trace: f2fs: Fix kasan slab-out-of-bounds

This patch fixes the following KASAN report:

KASAN: slab-out-of-bounds in string+0xb4/0x120
Read of size 1 at addr fffffffbf2f3b510 by task atrace/9219

Call trace:
dump_backtrace+0x0/0x3e8
show_stack+0x20/0x30
dump_stack+0x13c/0x198
print_address_description+0x80/0x2e0
kasan_report_error+0x1ac/0x210
__asan_report_load2_noabort+0x0/0xb8
string+0xb4/0x120
vsnprintf+0x5f4/0x1658
seq_buf_vprintf+0x11c/0x200
trace_seq_printf+0x1a8/0x320
trace_raw_output_f2fs_lookup_start+0xe8/0x158
print_trace_line+0x3cc/0xeb0
s_show+0x154/0x248
seq_read+0x8a8/0x1378
__vfs_read+0xfc/0x550
vfs_read+0x108/0x268
ksys_read+0x124/0x2b0

Correctly assign name string for f2fs trace.

Change-Id: I8ed0cf7c542ead06479fb4fde65b01b5e739e6db
Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>
Signed-off-by: engstk <eng.stk@sapo.pt>

include/trace/events/f2fs.h

@@ -333,23 +333,23 @@ TRACE_EVENT(f2fs_unlink_enter,
 		__field(ino_t,	ino)
 		__field(loff_t,	size)
 		__field(blkcnt_t, blocks)
-		__field(const char *,	name)
+		__string(name, dentry->d_name.name)
 	),
 
 	TP_fast_assign(
 		__entry->dev	= dir->i_sb->s_dev;
 		__entry->ino	= dir->i_ino;
 		__entry->size	= dir->i_size;
 		__entry->blocks	= dir->i_blocks;
-		__entry->name	= dentry->d_name.name;
+		__assign_str(name, dentry->d_name.name);
 	),
 
 	TP_printk("dev = (%d,%d), dir ino = %lu, i_size = %lld, "
 		"i_blocks = %llu, name = %s",
 		show_dev_ino(__entry),
 		__entry->size,
 		(unsigned long long)__entry->blocks,
-		__entry->name)
+		__get_str(name))
 );
 
 DEFINE_EVENT(f2fs__inode_exit, f2fs_unlink_exit,
@@ -810,20 +810,20 @@ TRACE_EVENT(f2fs_lookup_start,
 	TP_STRUCT__entry(
 		__field(dev_t,	dev)
 		__field(ino_t,	ino)
-		__field(const char *,	name)
+		__string(name, dentry->d_name.name)
 		__field(unsigned int, flags)
 	),
 
 	TP_fast_assign(
 		__entry->dev	= dir->i_sb->s_dev;
 		__entry->ino	= dir->i_ino;
-		__entry->name	= dentry->d_name.name;
+		__assign_str(name, dentry->d_name.name);
 		__entry->flags	= flags;
 	),
 
 	TP_printk("dev = (%d,%d), pino = %lu, name:%s, flags:%u",
 		show_dev_ino(__entry),
-		__entry->name,
+		__get_str(name),
 		__entry->flags)
 );
 
@@ -837,22 +837,22 @@ TRACE_EVENT(f2fs_lookup_end,
 	TP_STRUCT__entry(
 		__field(dev_t,	dev)
 		__field(ino_t,	ino)
-		__field(const char *,	name)
+		__string(name, dentry->d_name.name)
 		__field(nid_t,	cino)
 		__field(int,	err)
 	),
 
 	TP_fast_assign(
 		__entry->dev	= dir->i_sb->s_dev;
 		__entry->ino	= dir->i_ino;
-		__entry->name	= dentry->d_name.name;
+		__assign_str(name, dentry->d_name.name);
 		__entry->cino	= ino;
 		__entry->err	= err;
 	),
 
 	TP_printk("dev = (%d,%d), pino = %lu, name:%s, ino:%u, err:%d",
 		show_dev_ino(__entry),
-		__entry->name,
+		__get_str(name),
 		__entry->cino,
 		__entry->err)
 );