Affected: Linux

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

ntfs: avoid stale runlist element dereference in fallocate

ntfs_attr_fallocate() allocates holes and delayed allocations inside initialized size by looking up the current runlist element under ni->runlist.lock. The returned struct runlist_element is only a borrowed pointer into ni->runlist.rl. A writer can replace and free that array after the read lock is dropped, so later reads of rl->lcn, rl->length and rl->vcn can touch freed memory.

The buggy scenario involves two paths, with each column showing the order within that path:

ntfs_attr_fallocate(): 1. Take ni->runlist.lock for read. 2. Get rl from ntfs_attr_find_vcn_nolock(). 3. Drop ni->runlist.lock. 4. Read rl->lcn, rl->length and rl->vcn.

mmap page_mkwrite: 1. Enter ntfs_filemap_page_mkwrite(). 2. Reach __ntfs_write_iomap_begin() and ntfs_attr_map_cluster(). 3. Merge allocation state with ntfs_runlists_merge(). 4. Reallocate ni->runlist.rl in ntfs_rl_realloc(), freeing the old array.

Validation reproduced this kernel report: BUG: KASAN: slab-use-after-free in ntfs_attr_fallocate+0xbb8/0xd00

Call Trace: <TASK> dump_stack_lvl+0x66/0xa0 print_report+0xce/0x630 ? ntfs_attr_fallocate+0xbb8/0xd00 ? srso_alias_return_thunk+0x5/0xfbef5 ? __virt_addr_valid+0x20d/0x410 ? ntfs_attr_fallocate+0xbb8/0xd00 kasan_report+0xe0/0x110 ? ntfs_attr_fallocate+0xbb8/0xd00 ntfs_attr_fallocate+0xbb8/0xd00 ? lock_acquire+0x2b8/0x2f0 ? __pfx_ntf…