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: b6a06cbbb5f7 ("f2fs: support hot file extension")
Signed-off-by: Yongpeng Yang <yangyongpeng@xiaomi.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index 969e06b65b0467f07727e0f2faf736f4fd1a6a4e..12993ae1713b0ad99e67e226cfe96d9ed0818ec4 100644 (file)
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -387,10 +387,12 @@ 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]);
@@ -398,6 +400,7 @@ static ssize_t f2fs_sbi_show(struct f2fs_attr *a,
                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;
        }