mm/mremap: correctly uncharge accountable VMAs in error path

The mremap error path is a fragile and unwieldy beast - it reverses the
page table move then updates vma_remap_struct state to swap VMA, length and
address between old and new VMAs in copy_vma_and_data().

If the mremap() operation didn't specify MREMAP_DONTUNMAP then its caller,
move_vma(), invokes unmap_source_vma(), which unmaps the new VMA rather
than the old one.

For accountable VMAs when MREMAP_DONTUNMAP is not specified,
unmap_source_vma() unsets VMA_ACCOUNT_BIT during this unmap in order that
only the delta of a VMA expansion is charged (performed by
vrm_calc_charge() earlier).

Therefore nothing uncharges the expanded VMA size, and there is a permanent
leak in global Committed_AS.

Resolve the issue by uncharging when MREMAP_DONTUNMAP is not specified.

Link: https://lore.kernel.org/20261019-other-mremap-charge-leak-v1-1-d94477fe6545@kernel.org
Fixes: fdbef6149135 ("mm/mremap: don't account pages in vma_to_resize()")
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: <stable@vger.kernel.org>

0 files changed, 0 insertions, 0 deletions