** Changed in: linux (Ubuntu)
Status: In Progress => Fix Released
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https://bugs.launchpad.net/bugs/1874444
Title:
Bionic ubuntu ethtool doesn't check ring parameters boundaries
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Xenial:
Fix Released
Status in linux source package in Bionic:
Fix Released
Bug description:
[Impact]
* There's a bad behavior in the ena driver ringparam setting on kernels 4.4
and 4.15, if an invalid ringparam is provided to ethtool.
* Upstream Linux kernel implemented ring parameter boundaries check in
commit: 37e2d99b59c4 ("ethtool: Ensure new ring parameters are within bounds
during SRINGPARAM") [ git.kernel.org/linus/37e2d99b59c4 ].
Due to this commit, the community doesn't usually allow ring parameter
boundary checks in driver code.
* Xenial/Bionic kernels don't include this patch, and some network
drivers (like ena) rely on this patch for boundary checking of ring
params. So, we are hereby requesting the commit inclusion in these
kernel versions.
[Test case]
1. In AWS, create a new c5.4xlarge instance with the Ubuntu 18.04 official
ami (uses the ENA network driver) and update to latest kernel/reboot.
2. Run ethtool -g ens5
output:
Ring parameters for ens5:
Pre-set maximums:
RX: 16384
RX Mini: 0
RX Jumbo: 0
TX: 1024
Current hardware settings:
RX: 1024
RX Mini: 0
RX Jumbo: 0
TX: 1024
3. Change the TX/RX ring size to a legal number within boundaries -
works!
4. Change the TX/RX ring size to an illegal number (such as 2048 for
TX) with the command - "sudo ethtool -G ens5 tx 2048".
Expected behavior - "Cannot set device ring parameters: Invalid argument"
Actual behavior - causes a driver hang since boundaries are not checked by
ethtool, effectively hanging the instance (given that AWS has no console to
allow system manipulation).
[Regression Potential]
Since that the commit is present in kernels v4.16+ (including Ubuntu)
and is quite small and self-contained, the regression risk is very
reduced.
One potential "regression" would be if some driver has bugs and
provide bad values on get_ringparams, then the validation would be
broken (allowing illegal values or refusing legal ones), but this
wouldn't be a regression in the hereby proposed patch itself, it'd be
only exposed by the patch.
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