5.15-stable review patch. If anyone has any objections, please let me know.
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From: Li Lingfeng lilingfeng3@huawei.com
[ Upstream commit 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.c... Link[2]: https://lore.kernel.org/all/20241130035818.1459775-1-lilingfeng3@huawei.com/ Signed-off-by: Li Lingfeng lilingfeng3@huawei.com Signed-off-by: Anna Schumaker anna.schumaker@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/nfs/super.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/fs/nfs/super.c b/fs/nfs/super.c index aa11a6dcf6ce7..cc70800b9a4b2 100644 --- a/fs/nfs/super.c +++ b/fs/nfs/super.c @@ -1017,6 +1017,16 @@ 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