In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
btrfs: reject free space cache with more entries than pages<\/p>\n
When loading a v1 free space cache, __load_free_space_cache() takes
\nnum_entries and num_bitmaps straight from the on-disk
\nbtrfs_free_space_header. That header is stored in the tree_root under a key
\nwith type 0, which the tree-checker has no case for, so neither count is
\nvalidated before the load trusts it.<\/p>\n
The load loops num_entries times and maps the next page whenever the current
\none runs out, going through io_ctl_check_crc() -> io_ctl_map_page(), which
\ndoes io_ctl->pages[io_ctl->index++]. But pages[] is allocated in
\nio_ctl_init() from the cache inode’s i_size, not from num_entries:<\/p>\n
\tnum_pages = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
\n\tio_ctl->pages = kcalloc(num_pages, sizeof(struct page *), GFP_NOFS);<\/p>\n
So if num_entries claims more records than the pages can hold, io_ctl->index
\nruns off the end of pages[]. The write side never hits this because
\nio_ctl_add_entry() and io_ctl_add_bitmap() both stop once
\nio_ctl->index >= io_ctl->num_pages; the read side just never had the same
\ncheck.<\/p>\n
To trigger it, take a clean cache (num_entries = here), set num_entries
\nin the header to 0x10000, and fix up the leaf checksum so it still passes
\nthe tree-checker. The cache inode has i_size = 65536, so num_pages is 16 and
\npages[] is a 16-pointer (kmalloc-128) array. The load now tries to read
\n65536 entries, io_ctl->index walks up to 16, and pages[16] is read past the
\narray:<\/p>\n
BUG: KASAN: slab-out-of-bounds in io_ctl_check_crc (fs\/btrfs\/free-space-cache.c:420 fs\/btrfs\/free-space-cache.c:565)
\n Read of size 8 at addr ffff88800c833a80 by task kworker\/u8:3\/58
\n io_ctl_check_crc (fs\/btrfs\/free-space-cache.c:420 fs\/btrfs\/free-space-cache.c:565)
\n __load_free_space_cache (fs\/btrfs\/free-space-cache.c:655 fs\/btrfs\/free-space-cache.c:820)
\n load_free_space_cache (fs\/btrfs\/free-space-cache.c:1017)
\n caching_thread (fs\/btrfs\/block-group.c:880)
\n btrfs_work_helper (fs\/btrfs\/async-thread.c:312)
\n process_one_work
\n worker_thread
\n kthread
\n ret_from_fork<\/p>\n
free-space-cache.c:420 is io_ctl_map_page(), inlined into io_ctl_check_crc()
\nat line 565, which is why that is the frame KASAN names. The out-of-bounds
\nslot is then treated as a struct page and handed to crc32c(), so the bad
\nread turns into a GP fault.<\/p>\n
Add the missing check to io_ctl_check_crc(), which is where both the entry
\nloop and the bitmap loop end up. When num_entries is too large the load now
\nfails like any corrupt cache: __load_free_space_cache() drops it and rebuilds
\nthe free space from the extent tree, so a valid cache is never rejected.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
btrfs: reject free space cache with more entries than pages<\/p>\n
When loading a v1 free space cache, __load_free_space_cache() takes
\nnu<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-4647","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/4647","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4647"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4647"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4647"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}