Messages in this thread | | | From | Dongliang Mu <> | Date | Wed, 21 Jul 2021 12:44:09 +0800 | Subject | Re: Doubts about Patch "ipack/carriers/tpci200: Fix a double free in tpci200_pci_probe" |
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On Tue, Jul 20, 2021 at 10:38 PM <lyl2019@mail.ustc.edu.cn> wrote: > > > Hello Dongliang Mu, > > > Depending on if CONFIG_PCI defines, the "tpci200->info->cfg_regs" may > > not be freed. > > > > #ifdef CONFIG_PCI > > /* Destroy a virtual mapping cookie for a PCI BAR (memory or IO) */ > > struct pci_dev; > > extern void pci_iounmap(struct pci_dev *dev, void __iomem *); > > #elif defined(CONFIG_GENERIC_IOMAP) > > struct pci_dev; > > static inline void pci_iounmap(struct pci_dev *dev, void __iomem *addr) > > { } > > #endif > > I think only `CONFIG_PCI=n` and `CONFIG_GENERIC_IOMAP=y` cause pci_iounmap an empty > implementation. Actually, `CONFIG_PCI` is a default option when run `make defconfig`, > pci_iounmap() usually is acted as an extern function.
I see. From the discussion with other developers, the usage of this driver needs to enable CONFIG_PCI. So we may not worry about this point any more.
> > > > Even if CONFIG_PCI is undefined, it is possible that > > tpci200->info->cfg_regs is not freed at all. Therefore, this patch > > would cause memory leak. Take a look at the following code: > > > > void pci_iounmap(struct pci_dev *dev, void __iomem * addr) > > { > > IO_COND(addr, /* nothing */, iounmap(addr)); > > } > > Here i am not sure this is the final implementation of pci_iounmap(), > because pci_iounmap() is re-implementated in many architectures. > Even so, i observed there still many call-sites of pci_iounmap() have reset > `the addr = NULL` after calling. > Can you have some ways to determine the actual implementation of > pci_iounmap in our cases?
Yeah, that's the problem. I am not highly certain about the implementation of this function. So if the free is not done, your previous patch would cause a memory leak.
> > > > #define IO_COND(addr, is_pio, is_mmio) do { \ > > unsigned long port = (unsigned long __force)addr; \ > > if (port >= PIO_RESERVED) { \ > > is_mmio; \ > > } else if (port > PIO_OFFSET) { \ > > port &= PIO_MASK; \ > > is_pio; \ > > } else \ > > bad_io_access(port, #is_pio ); \ > > } while (0) > > > > Although the above codes is actually called, the addr might be freed > if `port >= PIO_RESERVED` is true. The double free still existed.
Of course. There exists a path in which the double free occurs. However, if you directly add this NULL assignment, it will cause a memory leak in other paths.
I am not suspecting the validation of this patch in defending the double free. Instead, I agree with this patch, but it may introduce some other issues, like memory leak.
> > > > If I make any mistakes, please tell me. > Thanks your report. > --- > Lv Yunlong > > > >
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