From: Alexander Potapenko glider@google.com Subject: lib/stackdepot.c: fix global out-of-bounds in stack_slabs

Walter Wu has reported a potential case in which init_stack_slab() is called after stack_slabs[STACK_ALLOC_MAX_SLABS - 1] has already been initialized. In that case init_stack_slab() will overwrite stack_slabs[STACK_ALLOC_MAX_SLABS], which may result in a memory corruption.

Link: http://lkml.kernel.org/r/20200218102950.260263-1-glider@google.com Fixes: cd11016e5f521 ("mm, kasan: stackdepot implementation. Enable stackdepot for SLAB") Signed-off-by: Alexander Potapenko glider@google.com Reported-by: Walter Wu walter-zh.wu@mediatek.com Cc: Dmitry Vyukov dvyukov@google.com Cc: Matthias Brugger matthias.bgg@gmail.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Kate Stewart kstewart@linuxfoundation.org Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

lib/stackdepot.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/lib/stackdepot.c~lib-stackdepot-fix-global-out-of-bounds-in-stack_slabs +++ a/lib/stackdepot.c @@ -83,15 +83,19 @@ static bool init_stack_slab(void **preal return true; if (stack_slabs[depot_index] == NULL) { stack_slabs[depot_index] = *prealloc; + *prealloc = NULL; } else { - stack_slabs[depot_index + 1] = *prealloc; + /* If this is the last depot slab, do not touch the next one. */ + if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) { + stack_slabs[depot_index + 1] = *prealloc; + *prealloc = NULL; + } /* * This smp_store_release pairs with smp_load_acquire() from * |next_slab_inited| above and in stack_depot_save(). */ smp_store_release(&next_slab_inited, 1); } - *prealloc = NULL; return true; }

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