f2fs: protect extension_list reading with sb_lock in f2fs_sbi_show()

In f2fs_sbi_show(), the extension_list, extension_count and
hot_ext_count are read without holding sbi->sb_lock. If a concurrent
sysfs store modifies the extension list via f2fs_update_extension_list(),
the show path may read inconsistent count and array contents, potentially
leading to out-of-bounds access or displaying stale data.

Fix this by holding sb_lock around the entire extension list read
and format operation.

Fixes: b6a06cb ("f2fs: support hot file extension")
Signed-off-by: Yongpeng Yang <[email protected]>
Reviewed-by: Chao Yu <[email protected]>
Signed-off-by: Jaegeuk Kim <[email protected]>

Author: Yongpeng Yang

fs/f2fs/sysfs.c

@@ -387,17 +387,20 @@ static ssize_t f2fs_sbi_show(struct f2fs_attr *a,
 	if (!strcmp(a->attr.name, "extension_list")) {
 		__u8 (*extlist)[F2FS_EXTENSION_LEN] =
 					sbi->raw_super->extension_list;
-		int cold_count = le32_to_cpu(sbi->raw_super->extension_count);
-		int hot_count = sbi->raw_super->hot_ext_count;
+		int cold_count, hot_count;
 		int len = 0, i;
 
+		f2fs_down_read(&sbi->sb_lock);
+		cold_count = le32_to_cpu(sbi->raw_super->extension_count);
+		hot_count = sbi->raw_super->hot_ext_count;
 		len += sysfs_emit_at(buf, len, "cold file extension:\n");
 		for (i = 0; i < cold_count; i++)
 			len += sysfs_emit_at(buf, len, "%s\n", extlist[i]);
 
 		len += sysfs_emit_at(buf, len, "hot file extension:\n");
 		for (i = cold_count; i < cold_count + hot_count; i++)
 			len += sysfs_emit_at(buf, len, "%s\n", extlist[i]);
+		f2fs_up_read(&sbi->sb_lock);
 
 		return len;
 	}