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unserialized task->files changing

PATCH In review Kirill Korotaev 3 participants 4 messages Aug 8, 2006

Subsystems (2)
VFS exec and binfmt
lore
Share & tools
lore

Kirill Korotaev

author
#0 lore raw

PATCH 1/1 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.

Found during OpenVZ stress testing.

Signed-off-by Pavel Emelianov <[email protected]>
Signed-off-by Kirill Korotaev <[email protected]>
fs/binfmt_elf.c renamed from fs/binfmt_elf.c.fsfix +6 -1
@@ -1027,8 +1027,13 @@ out_free_file:
 	sys_close(elf_exec_fileno);
 out_free_fh:
 	if (files) {
-		put_files_struct(current->files);
+		struct files_struct *old;
+
+		old = current->files;
+		task_lock(current);
 		current->files = files;
+		task_unlock(current);
+		put_files_struct(old);
 	}
 out_free_ph:
 	kfree(elf_phdata);
fs/binfmt_misc.c renamed from fs/binfmt_misc.c.fsfix +6 -1
@@ -216,8 +216,13 @@ _error:
 	bprm->interp_data = 0;
 _unshare:
 	if (files) {
-		put_files_struct(current->files);
+		struct files_struct *old;
+
+		old = current->files;
+		task_lock(current);
 		current->files = files;
+		task_unlock(current);
+		put_files_struct(old);
 	}
 	goto _ret;
 }
fs/exec.c renamed from fs/exec.c.fsfix +5 -2
@@ -865,7 +865,7 @@ int flush_old_exec(struct linux_binprm *
 {
 	char * name;
 	int i, ch, retval;
-	struct files_struct *files;
+	struct files_struct *files, *old;
 	char tcomm[sizeof(current->comm)];
 
 	/*

@@ -946,8 +946,11 @@ int flush_old_exec(struct linux_binprm *
 	return 0;
 
 mmap_failed:
-	put_files_struct(current->files);
+	old = current->files;
+	task_lock(current);
 	current->files = files;
+	task_unlock(current);
+	put_files_struct(old);
 out:
 	return retval;
 }
#1 lore raw
Quoted 3 lines · Kirill Korotaev

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.

This is three times the exact same code sequence, it should probably go into a helper:

void reset_current_files(struct files_struct *files)

{
	struct files_struct *old = current->files;

	task_lock(current);
	current->files = files;
	task_unlock(current);
	put_files_struct(old);
}
#2 lore raw
Quoted 9 lines · Christoph Hellwig
Quoted 3 lines · Kirill Korotaev

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.

This is three times the exact same code sequence, it should probably go into a helper:

void reset_current_files(struct files_struct *files)

Quoted 8 lines
{
	struct files_struct *old = current->files;

	task_lock(current);
	current->files = files;
	task_unlock(current);
	put_files_struct(old);
}

More over I think you want to task_lock() before reading current->files into 'old'

task_lock(current);
old = current->files;
current->files = files;
task_unlock(current);
put_files_struct(old);

or maybe a xchg() ?

author
#3 lore raw
Quoted 25 lines · Eric Dumazet
Quoted 10 lines · Christoph Hellwig
Quoted 3 lines · Kirill Korotaev

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.

This is three times the exact same code sequence, it should probably go into a helper:

void reset_current_files(struct files_struct *files)

Quoted 8 lines
{
	struct files_struct *old = current->files;

	task_lock(current);
	current->files = files;
	task_unlock(current);
	put_files_struct(old);
}

More over I think you want to task_lock() before reading current->files into 'old'

Quoted 7 lines

task_lock(current);
old = current->files;
current->files = files;
task_unlock(current);
put_files_struct(old);

or maybe a xchg() ?

yeah, never do assignments in declarations :)

BTW, not sure about kthread_exit_files() yet, but looks like it suffers too.

unshare_files() changes current->files w/o locking as well. but I can't see where it puts the old files... hmm...

Kirill