[PATCH] protect remove_proc_entry

It has been discovered that the remove_proc_entry has a race in the removing
of entries in the proc file system that are siblings.  There's no protection
around the traversing and removing of elements that belong in the same
subdirectory.

This subdirectory list is protected in other areas by the BKL.  So the BKL was
at first used to protect this area too, but unfortunately, remove_proc_entry
may be called with spinlocks held.  The BKL may schedule, so this was not a
solution.

The final solution was to add a new global spin lock to protect this list,
called proc_subdir_lock.  This lock now protects the list in
remove_proc_entry, and I also went around looking for other areas that this
list is modified and added this protection there too.  Care must be taken
since these locations call several functions that may also schedule.

Since I don't see any location that these functions that modify the
subdirectory list are called by interrupts, the irqsave/restore versions of
the spin lock was _not_ used.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 29 insertions, 3 deletions

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 20e5c4509a43..47b7a20d45eb 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -19,6 +19,7 @@
 #include <linux/idr.h>
 #include <linux/namei.h>
 #include <linux/bitops.h>
+#include <linux/spinlock.h>
 #include <asm/uaccess.h>
 
 #include "internal.h"
@@ -29,6 +30,8 @@ static ssize_t proc_file_write(struct file *file, const char __user *buffer,
                                size_t count, loff_t *ppos);
 static loff_t proc_file_lseek(struct file *, loff_t, int);
 
+DEFINE_SPINLOCK(proc_subdir_lock);
+
 int proc_match(int len, const char *name, struct proc_dir_entry *de)
 {
         if (de->namelen != len)
@@ -277,7 +280,9 @@ static int xlate_proc_name(const char *name,
         const char              *cp = name, *next;
         struct proc_dir_entry   *de;
         int                     len;
+        int                     rtn = 0;
 
+        spin_lock(&proc_subdir_lock);
         de = &proc_root;
         while (1) {
                 next = strchr(cp, '/');
@@ -289,13 +294,17 @@ static int xlate_proc_name(const char *name,
                         if (proc_match(len, cp, de))
                                 break;
                 }
-                if (!de)
-                        return -ENOENT;
+                if (!de) {
+                        rtn = -ENOENT;
+                        goto out;
+                }
                 cp += len + 1;
         }
         *residual = cp;
         *ret = de;
-        return 0;
+out:
+        spin_unlock(&proc_subdir_lock);
+        return rtn;
 }
 
 static DEFINE_IDR(proc_inum_idr);
@@ -380,6 +389,7 @@ struct dentry *proc_lookup(struct inode * dir, struct dentry *dentry, struct nam
         int error = -ENOENT;
 
         lock_kernel();
+        spin_lock(&proc_subdir_lock);
         de = PDE(dir);
         if (de) {
                 for (de = de->subdir; de ; de = de->next) {
@@ -388,12 +398,15 @@ struct dentry *proc_lookup(struct inode * dir, struct dentry *dentry, struct nam
                         if (!memcmp(dentry->d_name.name, de->name, de->namelen)) {
                                 unsigned int ino = de->low_ino;
 
+                                spin_unlock(&proc_subdir_lock);
                                 error = -EINVAL;
                                 inode = proc_get_inode(dir->i_sb, ino, de);
+                                spin_lock(&proc_subdir_lock);
                                 break;
                         }
                 }
         }
+        spin_unlock(&proc_subdir_lock);
         unlock_kernel();
 
         if (inode) {
@@ -447,11 +460,13 @@ int proc_readdir(struct file * filp,
                         filp->f_pos++;
                         /* fall through */
                 default:
+                        spin_lock(&proc_subdir_lock);
                         de = de->subdir;
                         i -= 2;
                         for (;;) {
                                 if (!de) {
                                         ret = 1;
+                                        spin_unlock(&proc_subdir_lock);
                                         goto out;
                                 }
                                 if (!i)
@@ -461,12 +476,16 @@ int proc_readdir(struct file * filp,
                         }
 
                         do {
+                                /* filldir passes info to user space */
+                                spin_unlock(&proc_subdir_lock);
                                 if (filldir(dirent, de->name, de->namelen, filp->f_pos,
                                             de->low_ino, de->mode >> 12) < 0)
                                         goto out;
+                                spin_lock(&proc_subdir_lock);
                                 filp->f_pos++;
                                 de = de->next;
                         } while (de);
+                        spin_unlock(&proc_subdir_lock);
         }
         ret = 1;
 out:    unlock_kernel();
@@ -500,9 +519,13 @@ static int proc_register(struct proc_dir_entry * dir, struct proc_dir_entry * dp
         if (i == 0)
                 return -EAGAIN;
         dp->low_ino = i;
+
+        spin_lock(&proc_subdir_lock);
         dp->next = dir->subdir;
         dp->parent = dir;
         dir->subdir = dp;
+        spin_unlock(&proc_subdir_lock);
+
         if (S_ISDIR(dp->mode)) {
                 if (dp->proc_iops == NULL) {
                         dp->proc_fops = &proc_dir_operations;
@@ -694,6 +717,8 @@ void remove_proc_entry(const char *name, struct proc_dir_entry *parent)
         if (!parent && xlate_proc_name(name, &parent, &fn) != 0)
                 goto out;
         len = strlen(fn);
+
+        spin_lock(&proc_subdir_lock);
         for (p = &parent->subdir; *p; p=&(*p)->next ) {
                 if (!proc_match(len, fn, *p))
                         continue;
@@ -714,6 +739,7 @@ void remove_proc_entry(const char *name, struct proc_dir_entry *parent)
                 }
                 break;
         }
+        spin_unlock(&proc_subdir_lock);
 out:
         return;
 }