[06/86] proc: change ->nlink under proc_subdir_lock

Commit Message

Andrew Morton Dec. 5, 2019, 12:49 a.m. UTC

From: Alexey Dobriyan <[e-mail]>
Subject: proc: change ->nlink under proc_subdir_lock

Currently gluing PDE into global /proc tree is done under lock, but
changing ->nlink is not.  Additionally struct proc_dir_entry::nlink is not
atomic so updates can be lost.

Link: http://lkml.kernel.org/r/20190925202436.GA17388@avx2
Signed-off-by: Alexey Dobriyan <[e-mail]>
Cc: Al Viro <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 fs/proc/generic.c |   31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)

Patch

--- a/fs/proc/generic.c~proc-change-nlink-under-proc_subdir_lock
+++ a/fs/proc/generic.c
@@ -138,8 +138,12 @@  static int proc_getattr(const struct pat
 {
 	struct inode *inode = d_inode(path->dentry);
 	struct proc_dir_entry *de = PDE(inode);
-	if (de && de->nlink)
-		set_nlink(inode, de->nlink);
+	if (de) {
+		nlink_t nlink = READ_ONCE(de->nlink);
+		if (nlink > 0) {
+			set_nlink(inode, nlink);
+		}
+	}
 
 	generic_fillattr(inode, stat);
 	return 0;
@@ -362,6 +366,7 @@  struct proc_dir_entry *proc_register(str
 		write_unlock(&proc_subdir_lock);
 		goto out_free_inum;
 	}
+	dir->nlink++;
 	write_unlock(&proc_subdir_lock);
 
 	return dp;
@@ -472,10 +477,7 @@  struct proc_dir_entry *proc_mkdir_data(c
 		ent->data = data;
 		ent->proc_fops = &proc_dir_operations;
 		ent->proc_iops = &proc_dir_inode_operations;
-		parent->nlink++;
 		ent = proc_register(parent, ent);
-		if (!ent)
-			parent->nlink--;
 	}
 	return ent;
 }
@@ -505,10 +507,7 @@  struct proc_dir_entry *proc_create_mount
 		ent->data = NULL;
 		ent->proc_fops = NULL;
 		ent->proc_iops = NULL;
-		parent->nlink++;
 		ent = proc_register(parent, ent);
-		if (!ent)
-			parent->nlink--;
 	}
 	return ent;
 }
@@ -666,8 +665,12 @@  void remove_proc_entry(const char *name,
 	len = strlen(fn);
 
 	de = pde_subdir_find(parent, fn, len);
-	if (de)
+	if (de) {
 		rb_erase(&de->subdir_node, &parent->subdir);
+		if (S_ISDIR(de->mode)) {
+			parent->nlink--;
+		}
+	}
 	write_unlock(&proc_subdir_lock);
 	if (!de) {
 		WARN(1, "name '%s'\n", name);
@@ -676,9 +679,6 @@  void remove_proc_entry(const char *name,
 
 	proc_entry_rundown(de);
 
-	if (S_ISDIR(de->mode))
-		parent->nlink--;
-	de->nlink = 0;
 	WARN(pde_subdir_first(de),
 	     "%s: removing non-empty directory '%s/%s', leaking at least '%s'\n",
 	     __func__, de->parent->name, de->name, pde_subdir_first(de)->name);
@@ -714,13 +714,12 @@  int remove_proc_subtree(const char *name
 			de = next;
 			continue;
 		}
-		write_unlock(&proc_subdir_lock);
-
-		proc_entry_rundown(de);
 		next = de->parent;
 		if (S_ISDIR(de->mode))
 			next->nlink--;
-		de->nlink = 0;
+		write_unlock(&proc_subdir_lock);
+
+		proc_entry_rundown(de);
 		if (de == root)
 			break;
 		pde_put(de);