[PATCH] unshare system call -v5: unshare files

If the file descriptor structure is being shared, allocate a new one and copy
information from the current, shared, structure.

Signed-off-by: Janak Desai <janak@us.ibm.com>
Cc: Al Viro <viro@ftp.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Cc: Andi Kleen <ak@muc.de>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 51 insertions, 30 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index d1aceaea3f33..8e88b374cee9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -620,32 +620,17 @@ out:
         return newf;
 }
 
-static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
+/*
+ * Allocate a new files structure and copy contents from the
+ * passed in files structure.
+ */
+static struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
 {
-        struct files_struct *oldf, *newf;
+        struct files_struct *newf;
         struct file **old_fds, **new_fds;
-        int open_files, size, i, error = 0, expand;
+        int open_files, size, i, expand;
         struct fdtable *old_fdt, *new_fdt;
 
-        /*
-         * A background process may not have any files ...
-         */
-        oldf = current->files;
-        if (!oldf)
-                goto out;
-
-        if (clone_flags & CLONE_FILES) {
-                atomic_inc(&oldf->count);
-                goto out;
-        }
-
-        /*
-         * Note: we may be using current for both targets (See exec.c)
-         * This works because we cache current->files (old) as oldf. Don't
-         * break this.
-         */
-        tsk->files = NULL;
-        error = -ENOMEM;
         newf = alloc_files();
         if (!newf)
                 goto out;
@@ -674,9 +659,9 @@ static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
         if (expand) {
                 spin_unlock(&oldf->file_lock);
                 spin_lock(&newf->file_lock);
-                error = expand_files(newf, open_files-1);
+                *errorp = expand_files(newf, open_files-1);
                 spin_unlock(&newf->file_lock);
-                if (error < 0)
+                if (*errorp < 0)
                         goto out_release;
                 new_fdt = files_fdtable(newf);
                 /*
@@ -725,10 +710,8 @@ static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
                 memset(&new_fdt->close_on_exec->fds_bits[start], 0, left);
         }
 
-        tsk->files = newf;
-        error = 0;
 out:
-        return error;
+        return newf;
 
 out_release:
         free_fdset (new_fdt->close_on_exec, new_fdt->max_fdset);
@@ -738,6 +721,40 @@ out_release:
         goto out;
 }
 
+static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
+{
+        struct files_struct *oldf, *newf;
+        int error = 0;
+
+        /*
+         * A background process may not have any files ...
+         */
+        oldf = current->files;
+        if (!oldf)
+                goto out;
+
+        if (clone_flags & CLONE_FILES) {
+                atomic_inc(&oldf->count);
+                goto out;
+        }
+
+        /*
+         * Note: we may be using current for both targets (See exec.c)
+         * This works because we cache current->files (old) as oldf. Don't
+         * break this.
+         */
+        tsk->files = NULL;
+        error = -ENOMEM;
+        newf = dup_fd(oldf, &error);
+        if (!newf)
+                goto out;
+
+        tsk->files = newf;
+        error = 0;
+out:
+        return error;
+}
+
 /*
  *      Helper to unshare the files of the current task.
  *      We don't want to expose copy_files internals to
@@ -1463,15 +1480,19 @@ static int unshare_vm(unsigned long unshare_flags, struct mm_struct **new_mmp)
 }
 
 /*
- * Unsharing of files for tasks created with CLONE_FILES is not supported yet
+ * Unshare file descriptor table if it is being shared
  */
 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
 {
         struct files_struct *fd = current->files;
+        int error = 0;
 
         if ((unshare_flags & CLONE_FILES) &&
-            (fd && atomic_read(&fd->count) > 1))
-                return -EINVAL;
+            (fd && atomic_read(&fd->count) > 1)) {
+                *new_fdp = dup_fd(fd, &error);
+                if (!*new_fdp)
+                        return error;
+        }
 
         return 0;
 }