From 6b335d9c80d7f3c2a3f6545f664ae9007a0f3821 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Tue, 22 Apr 2008 04:45:46 -0400
Subject: [PATCH] close race in unshare_files()

updating current->files requires task_lock

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 kernel/fork.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

(limited to 'kernel')

diff --git a/kernel/fork.c b/kernel/fork.c
index 89fe414645e9..76f05a08062b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -805,12 +805,6 @@ static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
 		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;
 	newf = dup_fd(oldf, &error);
 	if (!newf)
 		goto out;
@@ -855,7 +849,8 @@ static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
 int unshare_files(void)
 {
 	struct files_struct *files  = current->files;
-	int rc;
+	struct files_struct *newf;
+	int error = 0;
 
 	BUG_ON(!files);
 
@@ -866,10 +861,13 @@ int unshare_files(void)
 		atomic_inc(&files->count);
 		return 0;
 	}
-	rc = copy_files(0, current);
-	if(rc)
-		current->files = files;
-	return rc;
+	newf = dup_fd(files, &error);
+	if (newf) {
+		task_lock(current);
+		current->files = newf;
+		task_unlock(current);
+	}
+	return error;
 }
 
 EXPORT_SYMBOL(unshare_files);
-- 
cgit v1.2.3


From fd8328be874f4190a811c58cd4778ec2c74d2c05 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Tue, 22 Apr 2008 05:11:59 -0400
Subject: [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  | 23 +----------------------
 fs/binfmt_misc.c | 18 +-----------------
 fs/binfmt_som.c  | 10 ----------
 fs/exec.c        | 34 ++++++++++++++++++----------------
 kernel/exit.c    |  3 ---
 kernel/fork.c    |  2 --
 6 files changed, 20 insertions(+), 70 deletions(-)

(limited to 'kernel')

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 5e1a4fb5cacb..9924581df6f6 100644
--- a/fs/binfmt_elf.c
+++ b/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 @@ out_free_interp:
 	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;
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index b53c7e5f41bb..dbf0ac0523de 100644
--- a/fs/binfmt_misc.c
+++ b/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 @@ _error:
 		sys_close(fd_binary);
 	bprm->interp_flags = 0;
 	bprm->interp_data = 0;
-_unshare:
-	if (files)
-		reset_files_struct(current, files);
 	goto _ret;
 }
 
diff --git a/fs/binfmt_som.c b/fs/binfmt_som.c
index 14c63527c762..fdc36bfd6a7b 100644
--- a/fs/binfmt_som.c
+++ b/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;
diff --git a/fs/exec.c b/fs/exec.c
index 54a0a557b678..475543002f13 100644
--- a/fs/exec.c
+++ b/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 @@ out_file:
 out_kfree:
 	kfree(bprm);
 
+out_files:
+	if (files)
+		reset_files_struct(current, files);
 out_ret:
 	return retval;
 }
diff --git a/kernel/exit.c b/kernel/exit.c
index cece89f80ab4..3d320003cc03 100644
--- a/kernel/exit.c
+++ b/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)
 {
diff --git a/kernel/fork.c b/kernel/fork.c
index 76f05a08062b..2fc11f2e2b21 100644
--- a/kernel/fork.c
+++ b/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;
-- 
cgit v1.2.3


From 3b1253880b7a9e6db54b943b2d40bcf2202f58ab Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Tue, 22 Apr 2008 05:31:30 -0400
Subject: [PATCH] sanitize unshare_files/reset_files_struct

* let unshare_files() give caller the displaced files_struct
* don't bother with grabbing reference only to drop it in the
  caller if it hadn't been shared in the first place
* in that form unshare_files() is trivially implemented via
  unshare_fd(), so we eliminate the duplicate logics in fork.c
* reset_files_struct() is not just only called for current;
  it will break the system if somebody ever calls it for anything
  else (we can't modify ->files of somebody else).  Lose the
  task_struct * argument.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/exec.c            | 18 ++++++------------
 include/linux/file.h |  3 ++-
 include/linux/fs.h   |  3 ---
 kernel/exit.c        |  3 ++-
 kernel/fork.c        | 54 +++++++++++++++++++++++-----------------------------
 5 files changed, 34 insertions(+), 47 deletions(-)

