Unrot uml mconsole a bit

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 18 insertions, 31 deletions

diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
index 51069245b79..3b3c36601a7 100644
--- a/arch/um/drivers/mconsole_kern.c
+++ b/arch/um/drivers/mconsole_kern.c
@@ -125,50 +125,36 @@ void mconsole_log(struct mc_request *req)
 void mconsole_proc(struct mc_request *req)
 {
         struct nameidata nd;
-        struct file_system_type *proc;
-        struct super_block *super;
+        struct vfsmount *mnt = current->nsproxy->pid_ns->proc_mnt;
         struct file *file;
         int n, err;
         char *ptr = req->request.data, *buf;
+        mm_segment_t old_fs = get_fs();
 
         ptr += strlen("proc");
         ptr = skip_spaces(ptr);
 
-        proc = get_fs_type("proc");
-        if (proc == NULL) {
-                mconsole_reply(req, "procfs not registered", 1, 0);
+        err = vfs_path_lookup(mnt->mnt_root, mnt, ptr, LOOKUP_FOLLOW, &nd);
+        if (err) {
+                mconsole_reply(req, "Failed to look up file", 1, 0);
                 goto out;
         }
 
-        super = (*proc->get_sb)(proc, 0, NULL, NULL);
-        put_filesystem(proc);
-        if (super == NULL) {
-                mconsole_reply(req, "Failed to get procfs superblock", 1, 0);
+        err = may_open(&nd.path, MAY_READ, FMODE_READ);
+        if (result) {
+                mconsole_reply(req, "Failed to open file", 1, 0);
+                path_put(&nd.path);
                 goto out;
         }
-        up_write(&super->s_umount);
-
-        nd.path.dentry = super->s_root;
-        nd.path.mnt = NULL;
-        nd.flags = O_RDONLY + 1;
-        nd.last_type = LAST_ROOT;
-
-        /* START: it was experienced that the stability problems are closed
-         * if commenting out these two calls + the below read cycle. To
-         * make UML crash again, it was enough to readd either one.*/
-        err = link_path_walk(ptr, &nd);
-        if (err) {
-                mconsole_reply(req, "Failed to look up file", 1, 0);
-                goto out_kill;
-        }
 
         file = dentry_open(nd.path.dentry, nd.path.mnt, O_RDONLY,
                            current_cred());
+        err = PTR_ERR(file);
         if (IS_ERR(file)) {
                 mconsole_reply(req, "Failed to open file", 1, 0);
-                goto out_kill;
+                path_put(&nd.path);
+                goto out;
         }
-        /*END*/
 
         buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
         if (buf == NULL) {
@@ -176,10 +162,13 @@ void mconsole_proc(struct mc_request *req)
                 goto out_fput;
         }
 
-        if ((file->f_op != NULL) && (file->f_op->read != NULL)) {
+        if (file->f_op->read) {
                 do {
-                        n = (*file->f_op->read)(file, buf, PAGE_SIZE - 1,
-                                                &file->f_pos);
+                        loff_t pos;
+                        set_fs(KERNEL_DS);
+                        n = vfs_read(file, buf, PAGE_SIZE - 1, &pos);
+                        file_pos_write(file, pos);
+                        set_fs(old_fs);
                         if (n >= 0) {
                                 buf[n] = '\0';
                                 mconsole_reply(req, buf, 0, (n > 0));
@@ -197,8 +186,6 @@ void mconsole_proc(struct mc_request *req)
         kfree(buf);
  out_fput:
         fput(file);
- out_kill:
-        deactivate_super(super);
  out: ;
 }
 #endif