 ("nfs: ignore SB_RDONLY when mounting nfs"): Subsequent rw mounts would not share the existing ro superblock due to flag mismatch, creating a new superblock without SB_RDONLY. After the commit: The SB_RDONLY flag is ignored during superblock comparison, and this leads to sharing the existing superblock even for rw mounts. Ultimately results in write operations being rejected at the VFS layer. For NFSv4: 1) Multiple superblocks are created and the last one will be kept. 2) The actually used superblock for ro mounts doesn't carry SB_RDONLY flag. Therefore, commit 52cb7f8f1778 doesn't affect NFSv4 mounts. Clear SB_RDONLY before getting superblock when NFS_MOUNT_UNSHARED is not set to fix it. Fixes: 52cb7f8f1778 ("nfs: ignore SB_RDONLY when mounting nfs") Closes: https://lore.kernel.org/all/12d7ea53-1202-4e21-a7ef-431c94758ce5@app.fastmail.com/T/ Signed-off-by: Li Lingfeng Signed-off-by: Anna Schumaker Signed-off-by: Li Lingfeng --- fs/nfs/super.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/fs/nfs/super.c b/fs/nfs/super.c index b905a3d48100..f61448894c54 100644 --- a/fs/nfs/super.c +++ b/fs/nfs/super.c @@ -1289,8 +1289,17 @@ int nfs_get_tree_common(struct fs_context *fc) if (IS_ERR(server)) return PTR_ERR(server); + /* + * When NFS_MOUNT_UNSHARED is not set, NFS forces the sharing of a + * superblock among each filesystem that mounts sub-directories + * belonging to a single exported root path. + * To prevent interference between different filesystems, the + * SB_RDONLY flag should be removed from the superblock. + */ if (server->flags & NFS_MOUNT_UNSHARED) compare_super = NULL; + else + fc->sb_flags &= ~SB_RDONLY; /* -o noac implies -o sync */ if (server->flags & NFS_MOUNT_NOAC) -- Gitee From f75d4f3cdff0a1ed2f73e0ac06f30023bfb999cf Mon Sep 17 00:00:00 2001 From: Li Lingfeng Date: Mon, 16 Jun 2025 12:01:28 +0800 Subject: [PATCH 2/2] nfs: ignore SB_RDONLY when remounting nfs mainline inclusion from mainline-v6.16-rc1 commit 80c4de6ab44c14e910117a02f2f8241ffc6ec54a category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/IBNEQX CVE: NA Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=80c4de6ab44c14e910117a02f2f8241ffc6ec54a -------------------------------- In some scenarios, when mounting NFS, more than one superblock may be created. The final superblock used is the last one created, but only the first superblock carries the ro flag passed from user space. If a ro flag is added to the superblock via remount, it will trigger the issue described in Link[1]. Link[2] attempted to address this by marking the superblock as ro during the initial mount. However, this introduced a new problem in scenarios where multiple mount points share the same superblock: [root@a ~]# mount /dev/sdb /mnt/sdb [root@a ~]# echo "/mnt/sdb *(rw,no_root_squash)" > /etc/exports [root@a ~]# echo "/mnt/sdb/test_dir2 *(ro,no_root_squash)" >> /etc/exports [root@a ~]# systemctl restart nfs-server [root@a ~]# mount -t nfs -o rw 127.0.0.1:/mnt/sdb/test_dir1 /mnt/test_mp1 [root@a ~]# mount | grep nfs4 127.0.0.1:/mnt/sdb/test_dir1 on /mnt/test_mp1 type nfs4 (rw,relatime,... [root@a ~]# mount -t nfs -o ro 127.0.0.1:/mnt/sdb/test_dir2 /mnt/test_mp2 [root@a ~]# mount | grep nfs4 127.0.0.1:/mnt/sdb/test_dir1 on /mnt/test_mp1 type nfs4 (ro,relatime,... 127.0.0.1:/mnt/sdb/test_dir2 on /mnt/test_mp2 type nfs4 (ro,relatime,... [root@a ~]# When mounting the second NFS, the shared superblock is marked as ro, causing the previous NFS mount to become read-only. To resolve both issues, the ro flag is no longer applied to the superblock during remount. Instead, the ro flag on the mount is used to control whether the mount point is read-only. Fixes: 281cad46b34d ("NFS: Create a submount rpc_op") Link[1]: https://lore.kernel.org/all/20240604112636.236517-3-lilingfeng@huaweicloud.com/ Link[2]: https://lore.kernel.org/all/20241130035818.1459775-1-lilingfeng3@huawei.com/ Signed-off-by: Li Lingfeng Signed-off-by: Anna Schumaker Signed-off-by: Li Lingfeng --- fs/nfs/super.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/fs/nfs/super.c b/fs/nfs/super.c index f61448894c54..05d30a97c1ee 100644 --- a/fs/nfs/super.c +++ b/fs/nfs/super.c @@ -1022,6 +1022,16 @@ int nfs_reconfigure(struct fs_context *fc) sync_filesystem(sb); + /* + * The SB_RDONLY flag has been removed from the superblock during + * mounts to prevent interference between different filesystems. + * Similarly, it is also necessary to ignore the SB_RDONLY flag + * during reconfiguration; otherwise, it may also result in the + * creation of redundant superblocks when mounting a directory with + * different rw and ro flags multiple times. + */ + fc->sb_flags_mask &= ~SB_RDONLY; + /* * Userspace mount programs that send binary options generally send * them populated with default values. We have no way to know which -- Gitee