In the Linux kernel, the following vulnerability has been resolved: mm, swap: fix potential UAF issue for VMA readahead Since commit 78524b05f1a3 ("mm, swap: avoid redundant swap device pinning"), the common helper for allocating and preparing a folio in the swap cache layer no longer tries to get a swap device reference internally, because all callers of __read_swap_cache_async are already holding a swap entry reference. The repeated swap device pinning isn't needed on the same swap device. Caller of VMA readahead is also holding a reference to the target entry's swap device, but VMA readahead walks the page table, so it might encounter swap entries from other devices, and call __read_swap_cache_async on another device without holding a reference to it. So it is possible to cause a UAF when swapoff of device A raced with swapin on device B, and VMA readahead tries to read swap entries from device A. It's not easy to trigger, but in theory, it could cause real issues. Make VMA readahead try to get the device reference first if the swap device is a different one from the target entry.

In the Linux kernel, the following vulnerability has been resolved: mm: swap: check for stable address space before operating on the VMA It is possible to hit a zero entry while traversing the vmas in unuse_mm() called from swapoff path and accessing it causes the OOPS: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000446--> Loading the memory from offset 0x40 on the XA_ZERO_ENTRY as address. Mem abort info: ESR = 0x0000000096000005 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 FSC = 0x05: level 1 translation fault The issue is manifested from the below race between the fork() on a process and swapoff: fork(dup_mmap()) swapoff(unuse_mm) --------------- ----------------- 1) Identical mtree is built using __mt_dup(). 2) copy_pte_range()--> copy_nonpresent_pte(): The dst mm is added into the mmlist to be visible to the swapoff operation. 3) Fatal signal is sent to the parent process(which is the current during the fork) thus skip the duplication of the vmas and mark the vma range with XA_ZERO_ENTRY as a marker for this process that helps during exit_mmap(). 4) swapoff is tried on the 'mm' added to the 'mmlist' as part of the 2. 5) unuse_mm(), that iterates through the vma's of this 'mm' will hit the non-NULL zero entry and operating on this zero entry as a vma is resulting into the oops. The proper fix would be around not exposing this partially-valid tree to others when droping the mmap lock, which is being solved with [1]. A simpler solution would be checking for MMF_UNSTABLE, as it is set if mm_struct is not fully initialized in dup_mmap(). Thanks to Liam/Lorenzo/David for all the suggestions in fixing this issue.

