mm: nommu: add sysctl_max_map_count() check for do_mmap()

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The sysctl variable vm.max_map_count (sysctl_max_map_count) is not exposed
under !MMU configurations, but its default value (DEFAULT_MAX_MAP_COUNT)
is still used as a allocation limit.  Currently, this limit is enforced
when a VMA entry is split into two chunks (split_vma()), but it is not
checked during initial allocation (do_mmap()).  As a result, if a user
requests a large number of memory allocations, the system will continue
allocating until it hits an Out-Of-Memory (OOM) condition.

This commit introduces a check at the beginning of do_mmap() in nommu.c to
prevent this situation.

This issue was detected using the Linux Test Project (LTP) test linked
below.

Link: https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/munmap/munmap04.c
Link: https://lore.kernel.org/20260702012830.667205-1-thehajime@gmail.com
Signed-off-by: Hajime Tazaki <thehajime@gmail.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

...

This commit is contained in:

Hajime Tazaki 2026-07-02 10:28:30 +09:00 • committed by Andrew Morton

parent 74183a956d

commit 6251d650f4

1 changed files with 3 additions and 0 deletions

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mm/nommu.c

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