Linaro-mm-sig April 2024

linaro-mm-sig@lists.linaro.org

18 participants
41 discussions

Re: [PATCH] dmabuf: fix dmabuf file poll uaf issue

by Christian König

Am 27.03.24 um 03:29 schrieb Zhiguo Jiang: > The issue is a UAF issue of dmabuf file fd. Throght debugging, we found > that the dmabuf file fd is added to the epoll event listener list, and > when it is released, it is not removed from the epoll list, which leads > to the UAF(Use-After-Free) issue. As far as I can see that's not because of the DMA-buf code, but because you are somehow using this interface incorrectly. When dma_buf_poll() is called it is mandatory for the caller to hold a reference to the file descriptor on which the poll operation is executed. So adding code like "if (!file_count(file))" in the beginning of dma_buf_poll() is certainly broken. My best guess is that you have some unbalanced dma_buf_get()/dma_buf_put() somewhere instead. Regards, Christian. > > The UAF issue can be solved by checking dmabuf file->f_count value and > skipping the poll operation for the closed dmabuf file in the > dma_buf_poll(). We have tested this solved patch multiple times and > have not reproduced the uaf issue. > > crash dump: > list_del corruption, ffffff8a6f143a90->next is LIST_POISON1 > (dead000000000100) > ------------[ cut here ]------------ > kernel BUG at lib/list_debug.c:55! > Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP > pc : __list_del_entry_valid+0x98/0xd4 > lr : __list_del_entry_valid+0x98/0xd4 > sp : ffffffc01d413d00 > x29: ffffffc01d413d00 x28: 00000000000000c0 x27: 0000000000000020 > x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000080007 > x23: ffffff8b22e5dcc0 x22: ffffff88a6be12d0 x21: ffffff8b22e572b0 > x20: ffffff80254ed0a0 x19: ffffff8a6f143a00 x18: ffffffda5efed3c0 > x17: 6165642820314e4f x16: 53494f505f545349 x15: 4c20736920747865 > x14: 6e3e2d3039613334 x13: 2930303130303030 x12: 0000000000000018 > x11: ffffff8b6c188000 x10: 00000000ffffffff x9 : 6c8413a194897b00 > x8 : 6c8413a194897b00 x7 : 74707572726f6320 x6 : 6c65645f7473696c > x5 : ffffff8b6c3b2a3e x4 : ffffff8b6c3b2a40 x3 : ffff103000001005 > x2 : 0000000000000001 x1 : 00000000000000c0 x0 : 000000000000004e > Call trace: > __list_del_entry_valid+0x98/0xd4 > dma_buf_file_release+0x48/0x90 > __fput+0xf4/0x280 > ____fput+0x10/0x20 > task_work_run+0xcc/0xf4 > do_notify_resume+0x2a0/0x33c > el0_svc+0x5c/0xa4 > el0t_64_sync_handler+0x68/0xb4 > el0t_64_sync+0x1a0/0x1a4 > Code: d0006fe0 912c5000 f2fbd5a2 94231a01 (d4210000) > ---[ end trace 0000000000000000 ]--- > Kernel panic - not syncing: Oops - BUG: Fatal exception > SMP: stopping secondary CPUs > > Signed-off-by: Zhiguo Jiang <justinjiang(a)vivo.com> > --- > drivers/dma-buf/dma-buf.c | 28 ++++++++++++++++++++++++---- > 1 file changed, 24 insertions(+), 4 deletions(-) > mode change 100644 => 100755 drivers/dma-buf/dma-buf.c > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > index 8fe5aa67b167..e469dd9288cc > --- a/drivers/dma-buf/dma-buf.c > +++ b/drivers/dma-buf/dma-buf.c > @@ -240,6 +240,10 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll) > struct dma_resv *resv; > __poll_t events; > > + /* Check if the file exists */ > + if (!file_count(file)) > + return EPOLLERR; > + > dmabuf = file->private_data; > if (!dmabuf || !dmabuf->resv) > return EPOLLERR; > @@ -266,8 +270,15 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll) > spin_unlock_irq(&dmabuf->poll.lock); > > if (events & EPOLLOUT) { > - /* Paired with fput in dma_buf_poll_cb */ > - get_file(dmabuf->file); > + /* > + * Paired with fput in dma_buf_poll_cb, > + * Skip poll for the closed file. > + */ > + if (!get_file_rcu(&dmabuf->file)) { > + events &= ~EPOLLOUT; > + dcb->active = 0; > + goto clear_out_event; > + } > > if (!dma_buf_poll_add_cb(resv, true, dcb)) > /* No callback queued, wake up any other waiters */ > @@ -277,6 +288,7 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll) > } > } > > +clear_out_event: > if (events & EPOLLIN) { > struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_in; > > @@ -289,8 +301,15 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll) > spin_unlock_irq(&dmabuf->poll.lock); > > if (events & EPOLLIN) { > - /* Paired with fput in dma_buf_poll_cb */ > - get_file(dmabuf->file); > + /* > + * Paired with fput in dma_buf_poll_cb, > + * Skip poll for the closed file. > + */ > + if (!get_file_rcu(&dmabuf->file)) { > + events &= ~EPOLLIN; > + dcb->active = 0; > + goto clear_in_event; > + } > > if (!dma_buf_poll_add_cb(resv, false, dcb)) > /* No callback queued, wake up any other waiters */ > @@ -300,6 +319,7 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll) > } > } > > +clear_in_event: > dma_resv_unlock(resv); > return events; > }

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Linaro-mm-sig April 2024