Fix remount races with symlink handling in affs

A couple of fields in affs_sb_info is used in follow_link() and
symlink() for handling AFFS "absolute" symlinks.  Need locking
against affs_remount() updates.

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

1 files changed, 14 insertions, 3 deletions

diff --git a/fs/affs/super.c b/fs/affs/super.c
index b2a5958c6191..be6a6e8ed7d6 100644
--- a/fs/affs/super.c
+++ b/fs/affs/super.c
@@ -221,8 +221,6 @@ parse_options(char *options, uid_t *uid, gid_t *gid, int *mode, int *reserved, s
                         *mount_opts |= SF_MUFS;
                         break;
                 case Opt_prefix:
-                        /* Free any previous prefix */
-                        kfree(*prefix);
                         *prefix = match_strdup(&args[0]);
                         if (!*prefix)
                                 return 0;
@@ -311,6 +309,7 @@ static int affs_fill_super(struct super_block *sb, void *data, int silent)
                 return -ENOMEM;
         sb->s_fs_info = sbi;
         mutex_init(&sbi->s_bmlock);
+        spin_lock_init(&sbi->symlink_lock);
 
         if (!parse_options(data,&uid,&gid,&i,&reserved,&root_block,
                                 &blocksize,&sbi->s_prefix,
@@ -518,14 +517,18 @@ affs_remount(struct super_block *sb, int *flags, char *data)
         unsigned long            mount_flags;
         int                      res = 0;
         char                    *new_opts = kstrdup(data, GFP_KERNEL);
+        char                     volume[32];
+        char                    *prefix = NULL;
 
         pr_debug("AFFS: remount(flags=0x%x,opts=\"%s\")\n",*flags,data);
 
         *flags |= MS_NODIRATIME;
 
+        memcpy(volume, sbi->s_volume, 32);
         if (!parse_options(data, &uid, &gid, &mode, &reserved, &root_block,
-                           &blocksize, &sbi->s_prefix, sbi->s_volume,
+                           &blocksize, &prefix, volume,
                            &mount_flags)) {
+                kfree(prefix);
                 kfree(new_opts);
                 return -EINVAL;
         }
@@ -536,6 +539,14 @@ affs_remount(struct super_block *sb, int *flags, char *data)
         sbi->s_mode  = mode;
         sbi->s_uid   = uid;
         sbi->s_gid   = gid;
+        /* protect against readers */
+        spin_lock(&sbi->symlink_lock);
+        if (prefix) {
+                kfree(sbi->s_prefix);
+                sbi->s_prefix = prefix;
+        }
+        memcpy(sbi->s_volume, volume, 32);
+        spin_unlock(&sbi->symlink_lock);
 
         if ((*flags & MS_RDONLY) == (sb->s_flags & MS_RDONLY)) {
                 unlock_kernel();