The patch titled Subject: mm: fix off-by-one error in VMA count limit checks has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-fix-off-by-one-error-in-vma-count-limit-checks.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------ From: Kalesh Singh kaleshsingh@google.com Subject: mm: fix off-by-one error in VMA count limit checks Date: Mon, 15 Sep 2025 09:36:32 -0700
The VMA count limit check in do_mmap() and do_brk_flags() uses a strict inequality (>), which allows a process's VMA count to exceed the configured sysctl_max_map_count limit by one.
A process with mm->map_count == sysctl_max_map_count will incorrectly pass this check and then exceed the limit upon allocation of a new VMA when its map_count is incremented.
Other VMA allocation paths, such as split_vma(), already use the correct, inclusive (>=) comparison.
Fix this bug by changing the comparison to be inclusive in do_mmap() and do_brk_flags(), bringing them in line with the correct behavior of other allocation paths.
Link: https://lkml.kernel.org/r/20250915163838.631445-2-kaleshsingh@google.com Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Kalesh Singh kaleshsingh@google.com Cc: David Hildenbrand david@redhat.com Cc: "Liam R. Howlett" Liam.Howlett@oracle.com Cc: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: Mike Rapoport rppt@kernel.org Cc: Minchan Kim minchan@kernel.org Cc: Pedro Falcato pfalcato@suse.de Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/mmap.c | 2 +- mm/vma.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
--- a/mm/mmap.c~mm-fix-off-by-one-error-in-vma-count-limit-checks +++ a/mm/mmap.c @@ -374,7 +374,7 @@ unsigned long do_mmap(struct file *file, return -EOVERFLOW;
/* Too many mappings? */ - if (mm->map_count > sysctl_max_map_count) + if (mm->map_count >= sysctl_max_map_count) return -ENOMEM;
/* --- a/mm/vma.c~mm-fix-off-by-one-error-in-vma-count-limit-checks +++ a/mm/vma.c @@ -2772,7 +2772,7 @@ int do_brk_flags(struct vma_iterator *vm if (!may_expand_vm(mm, vm_flags, len >> PAGE_SHIFT)) return -ENOMEM;
- if (mm->map_count > sysctl_max_map_count) + if (mm->map_count >= sysctl_max_map_count) return -ENOMEM;
if (security_vm_enough_memory_mm(mm, len >> PAGE_SHIFT)) _
Patches currently in -mm which might be from kaleshsingh@google.com are
mm-fix-off-by-one-error-in-vma-count-limit-checks.patch