Hi Guillaume and all involved, it seems this bug still can occur even
with the backported fix [0]. I found an upstream new fix that is quite
promising, it addresses this specific oops. In the past it was thought
by maintainers that other fix [0] could reduce the likelihood of those
crashes in smb2_push_mandatory_locks (and it may worked, reducing the
occurrence), but the fact is a proper fix was never worked until kernel
5.5.
The commit is 6f582b273ec2 ("CIFS: Fix NULL-pointer dereference in
smb2_push_mandatory_locks") [1]. The reasoning about the fix is that the
struct cifsFileInfo is initialized and ready for usage before all
members are initialized, like cifs->tlink (the one being dereferenced in
most oops reports). The maintainer then enforced full struct
initialization before it gets used.
I've built a 4.15 Bionic kernel with this fix, available in the following PPA:
launchpad.net/~gpiccoli/+archive/ubuntu/test1795659
To use this kernel, one just needs to run:
sudo add-apt-repository ppa:gpiccoli/test1795659
sudo apt-get update
sudo apt install linux-image-unsigned-4.15.0-74-generic
linux-modules-4.15.0-74-generic linux-modules-extra-4.15.0-74-generic
Then reboot the machine and check if the right kernel is running; to verify
that,
just run "uname -rv" and the output should be:
4.15.0-74-generic #84+TEST256303v20191229b1-Ubuntu <...>
In case anybody reproducing this issue can test the PPA kernel, I'd strongly
appreciate it.
Cheers,
Guilherme
[0] http://git.kernel.org/linus/b98749cac4a6
[1] http://git.kernel.org/linus/6f582b273ec2
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https://bugs.launchpad.net/bugs/1795659
Title:
kernel panic using CIFS share in smb2_push_mandatory_locks()
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