In the Linux kernel, the following vulnerability has been resolved: mm/swap: fix swap_info_struct race between swapoff and get_swap_pages() The si->lock must be held when deleting the si from the available list. Otherwise, another thread can re-add the si to the available list, which can lead to memory corruption. The only place we have found where this happens is in the swapoff path. This case can be described as below: core 0 core 1 swapoff del_from_avail_list(si) waiting try lock si->lock acquire swap_avail_lock and re-add si into swap_avail_head acquire si->lock but missing si already being added again, and continuing to clear SWP_WRITEOK, etc. It can be easily found that a massive warning messages can be triggered inside get_swap_pages() by some special cases, for example, we call madvise(MADV_PAGEOUT) on blocks of touched memory concurrently, meanwhile, run much swapon-swapoff operations (e.g. stress-ng-swap). However, in the worst case, panic can be caused by the above scene. In swapoff(), the memory used by si could be kept in swap_info[] after turning off a swap. This means memory corruption will not be caused immediately until allocated and reset for a new swap in the swapon path. A panic message caused: (with CONFIG_PLIST_DEBUG enabled) ------------[ cut here ]------------ top: 00000000e58a3003, n: 0000000013e75cda, p: 000000008cd4451a prev: 0000000035b1e58a, n: 000000008cd4451a, p: 000000002150ee8d next: 000000008cd4451a, n: 000000008cd4451a, p: 000000008cd4451a WARNING: CPU: 21 PID: 1843 at lib/plist.c:60 plist_check_prev_next_node+0x50/0x70 Modules linked in: rfkill(E) crct10dif_ce(E)... CPU: 21 PID: 1843 Comm: stress-ng Kdump: ... 5.10.134+ Hardware name: Alibaba Cloud ECS, BIOS 0.0.0 02/06/2015 pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--) pc : plist_check_prev_next_node+0x50/0x70 lr : plist_check_prev_next_node+0x50/0x70 sp : ffff0018009d3c30 x29: ffff0018009d3c40 x28: ffff800011b32a98 x27: 0000000000000000 x26: ffff001803908000 x25: ffff8000128ea088 x24: ffff800011b32a48 x23: 0000000000000028 x22: ffff001800875c00 x21: ffff800010f9e520 x20: ffff001800875c00 x19: ffff001800fdc6e0 x18: 0000000000000030 x17: 0000000000000000 x16: 0000000000000000 x15: 0736076307640766 x14: 0730073007380731 x13: 0736076307640766 x12: 0730073007380731 x11: 000000000004058d x10: 0000000085a85b76 x9 : ffff8000101436e4 x8 : ffff800011c8ce08 x7 : 0000000000000000 x6 : 0000000000000001 x5 : ffff0017df9ed338 x4 : 0000000000000001 x3 : ffff8017ce62a000 x2 : ffff0017df9ed340 x1 : 0000000000000000 x0 : 0000000000000000 Call trace: plist_check_prev_next_node+0x50/0x70 plist_check_head+0x80/0xf0 plist_add+0x28/0x140 add_to_avail_list+0x9c/0xf0 _enable_swap_info+0x78/0xb4 __do_sys_swapon+0x918/0xa10 __arm64_sys_swapon+0x20/0x30 el0_svc_common+0x8c/0x220 do_el0_svc+0x2c/0x90 el0_svc+0x1c/0x30 el0_sync_handler+0xa8/0xb0 el0_sync+0x148/0x180 irq event stamp: 2082270 Now, si->lock locked before calling 'del_from_avail_list()' to make sure other thread see the si had been deleted and SWP_WRITEOK cleared together, will not reinsert again. This problem exists in versions after stable 5.10.y.

linux

In the Linux kernel, the following vulnerability has been resolved: mm/swapfile: skip HugeTLB pages for unuse_vma I got a bad pud error and lost a 1GB HugeTLB when calling swapoff. The problem can be reproduced by the following steps: 1. Allocate an anonymous 1GB HugeTLB and some other anonymous memory. 2. Swapout the above anonymous memory. 3. run swapoff and we will get a bad pud error in kernel message: mm/pgtable-generic.c:42: bad pud 00000000743d215d(84000001400000e7) We can tell that pud_clear_bad is called by pud_none_or_clear_bad in unuse_pud_range() by ftrace. And therefore the HugeTLB pages will never be freed because we lost it from page table. We can skip HugeTLB pages for unuse_vma to fix it.

linux

In the Linux kernel, the following vulnerability has been resolved: mm: cachestat: fix two shmem bugs When cachestat on shmem races with swapping and invalidation, there are two possible bugs: 1) A swapin error can have resulted in a poisoned swap entry in the shmem inode's xarray. Calling get_shadow_from_swap_cache() on it will result in an out-of-bounds access to swapper_spaces[]. Validate the entry with non_swap_entry() before going further. 2) When we find a valid swap entry in the shmem's inode, the shadow entry in the swapcache might not exist yet: swap IO is still in progress and we're before __remove_mapping; swapin, invalidation, or swapoff have removed the shadow from swapcache after we saw the shmem swap entry. This will send a NULL to workingset_test_recent(). The latter purely operates on pointer bits, so it won't crash - node 0, memcg ID 0, eviction timestamp 0, etc. are all valid inputs - but it's a bogus test. In theory that could result in a false "recently evicted" count. Such a false positive wouldn't be the end of the world. But for code clarity and (future) robustness, be explicit about this case. Bail on get_shadow_from_swap_cache() returning NULL.

linux

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<-----

linux · debian

Multiple buffer overflows in bos.rte.control in IBM AIX 5.2 and 5.3 allow local users to gain privileges via unspecified vectors related to the (1) swap, (2) swapoff, and (3) swapon programs.

ibm