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([2601:647:4000:1108:a155:f521:af71:d5a4]) by smtp.gmail.com with ESMTPSA id z29sm9763651pge.21.2019.12.19.18.57.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Dec 2019 18:57:15 -0800 (PST) Subject: Re: [PATCH] locking/lockdep: Fix potential buffer overrun problem in stack_trace[] To: Waiman Long , Peter Zijlstra , Ingo Molnar , Will Deacon Cc: linux-kernel@vger.kernel.org References: <20191219182812.20191-1-longman@redhat.com> From: Bart Van Assche Autocrypt: addr=bvanassche@acm.org; prefer-encrypt=mutual; keydata= mQENBFSOu4oBCADcRWxVUvkkvRmmwTwIjIJvZOu6wNm+dz5AF4z0FHW2KNZL3oheO3P8UZWr LQOrCfRcK8e/sIs2Y2D3Lg/SL7qqbMehGEYcJptu6mKkywBfoYbtBkVoJ/jQsi2H0vBiiCOy fmxMHIPcYxaJdXxrOG2UO4B60Y/BzE6OrPDT44w4cZA9DH5xialliWU447Bts8TJNa3lZKS1 AvW1ZklbvJfAJJAwzDih35LxU2fcWbmhPa7EO2DCv/LM1B10GBB/oQB5kvlq4aA2PSIWkqz4 3SI5kCPSsygD6wKnbRsvNn2mIACva6VHdm62A7xel5dJRfpQjXj2snd1F/YNoNc66UUTABEB AAG0JEJhcnQgVmFuIEFzc2NoZSA8YnZhbmFzc2NoZUBhY20ub3JnPokBOQQTAQIAIwUCVI67 igIbAwcLCQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJEHFcPTXFzhAJ8QkH/1AdXblKL65M Y1Zk1bYKnkAb4a98LxCPm/pJBilvci6boefwlBDZ2NZuuYWYgyrehMB5H+q+Kq4P0IBbTqTa jTPAANn62A6jwJ0FnCn6YaM9TZQjM1F7LoDX3v+oAkaoXuq0dQ4hnxQNu792bi6QyVdZUvKc macVFVgfK9n04mL7RzjO3f+X4midKt/s+G+IPr4DGlrq+WH27eDbpUR3aYRk8EgbgGKvQFdD CEBFJi+5ZKOArmJVBSk21RHDpqyz6Vit3rjep7c1SN8s7NhVi9cjkKmMDM7KYhXkWc10lKx2 RTkFI30rkDm4U+JpdAd2+tP3tjGf9AyGGinpzE2XY1K5AQ0EVI67igEIAKiSyd0nECrgz+H5 PcFDGYQpGDMTl8MOPCKw/F3diXPuj2eql4xSbAdbUCJzk2ETif5s3twT2ER8cUTEVOaCEUY3 eOiaFgQ+nGLx4BXqqGewikPJCe+UBjFnH1m2/IFn4T9jPZkV8xlkKmDUqMK5EV9n3eQLkn5g lco+FepTtmbkSCCjd91EfThVbNYpVQ5ZjdBCXN66CKyJDMJ85HVr5rmXG/nqriTh6cv1l1Js T7AFvvPjUPknS6d+BETMhTkbGzoyS+sywEsQAgA+BMCxBH4LvUmHYhpS+W6CiZ3ZMxjO8Hgc ++w1mLeRUvda3i4/U8wDT3SWuHcB3DWlcppECLkAEQEAAYkBHwQYAQIACQUCVI67igIbDAAK CRBxXD01xc4QCZ4dB/0QrnEasxjM0PGeXK5hcZMT9Eo998alUfn5XU0RQDYdwp6/kMEXMdmT oH0F0xB3SQ8WVSXA9rrc4EBvZruWQ+5/zjVrhhfUAx12CzL4oQ9Ro2k45daYaonKTANYG22y //x8dLe2Fv1By4SKGhmzwH87uXxbTJAUxiWIi1np0z3/RDnoVyfmfbbL1DY7zf2hYXLLzsJR mSsED/1nlJ9Oq5fALdNEPgDyPUerqHxcmIub+pF0AzJoYHK5punqpqfGmqPbjxrJLPJfHVKy goMj5DlBMoYqEgpbwdUYkH6QdizJJCur4icy8GUNbisFYABeoJ91pnD4IGei3MTdvINSZI5e Message-ID: <0cdfb26d-7faa-9da0-05b9-79bb21703283@acm.org> Date: Thu, 19 Dec 2019 18:57:13 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <20191219182812.20191-1-longman@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019-12-19 10:28, Waiman Long wrote: > If the lockdep code is really running out of the stack_trace entries, > there is a possiblity that buffer overrun can happen and corrupt the ^^^^^^^^^^ possibility? > data immediately after stack_trace[]. > > If there is less than LOCK_TRACE_SIZE_IN_LONGS entries left before > the call to save_trace(), the max_entries computation will leave it > with a very large positive number because of its unsigned nature. The > subsequent call to stack_trace_save() will then corrupt the data after > stack_trace[]. Fix that by changing max_entries to a signed integer > and check for negative value before calling stack_trace_save(). > > Fixes: 12593b7467f9 ("locking/lockdep: Reduce space occupied by stack traces") > Signed-off-by: Waiman Long > --- > kernel/locking/lockdep.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > index 32282e7112d3..56e260a7582f 100644 > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -482,7 +482,7 @@ static struct lock_trace *save_trace(void) > struct lock_trace *trace, *t2; > struct hlist_head *hash_head; > u32 hash; > - unsigned int max_entries; > + int max_entries; > > BUILD_BUG_ON_NOT_POWER_OF_2(STACK_TRACE_HASH_SIZE); > BUILD_BUG_ON(LOCK_TRACE_SIZE_IN_LONGS >= MAX_STACK_TRACE_ENTRIES); > @@ -490,10 +490,8 @@ static struct lock_trace *save_trace(void) > trace = (struct lock_trace *)(stack_trace + nr_stack_trace_entries); > max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries - > LOCK_TRACE_SIZE_IN_LONGS; > - trace->nr_entries = stack_trace_save(trace->entries, max_entries, 3); > > - if (nr_stack_trace_entries >= MAX_STACK_TRACE_ENTRIES - > - LOCK_TRACE_SIZE_IN_LONGS - 1) { > + if (max_entries < 0) { > if (!debug_locks_off_graph_unlock()) > return NULL; > > @@ -502,6 +500,7 @@ static struct lock_trace *save_trace(void) > > return NULL; > } > + trace->nr_entries = stack_trace_save(trace->entries, max_entries, 3); > > hash = jhash(trace->entries, trace->nr_entries * > sizeof(trace->entries[0]), 0); I'm not sure whether it is useful to call stack_trace_save() if max_entries == 0. How about changing the "max_entries < 0" test into "max_entries <= 0"? Thanks, Bart.