ANDROID: sdcardfs: override umask on mkdir and create

The mode on files created on the lower fs should
not be affected by the umask of the calling
task's fs_struct. Instead, we create a copy
and modify it as needed. This also lets us avoid
the string shenanigans around .nomedia files.

Bug: 27992761
Change-Id: Ia3a6e56c24c6e19b3b01c1827e46403bb71c2f4c
Signed-off-by: Daniel Rosenberg <drosen@google.com>

diff --git a/fs/fs_struct.c b/fs/fs_struct.c
index 7dca743b2ce1c8796155a14c3d3a83023eed3de4..005dcb4013695d5b7d681c0cc1f3113ba79ef54c 100644 (file)
--- a/fs/fs_struct.c
+++ b/fs/fs_struct.c
@@ -127,6 +127,7 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old)
        }
        return fs;
 }
+EXPORT_SYMBOL_GPL(copy_fs_struct);
 
 int unshare_fs_struct(void)
 {

diff --git a/fs/sdcardfs/inode.c b/fs/sdcardfs/inode.c
index 2528da0d3ae181dbdc030b804da5ce8f45932cbb..4b140ba8695597c34a4dbf5498601d4b8251e8a7 100644 (file)
--- a/fs/sdcardfs/inode.c
+++ b/fs/sdcardfs/inode.c
@@ -19,6 +19,7 @@
  */
 
 #include "sdcardfs.h"
+#include <linux/fs_struct.h>
 
 /* Do not directly use this function. Use OVERRIDE_CRED() instead. */
 const struct cred * override_fsids(struct sdcardfs_sb_info* sbi)
@@ -56,6 +57,8 @@ static int sdcardfs_create(struct inode *dir, struct dentry *dentry,
        struct dentry *lower_parent_dentry = NULL;
        struct path lower_path;
        const struct cred *saved_cred = NULL;
+       struct fs_struct *saved_fs;
+       struct fs_struct *copied_fs;
 
        if(!check_caller_access_to_name(dir, dentry->d_name.name)) {
                printk(KERN_INFO "%s: need to check the caller's gid in packages.list\n"
@@ -74,6 +77,16 @@ static int sdcardfs_create(struct inode *dir, struct dentry *dentry,
 
        /* set last 16bytes of mode field to 0664 */
        mode = (mode & S_IFMT) | 00664;
+
+       /* temporarily change umask for lower fs write */
+       saved_fs = current->fs;
+       copied_fs = copy_fs_struct(current->fs);
+       if (!copied_fs) {
+               err = -ENOMEM;
+               goto out_unlock;
+       }
+       current->fs = copied_fs;
+       current->fs->umask = 0;
        err = vfs_create(d_inode(lower_parent_dentry), lower_dentry, mode, want_excl);
        if (err)
                goto out;
@@ -85,6 +98,9 @@ static int sdcardfs_create(struct inode *dir, struct dentry *dentry,
        fsstack_copy_inode_size(dir, d_inode(lower_parent_dentry));
 
 out:
+       current->fs = saved_fs;
+       free_fs_struct(copied_fs);
+out_unlock:
        unlock_dir(lower_parent_dentry);
        sdcardfs_put_lower_path(dentry, &lower_path);
        REVERT_CRED(saved_cred);
@@ -245,11 +261,9 @@ static int sdcardfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode
        struct sdcardfs_sb_info *sbi = SDCARDFS_SB(dentry->d_sb);
        const struct cred *saved_cred = NULL;
        struct sdcardfs_inode_info *pi = SDCARDFS_I(dir);
-       char *page_buf;
-       char *nomedia_dir_name;
-       char *nomedia_fullpath;
-       int fullpath_namelen;
        int touch_err = 0;
+       struct fs_struct *saved_fs;
+       struct fs_struct *copied_fs;
 
        if(!check_caller_access_to_name(dir, dentry->d_name.name)) {
                printk(KERN_INFO "%s: need to check the caller's gid in packages.list\n"
@@ -276,6 +290,16 @@ static int sdcardfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode
 
        /* set last 16bytes of mode field to 0775 */
        mode = (mode & S_IFMT) | 00775;
+
+       /* temporarily change umask for lower fs write */
+       saved_fs = current->fs;
+       copied_fs = copy_fs_struct(current->fs);
+       if (!copied_fs) {
+               err = -ENOMEM;
+               goto out_unlock;
+       }
+       current->fs = copied_fs;
+       current->fs->umask = 0;
        err = vfs_mkdir(d_inode(lower_parent_dentry), lower_dentry, mode);
 
        if (err)
@@ -316,42 +340,18 @@ static int sdcardfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode
        /* When creating /Android/data and /Android/obb, mark them as .nomedia */
        if (make_nomedia_in_obb ||
                ((pi->perm == PERM_ANDROID) && (!strcasecmp(dentry->d_name.name, "data")))) {
-
-               page_buf = (char *)__get_free_page(GFP_KERNEL);
-               if (!page_buf) {
-                       printk(KERN_ERR "sdcardfs: failed to allocate page buf\n");
-                       goto out;
-               }
-
-               nomedia_dir_name = d_absolute_path(&lower_path, page_buf, PAGE_SIZE);
-               if (IS_ERR(nomedia_dir_name)) {
-                       free_page((unsigned long)page_buf);
-                       printk(KERN_ERR "sdcardfs: failed to get .nomedia dir name\n");
-                       goto out;
-               }
-
-               fullpath_namelen = page_buf + PAGE_SIZE - nomedia_dir_name - 1;
-               fullpath_namelen += strlen("/.nomedia");
-               nomedia_fullpath = kzalloc(fullpath_namelen + 1, GFP_KERNEL);
-               if (!nomedia_fullpath) {
-                       free_page((unsigned long)page_buf);
-                       printk(KERN_ERR "sdcardfs: failed to allocate .nomedia fullpath buf\n");
-                       goto out;
-               }
-
-               strcpy(nomedia_fullpath, nomedia_dir_name);
-               free_page((unsigned long)page_buf);
-               strcat(nomedia_fullpath, "/.nomedia");
-               touch_err = touch(nomedia_fullpath, 0664);
+               set_fs_pwd(current->fs, &lower_path);
+               touch_err = touch(".nomedia", 0664);
                if (touch_err) {
-                       printk(KERN_ERR "sdcardfs: failed to touch(%s): %d\n",
-                                                       nomedia_fullpath, touch_err);
-                       kfree(nomedia_fullpath);
+                       printk(KERN_ERR "sdcardfs: failed to create .nomedia in %s: %d\n",
+                                                       lower_path.dentry->d_name.name, touch_err);
                        goto out;
                }
-               kfree(nomedia_fullpath);
        }
 out:
+       current->fs = saved_fs;
+       free_fs_struct(copied_fs);
+out_unlock:
        unlock_dir(lower_parent_dentry);
        sdcardfs_put_lower_path(dentry, &lower_path);
 out_revert: