In the Linux kernel, the following vulnerability has been resolved: f2fs: fix node_cnt race...

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix node_cnt race between extent node destroy and writeback

f2fs_destroy_extent_node() does not set FI_NO_EXTENT before clearing extent nodes. When called from f2fs_drop_inode() with I_SYNC set, concurrent kworker writeback can insert new extent nodes into the same extent tree, racing with the destroy and triggering f2fs_bug_on() in __destroy_extent_node(). The scenario is as follows:

drop inode writeback

• iput
• f2fs_drop_inode // I_SYNC set
• f2fs_destroy_extent_node - __destroy_extent_node
  • while (node_cnt) { write_lock(&et->lock) __free_extent_tree write_unlock(&et->lock) - __writeback_single_inode - f2fs_outplace_write_data - f2fs_update_read_extent_cache - __update_extent_tree_range // FI_NO_EXTENT not set, // insert new extent node } // node_cnt == 0, exit while
  • f2fs_bug_on(node_cnt) // node_cnt > 0

Additionally, __update_extent_tree_range() only checks FI_NO_EXTENT for EX_READ type, leaving EX_BLOCK_AGE updates completely unprotected.

This patch set FI_NO_EXTENT under et->lock in __destroy_extent_node(), consistent with other callers (__update_extent_tree_range and __drop_extent_tree) and check FI_NO_EXTENT for both EX_READ and EX_BLOCK_AGE tree.