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Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Sep 15, 2025 at 09:36:32AM -0700, Kalesh Singh wrote: > 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. Nice spot :) And also 'doh!' > > 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. > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Cc: > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: "Liam R. Howlett" > Cc: Lorenzo Stoakes > Cc: Mike Rapoport > Cc: Minchan Kim > Cc: Pedro Falcato > Signed-off-by: Kalesh Singh LGTM, so: Reviewed-by: Lorenzo Stoakes > --- > > Chnages in v2: > - Fix mmap check, per Pedro > > mm/mmap.c | 2 +- > mm/vma.c | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 7306253cc3b5..e5370e7fcd8f 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -374,7 +374,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr, > return -EOVERFLOW; > > /* Too many mappings? */ > - if (mm->map_count > sysctl_max_map_count) > + if (mm->map_count >= sysctl_max_map_count) > return -ENOMEM; > > /* > diff --git a/mm/vma.c b/mm/vma.c > index 3b12c7579831..033a388bc4b1 100644 > --- a/mm/vma.c > +++ b/mm/vma.c > @@ -2772,7 +2772,7 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma, > 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)) > -- > 2.51.0.384.g4c02a37b29-goog >