[PATCH] Fix unserialized task->files changing

Fixed race on put_files_struct on exec with proc. Restoring files on current on error path may lead to proc having a pointer to already kfree-d files_struct. ->files changing at exit.c and khtread.c are safe as exit_files() makes all things under lock. Found during OpenVZ stress testing. [akpm@osdl.org: add export] Signed-off-by: Pavel Emelianov <xemul@openvz.org> Signed-off-by: Kirill Korotaev <dev@openvz.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
roblim · Sep 29, 2006 · 3b9b8ab · 3b9b8ab
1 parent fc09561
commit 3b9b8ab
Show file tree

Hide file tree

Showing 5 changed files with 18 additions and 10 deletions.
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
@@ -1038,10 +1038,8 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 out_free_file:
 	sys_close(elf_exec_fileno);
 out_free_fh:
-	if (files) {
-		put_files_struct(current->files);
-		current->files = files;
-	}
+	if (files)
+		reset_files_struct(current, files);
 out_free_ph:
 	kfree(elf_phdata);
 	goto out;

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
@@ -215,10 +215,8 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 	bprm->interp_flags = 0;
 	bprm->interp_data = 0;
 _unshare:
-	if (files) {
-		put_files_struct(current->files);
-		current->files = files;
-	}
+	if (files)
+		reset_files_struct(current, files);
 	goto _ret;
 }
 

diff --git a/fs/exec.c b/fs/exec.c
@@ -898,8 +898,7 @@ int flush_old_exec(struct linux_binprm * bprm)
 	return 0;
 
 mmap_failed:
-	put_files_struct(current->files);
-	current->files = files;
+	reset_files_struct(current, files);
 out:
 	return retval;
 }

diff --git a/include/linux/file.h b/include/linux/file.h
@@ -112,5 +112,6 @@ struct task_struct;
 
 struct files_struct *get_files_struct(struct task_struct *);
 void FASTCALL(put_files_struct(struct files_struct *fs));
+void reset_files_struct(struct task_struct *, struct files_struct *);
 
 #endif /* __LINUX_FILE_H */
diff --git a/kernel/exit.c b/kernel/exit.c
@@ -487,6 +487,18 @@ void fastcall put_files_struct(struct files_struct *files)
 
 EXPORT_SYMBOL(put_files_struct);
 
+void reset_files_struct(struct task_struct *tsk, struct files_struct *files)
+{
+	struct files_struct *old;
+
+	old = tsk->files;
+	task_lock(tsk);
+	tsk->files = files;
+	task_unlock(tsk);
+	put_files_struct(old);
+}
+EXPORT_SYMBOL(reset_files_struct);
+
 static inline void __exit_files(struct task_struct *tsk)
 {
 	struct files_struct * files = tsk->files;