[PATCH] sanitize handling of shared descriptor tables in failing execve()

* unshare_files() can fail; doing it after irreversible actions is wrong
  and de_thread() is certainly irreversible.
* since we do it unconditionally anyway, we might as well do it in do_execve()
  and save ourselves the PITA in binfmt handlers, etc.
* while we are at it, binfmt_som actually leaked files_struct on failure.

As a side benefit, unshare_files(), put_files_struct() and reset_files_struct()
become unexported.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/binfmt_elf.c

@@ -543,7 +543,6 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 	unsigned long interp_load_addr = 0;
 	unsigned long start_code, end_code, start_data, end_data;
 	unsigned long reloc_func_desc = 0;
-	struct files_struct *files;
 	int executable_stack = EXSTACK_DEFAULT;
 	unsigned long def_flags = 0;
 	struct {
@@ -593,20 +592,9 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 		goto out_free_ph;
 	}
 
-	files = current->files;	/* Refcounted so ok */
-	retval = unshare_files();
-	if (retval < 0)
-		goto out_free_ph;
-	if (files == current->files) {
-		put_files_struct(files);
-		files = NULL;
-	}
-
-	/* exec will make our files private anyway, but for the a.out
-	   loader stuff we need to do it earlier */
 	retval = get_unused_fd();
 	if (retval < 0)
-		goto out_free_fh;
+		goto out_free_ph;
 	get_file(bprm->file);
 	fd_install(elf_exec_fileno = retval, bprm->file);
 
@@ -728,12 +716,6 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 	if (retval)
 		goto out_free_dentry;
 
-	/* Discard our unneeded old files struct */
-	if (files) {
-		put_files_struct(files);
-		files = NULL;
-	}
-
 	/* OK, This is the point of no return */
 	current->flags &= ~PF_FORKNOEXEC;
 	current->mm->def_flags = def_flags;
@@ -1016,9 +998,6 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 	kfree(elf_interpreter);
 out_free_file:
 	sys_close(elf_exec_fileno);
-out_free_fh:
-	if (files)
-		reset_files_struct(current, files);
 out_free_ph:
 	kfree(elf_phdata);
 	goto out;

fs/binfmt_misc.c

@@ -110,7 +110,6 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 	char *iname_addr = iname;
 	int retval;
 	int fd_binary = -1;
-	struct files_struct *files = NULL;
 
 	retval = -ENOEXEC;
 	if (!enabled)
@@ -133,21 +132,13 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 
 	if (fmt->flags & MISC_FMT_OPEN_BINARY) {
 
-		files = current->files;
-		retval = unshare_files();
-		if (retval < 0)
-			goto _ret;
-		if (files == current->files) {
-			put_files_struct(files);
-			files = NULL;
-		}
 		/* if the binary should be opened on behalf of the
 		 * interpreter than keep it open and assign descriptor
 		 * to it */
  		fd_binary = get_unused_fd();
  		if (fd_binary < 0) {
  			retval = fd_binary;
- 			goto _unshare;
+ 			goto _ret;
  		}
  		fd_install(fd_binary, bprm->file);
 
@@ -205,10 +196,6 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 	if (retval < 0)
 		goto _error;
 
-	if (files) {
-		put_files_struct(files);
-		files = NULL;
-	}
 _ret:
 	return retval;
 _error:
@@ -216,9 +203,6 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 		sys_close(fd_binary);
 	bprm->interp_flags = 0;
 	bprm->interp_data = 0;
-_unshare:
-	if (files)
-		reset_files_struct(current, files);
 	goto _ret;
 }
 

fs/binfmt_som.c

@@ -194,7 +194,6 @@ load_som_binary(struct linux_binprm * bprm, struct pt_regs * regs)
 	unsigned long som_entry;
 	struct som_hdr *som_ex;
 	struct som_exec_auxhdr *hpuxhdr;
-	struct files_struct *files;
 
 	/* Get the exec-header */
 	som_ex = (struct som_hdr *) bprm->buf;
@@ -221,15 +220,6 @@ load_som_binary(struct linux_binprm * bprm, struct pt_regs * regs)
 		goto out_free;
 	}
 
-	files = current->files; /* Refcounted so ok */
-	retval = unshare_files();
-	if (retval < 0)
-		goto out_free;
-	if (files == current->files) {
-		put_files_struct(files);
-		files = NULL;
-	}
-
 	retval = get_unused_fd();
 	if (retval < 0)
 		goto out_free;

fs/exec.c

@@ -953,7 +953,6 @@ int flush_old_exec(struct linux_binprm * bprm)
 {
 	char * name;
 	int i, ch, retval;
-	struct files_struct *files;
 	char tcomm[sizeof(current->comm)];
 
 	/*
@@ -964,27 +963,16 @@ int flush_old_exec(struct linux_binprm * bprm)
 	if (retval)
 		goto out;
 
-	/*
-	 * Make sure we have private file handles. Ask the
-	 * fork helper to do the work for us and the exit
-	 * helper to do the cleanup of the old one.
-	 */
-	files = current->files;		/* refcounted so safe to hold */
-	retval = unshare_files();
-	if (retval)
-		goto out;
 	/*
 	 * Release all of the old mmap stuff
 	 */
 	retval = exec_mmap(bprm->mm);
 	if (retval)
-		goto mmap_failed;
+		goto out;
 
 	bprm->mm = NULL;		/* We're using it now */
 
 	/* This is the point of no return */
-	put_files_struct(files);
-
 	current->sas_ss_sp = current->sas_ss_size = 0;
 
 	if (current->euid == current->uid && current->egid == current->gid)
@@ -1034,8 +1022,6 @@ int flush_old_exec(struct linux_binprm * bprm)
 
 	return 0;
 
-mmap_failed:
-	reset_files_struct(current, files);
 out:
 	return retval;
 }
@@ -1283,12 +1269,23 @@ int do_execve(char * filename,
 	struct linux_binprm *bprm;
 	struct file *file;
 	unsigned long env_p;
+	struct files_struct *files;
 	int retval;
 
+	files = current->files;
+	retval = unshare_files();
+	if (retval)
+		goto out_ret;
+
+	if (files == current->files) {
+		put_files_struct(files);
+		files = NULL;
+	}
+
 	retval = -ENOMEM;
 	bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
 	if (!bprm)
-		goto out_ret;
+		goto out_files;
 
 	file = open_exec(filename);
 	retval = PTR_ERR(file);
@@ -1343,6 +1340,8 @@ int do_execve(char * filename,
 		security_bprm_free(bprm);
 		acct_update_integrals(current);
 		kfree(bprm);
+		if (files)
+			put_files_struct(files);
 		return retval;
 	}
 
@@ -1363,6 +1362,9 @@ int do_execve(char * filename,
 out_kfree:
 	kfree(bprm);
 
+out_files:
+	if (files)
+		reset_files_struct(current, files);
 out_ret:
 	return retval;
 }

kernel/exit.c

@@ -507,8 +507,6 @@ void 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;
@@ -519,7 +517,6 @@ void reset_files_struct(struct task_struct *tsk, struct files_struct *files)
 	task_unlock(tsk);
 	put_files_struct(old);
 }
-EXPORT_SYMBOL(reset_files_struct);
 
 void exit_files(struct task_struct *tsk)
 {

kernel/fork.c

@@ -870,8 +870,6 @@ int unshare_files(void)
 	return error;
 }
 
-EXPORT_SYMBOL(unshare_files);
-
 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
 {
 	struct sighand_struct *sig;