CVE - CVE-2024-26960

CVE-ID
CVE-2024-26960	Learn more at National Vulnerability Database (NVD) • CVSS Severity Rating • Fix Information • Vulnerable Software Versions • SCAP Mappings • CPE Information
Description
In the Linux kernel, the following vulnerability has been resolved: mm: swap: fix race between free_swap_and_cache() and swapoff() There was previously a theoretical window where swapoff() could run and teardown a swap_info_struct while a call to free_swap_and_cache() was running in another thread. This could cause, amongst other bad possibilities, swap_page_trans_huge_swapped() (called by free_swap_and_cache()) to access the freed memory for swap_map. This is a theoretical problem and I haven't been able to provoke it from a test case. But there has been agreement based on code review that this is possible (see link below). Fix it by using get_swap_device()/put_swap_device(), which will stall swapoff(). There was an extra check in _swap_info_get() to confirm that the swap entry was not free. This isn't present in get_swap_device() because it doesn't make sense in general due to the race between getting the reference and swapoff. So I've added an equivalent check directly in free_swap_and_cache(). Details of how to provoke one possible issue (thanks to David Hildenbrand for deriving this): --8<----- __swap_entry_free() might be the last user and result in "count == SWAP_HAS_CACHE". swapoff->try_to_unuse() will stop as soon as soon as si->inuse_pages==0. So the question is: could someone reclaim the folio and turn si->inuse_pages==0, before we completed swap_page_trans_huge_swapped(). Imagine the following: 2 MiB folio in the swapcache. Only 2 subpages are still references by swap entries. Process 1 still references subpage 0 via swap entry. Process 2 still references subpage 1 via swap entry. Process 1 quits. Calls free_swap_and_cache(). -> count == SWAP_HAS_CACHE [then, preempted in the hypervisor etc.] Process 2 quits. Calls free_swap_and_cache(). -> count == SWAP_HAS_CACHE Process 2 goes ahead, passes swap_page_trans_huge_swapped(), and calls __try_to_reclaim_swap(). __try_to_reclaim_swap()->folio_free_swap()->delete_from_swap_cache()-> put_swap_folio()->free_swap_slot()->swapcache_free_entries()-> swap_entry_free()->swap_range_free()-> ... WRITE_ONCE(si->inuse_pages, si->inuse_pages - nr_entries); What stops swapoff to succeed after process 2 reclaimed the swap cache but before process1 finished its call to swap_page_trans_huge_swapped()? --8<-----
References
Note: References are provided for the convenience of the reader to help distinguish between vulnerabilities. The list is not intended to be complete.
MISC:https://git.kernel.org/stable/c/0f98f6d2fb5fad00f8299b84b85b6bc1b6d7d19a URL:https://git.kernel.org/stable/c/0f98f6d2fb5fad00f8299b84b85b6bc1b6d7d19a MISC:https://git.kernel.org/stable/c/1ede7f1d7eed1738d1b9333fd1e152ccb450b86a URL:https://git.kernel.org/stable/c/1ede7f1d7eed1738d1b9333fd1e152ccb450b86a MISC:https://git.kernel.org/stable/c/2da5568ee222ce0541bfe446a07998f92ed1643e URL:https://git.kernel.org/stable/c/2da5568ee222ce0541bfe446a07998f92ed1643e MISC:https://git.kernel.org/stable/c/363d17e7f7907c8e27a9e86968af0eaa2301787b URL:https://git.kernel.org/stable/c/363d17e7f7907c8e27a9e86968af0eaa2301787b MISC:https://git.kernel.org/stable/c/3ce4c4c653e4e478ecb15d3c88e690f12cbf6b39 URL:https://git.kernel.org/stable/c/3ce4c4c653e4e478ecb15d3c88e690f12cbf6b39 MISC:https://git.kernel.org/stable/c/82b1c07a0af603e3c47b906c8e991dc96f01688e URL:https://git.kernel.org/stable/c/82b1c07a0af603e3c47b906c8e991dc96f01688e MISC:https://git.kernel.org/stable/c/d85c11c97ecf92d47a4b29e3faca714dc1f18d0d URL:https://git.kernel.org/stable/c/d85c11c97ecf92d47a4b29e3faca714dc1f18d0d
Assigning CNA
kernel.org
Date Record Created
20240219	Disclaimer: The record creation date may reflect when the CVE ID was allocated or reserved, and does not necessarily indicate when this vulnerability was discovered, shared with the affected vendor, publicly disclosed, or updated in CVE.
Phase (Legacy)
Assigned (20240219)
Votes (Legacy)

Comments (Legacy)

Proposed (Legacy)
N/A
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