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authorAmir Goldstein <amir73il@gmail.com>2023-06-15 14:22:28 +0300
committerChristian Brauner <brauner@kernel.org>2023-06-19 18:16:38 +0200
commit62d53c4a1dfe347bd87ede46ffad38c9a3870338 (patch)
tree50bf37201de8a425c8e4cc23b1be69bde2e4b6eb /fs
parent8a05a8c31d06c5d0d67b273a4a00f87269adde82 (diff)
fs: use backing_file container for internal files with "fake" f_path
Overlayfs uses open_with_fake_path() to allocate internal kernel files, with a "fake" path - whose f_path is not on the same fs as f_inode. Allocate a container struct backing_file for those internal files, that is used to hold the "fake" ovl path along with the real path. backing_file_real_path() can be used to access the stored real path. Signed-off-by: Amir Goldstein <amir73il@gmail.com> Message-Id: <20230615112229.2143178-5-amir73il@gmail.com> Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/file_table.c50
-rw-r--r--fs/internal.h5
-rw-r--r--fs/open.c45
-rw-r--r--fs/overlayfs/file.c4
4 files changed, 86 insertions, 18 deletions
diff --git a/fs/file_table.c b/fs/file_table.c
index 4bc713865212..e06c68e2d757 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -44,18 +44,40 @@ static struct kmem_cache *filp_cachep __read_mostly;
static struct percpu_counter nr_files __cacheline_aligned_in_smp;
+/* Container for backing file with optional real path */
+struct backing_file {
+ struct file file;
+ struct path real_path;
+};
+
+static inline struct backing_file *backing_file(struct file *f)
+{
+ return container_of(f, struct backing_file, file);
+}
+
+struct path *backing_file_real_path(struct file *f)
+{
+ return &backing_file(f)->real_path;
+}
+EXPORT_SYMBOL_GPL(backing_file_real_path);
+
static void file_free_rcu(struct rcu_head *head)
{
struct file *f = container_of(head, struct file, f_rcuhead);
put_cred(f->f_cred);
- kmem_cache_free(filp_cachep, f);
+ if (unlikely(f->f_mode & FMODE_BACKING))
+ kfree(backing_file(f));
+ else
+ kmem_cache_free(filp_cachep, f);
}
static inline void file_free(struct file *f)
{
security_file_free(f);
- if (!(f->f_mode & FMODE_NOACCOUNT))
+ if (unlikely(f->f_mode & FMODE_BACKING))
+ path_put(backing_file_real_path(f));
+ if (likely(!(f->f_mode & FMODE_NOACCOUNT)))
percpu_counter_dec(&nr_files);
call_rcu(&f->f_rcuhead, file_free_rcu);
}
@@ -226,6 +248,30 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred)
return f;
}
+/*
+ * Variant of alloc_empty_file() that allocates a backing_file container
+ * and doesn't check and modify nr_files.
+ *
+ * This is only for kernel internal use, and the allocate file must not be
+ * installed into file tables or such.
+ */
+struct file *alloc_empty_backing_file(int flags, const struct cred *cred)
+{
+ struct backing_file *ff;
+ int error;
+
+ ff = kzalloc(sizeof(struct backing_file), GFP_KERNEL);
+ if (unlikely(!ff))
+ return ERR_PTR(-ENOMEM);
+
+ error = init_file(&ff->file, flags, cred);
+ if (unlikely(error))
+ return ERR_PTR(error);
+
+ ff->file.f_mode |= FMODE_BACKING | FMODE_NOACCOUNT;
+ return &ff->file;
+}
+
/**
* alloc_file - allocate and initialize a 'struct file'
*
diff --git a/fs/internal.h b/fs/internal.h
index bd3b2810a36b..9c31078e0d16 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -97,8 +97,9 @@ extern void chroot_fs_refs(const struct path *, const struct path *);
/*
* file_table.c
*/
-extern struct file *alloc_empty_file(int, const struct cred *);
-extern struct file *alloc_empty_file_noaccount(int, const struct cred *);
+struct file *alloc_empty_file(int flags, const struct cred *cred);
+struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred);
+struct file *alloc_empty_backing_file(int flags, const struct cred *cred);
static inline void put_file_access(struct file *file)
{
diff --git a/fs/open.c b/fs/open.c
index 322e017bf480..81186b277815 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1149,23 +1149,44 @@ struct file *kernel_file_open(const struct path *path, int flags,
}
EXPORT_SYMBOL_GPL(kernel_file_open);
-struct file *open_with_fake_path(const struct path *path, int flags,
- struct inode *inode, const struct cred *cred)
+/**
+ * backing_file_open - open a backing file for kernel internal use
+ * @path: path of the file to open
+ * @flags: open flags
+ * @path: path of the backing file
+ * @cred: credentials for open
+ *
+ * Open a backing file for a stackable filesystem (e.g., overlayfs).
+ * @path may be on the stackable filesystem and backing inode on the
+ * underlying filesystem. In this case, we want to be able to return
+ * the @real_path of the backing inode. This is done by embedding the
+ * returned file into a container structure that also stores the path of
+ * the backing inode on the underlying filesystem, which can be
+ * retrieved using backing_file_real_path().
+ */
+struct file *backing_file_open(const struct path *path, int flags,
+ const struct path *real_path,
+ const struct cred *cred)
{
- struct file *f = alloc_empty_file_noaccount(flags, cred);
- if (!IS_ERR(f)) {
- int error;
+ struct file *f;
+ int error;
- f->f_path = *path;
- error = do_dentry_open(f, inode, NULL);
- if (error) {
- fput(f);
- f = ERR_PTR(error);
- }
+ f = alloc_empty_backing_file(flags, cred);
+ if (IS_ERR(f))
+ return f;
+
+ f->f_path = *path;
+ path_get(real_path);
+ *backing_file_real_path(f) = *real_path;
+ error = do_dentry_open(f, d_inode(real_path->dentry), NULL);
+ if (error) {
+ fput(f);
+ f = ERR_PTR(error);
}
+
return f;
}
-EXPORT_SYMBOL(open_with_fake_path);
+EXPORT_SYMBOL_GPL(backing_file_open);
#define WILL_CREATE(flags) (flags & (O_CREAT | __O_TMPFILE))
#define O_PATH_FLAGS (O_DIRECTORY | O_NOFOLLOW | O_PATH | O_CLOEXEC)
diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 7c04f033aadd..71fa6c83f093 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -61,8 +61,8 @@ static struct file *ovl_open_realfile(const struct file *file,
if (!inode_owner_or_capable(real_idmap, realinode))
flags &= ~O_NOATIME;
- realfile = open_with_fake_path(&file->f_path, flags, realinode,
- current_cred());
+ realfile = backing_file_open(&file->f_path, flags, realpath,
+ current_cred());
}
revert_creds(old_cred);