7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Josef Bacik [ Upstream commit aa09311c40f6d3aa6037065e17d257ffa48b9402 ] Patch series "mm: various (urgent?) fixes", v1. Here are various MM fixes. The majority was reported by Josef at Anthrophic, the remainder was found while reviewing/overhauling them. Two issues/fixes reported are not included, as we are discussing (better) alternatives on the list already. I left most of the original commit messages as schloppy as they are: I don't particularly care as long as the code is in good shape and as long as they are not actively wrong. But I (and Mike) could not be stopped from overhauling at least some of them. While I don't think there is anything too critical in here, I think this is a good opportunity to see how fast we can get pre-screened/pre-reviewed fixes upstream that might be security-related. The majority are hugetlb + uffd issues, that are not actually that relevant for most installations. But all things that should just get fixed. Some uffd fixes need proper follow ups to fix some more of the root causes of leftover UFFD PTE bits (or proof that there are none remaining). This patch (of 10): When an accountable mapping replaces existing mappings (MAP_FIXED), __mmap_setup() only charges the difference between the size of the new mapping and the VM_ACCOUNT pages it replaces. It then zeroes vms->nr_accounted so that unmapping the old VMAs does not return their charge, which now backs the new mapping. If the operation fails after that point, the error path returns map->charged, i.e. only the difference. By then vms_clean_up_area() has zapped the page tables and closed the old VMAs, so vms_abort_munmap_vmas() cannot reattach them. It leaves a gap and finishes the unmap with vms_complete_munmap_vmas(), which uncharges vms->nr_accounted == 0 pages. The old VMAs are gone, the new one was never created, and the charge of the old ones is never returned, not even when the process exits. No privilege is needed to hit this, only a file whose mmap hook fails, for example a socket (sock_no_mmap() returns -ENODEV): p = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); mmap(p, len, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_FIXED, socket_fd, 0); Every iteration adds len to Committed_AS for good. With vm.overcommit_memory=2 this lets any user make all further accountable allocations in the system fail with -ENOMEM. Once the new mapping has taken over the charge of the mappings it replaces, it owns the charge for all of its pages. Record that in map->charged, so that the error path returns all of it. A failure in __mmap_setup() itself is not affected: it happens before the charge is taken over and the old VMAs are reattached with their charge intact. Original fix generated by an LLM and sent in private by Josef. [david@kernel.org: call variable "uncharged" and make it const, adjust/simplify comments] Link: https://lore.kernel.org/20261015-urgent_fixes-v1-0-42796911043b@kernel.org Link: https://lore.kernel.org/20261015-urgent_fixes-v1-1-42796911043b@kernel.org Fixes: 4f87153e82c4 ("mm: change failure of MAP_FIXED to restoring the gap on failure") Signed-off-by: Josef Bacik Signed-off-by: David Hildenbrand (Arm) Signed-off-by: Andrew Morton Reviewed-by: Lorenzo Stoakes (ARM) Reviewed-by: Pedro Falcato Reviewed-by: Jose A. Perez de Azpillaga Reviewed-by: Lance Yang Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Jann Horn Cc: Muchun Song Cc: Oscar Salvador Cc: Miaohe Lin Cc: Naoya Horiguchi Cc: Adam Litke Cc: Mel Gorman Cc: Rik van Riel Cc: Peter Xu Cc: Kiryl Shutsemau Cc: Mike Rapoport Cc: Signed-off-by: Sasha Levin --- mm/vma.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/mm/vma.c b/mm/vma.c index 6c35f0d775ab6..81e2c93a1cc52 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -2577,14 +2577,17 @@ static int __mmap_setup(struct mmap_state *map, struct vm_area_desc *desc, /* Private writable mapping: check memory availability. */ if (accountable_mapping(map)) { - map->charged = map->pglen; - map->charged -= vms->nr_accounted; - if (map->charged) { - error = security_vm_enough_memory_mm(map->mm, map->charged); + const unsigned long uncharged = map->pglen - vms->nr_accounted; + + /* Charge only what's not already charged by mappings we replace. */ + if (uncharged) { + error = security_vm_enough_memory_mm(map->mm, uncharged); if (error) return error; } + /* Our new mapping owns the entire charge now. */ + map->charged = map->pglen; vms->nr_accounted = 0; vma_flags_set(&map->vma_flags, VMA_ACCOUNT_BIT); } -- 2.53.0