Messages in this thread |  | | Date | Tue, 14 Jul 2020 11:32:56 +0200 | From | Thierry Reding <> | Subject | Re: [PATCH 2/2] usb: tegra: Fix zero length memory allocation |
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On Sun, Jul 12, 2020 at 11:28:37AM +0100, Jon Hunter wrote: > After commit cad064f1bd52 ("devres: handle zero size in devm_kmalloc()") > was added system suspend started failing on Tegra186. The kernel log > showed that the Tegra XHCI driver was crashing on entry to suspend when > attemptin the save the USB context. The problem is caused because we > are trying to allocate a zero length array for the IPFS context on > Tegra186 and following commit cad064f1bd52 ("devres: handle zero size > in devm_kmalloc()") this now causes a NULL pointer deference crash > when we try to access the memory. Fix this by only allocating memory > for both the IPFS and FPCI contexts when required. > > Cc: stable@vger.kernel.org > > Fixes: 5c4e8d3781bc ("usb: host: xhci-tegra: Add support for XUSB context save/restore") > > Signed-off-by: Jon Hunter <jonathanh@nvidia.com> > --- > drivers/usb/host/xhci-tegra.c | 22 ++++++++++++++-------- > 1 file changed, 14 insertions(+), 8 deletions(-)
Actually it would seem to me that this is no longer a bug after your fix in patch 1. We only ever access tegra->context.ipfs if tegra->soc->ipfs.num_offsets > 0, so the special ZERO_SIZE_PTR case will not actually cause an issue anymore.
The reason why this was crashing was because tegra->context.fpci was allocated with a zero size (because of the bug that you fixed in patch 1) and then that zero-size pointer was dereferenced because the code was correctly checking for tegra->soc->fpci.num_offsets > 0 in the context save and restore.
So I don't think there's a bug here. It's not wrong to allocate a zero- size buffer. It's only a bug to then go and dereference it. Are you still seeing the issue if you leave out this patch and only apply patch 1?
Thierry [unhandled content-type:application/pgp-signature] |  |