(limited to 'kernel')

diff --git a/fs/exec.c b/fs/exec.c
index 475543002f13..b152029f18f6 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1269,19 +1269,13 @@ int do_execve(char * filename,
 	struct linux_binprm *bprm;
 	struct file *file;
 	unsigned long env_p;
-	struct files_struct *files;
+	struct files_struct *displaced;
 	int retval;
 
-	files = current->files;
-	retval = unshare_files();
+	retval = unshare_files(&displaced);
 	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)
@@ -1340,8 +1334,8 @@ int do_execve(char * filename,
 		security_bprm_free(bprm);
 		acct_update_integrals(current);
 		kfree(bprm);
-		if (files)
-			put_files_struct(files);
+		if (displaced)
+			put_files_struct(displaced);
 		return retval;
 	}
 
@@ -1363,8 +1357,8 @@ out_kfree:
 	kfree(bprm);
 
 out_files:
-	if (files)
-		reset_files_struct(current, files);
+	if (displaced)
+		reset_files_struct(displaced);
 out_ret:
 	return retval;
 }
diff --git a/include/linux/file.h b/include/linux/file.h
index 653477021e4c..69baf5a4f0a5 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -117,7 +117,8 @@ struct task_struct;
 
 struct files_struct *get_files_struct(struct task_struct *);
 void put_files_struct(struct files_struct *fs);
-void reset_files_struct(struct task_struct *, struct files_struct *);
+void reset_files_struct(struct files_struct *);
+int unshare_files(struct files_struct **);
 
 extern struct kmem_cache *files_cachep;
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ad41d0bbcb4d..e057438a05ad 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2033,9 +2033,6 @@ static inline ino_t parent_ino(struct dentry *dentry)
 	return res;
 }
 
-/* kernel/fork.c */
-extern int unshare_files(void);
-
 /* Transaction based IO helpers */
 
 /*
diff --git a/kernel/exit.c b/kernel/exit.c
index 3d320003cc03..97f609f574b1 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -507,8 +507,9 @@ void put_files_struct(struct files_struct *files)
 	}
 }
 
-void reset_files_struct(struct task_struct *tsk, struct files_struct *files)
+void reset_files_struct(struct files_struct *files)
 {
+	struct task_struct *tsk = current;
 	struct files_struct *old;
 
 	old = tsk->files;
diff --git a/kernel/fork.c b/kernel/fork.c
index 2fc11f2e2b21..efb618fc8ffe 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -840,36 +840,6 @@ static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
 	return 0;
 }
 
-/*
- *	Helper to unshare the files of the current task.
- *	We don't want to expose copy_files internals to
- *	the exec layer of the kernel.
- */
-
-int unshare_files(void)
-{
-	struct files_struct *files  = current->files;
-	struct files_struct *newf;
-	int error = 0;
-
-	BUG_ON(!files);
-
-	/* This can race but the race causes us to copy when we don't
-	   need to and drop the copy */
-	if(atomic_read(&files->count) == 1)
-	{
-		atomic_inc(&files->count);
-		return 0;
-	}
-	newf = dup_fd(files, &error);
-	if (newf) {
-		task_lock(current);
-		current->files = newf;
-		task_unlock(current);
-	}
-	return error;
-}
-
 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
 {
 	struct sighand_struct *sig;
@@ -1807,3 +1777,27 @@ bad_unshare_cleanup_thread:
 bad_unshare_out:
 	return err;
 }
+
+/*
+ *	Helper to unshare the files of the current task.
+ *	We don't want to expose copy_files internals to
+ *	the exec layer of the kernel.
+ */
+
+int unshare_files(struct files_struct **displaced)
+{
+	struct task_struct *task = current;
+	struct files_struct *copy;
+	int error;
+
+	error = unshare_fd(CLONE_FILES, &copy);
+	if (error || !copy) {
+		*displaced = NULL;
+		return error;
+	}
+	*displaced = task->files;
+	task_lock(task);
+	task->files = copy;
+	task_unlock(task);
+	return 0;
+}
-- 
cgit v1.2.3