rshim logging buffer could overflow and get lost

[Liming Sun]

On Bluefield platforms, the 'bfrshlog' script can be used to write a string into the internal rshim logging buffer which has size 1KB. When the buffer is full, the intention is to drop the new data. However, due to a bug, the buffer could be overwritten and wrap-around when full.

SRU Justification:

[Impact]
* When 'cat /dev/rshim0/misc' with DISPLAY_LEVEL set to 2, the logging buffer could be potentially displayed as empty when it's full.

[Fix]
* Add the check properly to make sure the buffer won't wrap-around.

[Test Case]
* Run "bfrshlog <some-message>" repeatedly and check the /dev/rshim0/misc with DISPLAY_LEVEL set to 2 in this file. The buffer shouldn't be overwritten or wrap-around.

[Regression Potential]
* The rshim log can be displayed by setting "DISPLAY_LEVEL 2" in /dev/rshim0/misc, then "cat /dev/rshim0/misc" to see the log messages. The log should contains ATF/UEFI booting progress and user logs from Linux applications by using the bfrshlog script. In any case, the log should always start from ATF logging, not overwritten or wrap-around. When the buffer is full, new data will be dropped.

[Other]
* N/A

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-focal' to 'verification-done-focal'. If the problem still exists, change the tag 'verification-needed-focal' to 'verification-failed-focal'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

[Liming Sun (lsun)]

Verified that the same fix has been available in the master-next branch.

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux-bluefield - 5.4.0-1011.14

---------------
linux-bluefield (5.4.0-1011.14) focal; urgency=medium

  * focal/linux-bluefield: 5.4.0-1011.14 -proposed tracker (LP: #1923761)

  * kernel crash with stress CT offload traffic (LP: #1922672)
    - netfilter: conntrack: Move nf_ct_offload_timeout to header file
    - netfilter: flowtable: Set offload timeout when adding flow

  * support offloading of ct_state flags invalid and reply (LP: #1922682)
    - net/sched: cls_flower add CT_FLAGS_INVALID flag support
    - net/sched: act_api: fix miss set post_ct for ovs after do conntrack in
      act_ct
    - net/sched: act_ct: clear post_ct if doing ct_clear
    - net/sched: cls_flower: Add match on the ct_state reply flag
    - net: flow_offload: Add original direction flag to ct_metadata

  * netfilter offload could bloat up memory (LP: #1922678)
    - netfilter: flowtable: separate replace, destroy and stats to different
      workqueues
    - SAUCE: netfilter: nf_flow_table_offload: Limit work entries on offload add
      wq

  * TLS fixes (LP: #1916508)
    - net/tls: Add asynchronous resync
    - net/tls: fix sign extension issue when left shifting u16 value
    - net/tls: Fix wrong record sn in async mode of device resync

  * ipmb_host.c: Fix slow transactions (LP: #1922393)
    - SAUCE: ipmb_host.c: Fix slow transactions

  * i2c-mlx.c: sync up with upstream (LP: #1921506)
    - SAUCE: Syncup i2c-mlx driver with upstreamed version

  [ Ubuntu: 5.4.0-73.82 ]

  * focal/linux: 5.4.0-73.82 -proposed tracker (LP: #1923781)
  * Packaging resync (LP: #1786013)
    - update dkms package versions
  * CIFS DFS entries not accessible with 5.4.0-71.74-generic (LP: #1923670)
    - Revert "cifs: Set CIFS_MOUNT_USE_PREFIX_PATH flag on setting
      cifs_sb->prepath."
  * CVE-2021-29650
    - Revert "netfilter: x_tables: Update remaining dereference to RCU"
    - Revert "netfilter: x_tables: Switch synchronization to RCU"
    - netfilter: x_tables: Use correct memory barriers.
  * LRMv4: switch to signing nvidia modules via the Ubuntu Modules signing key
    (LP: #1918134)
    - [Packaging] dkms-build{,--nvidia-N} sync back from LRMv4
  * 5.4 kernel: when iommu is on crashdump fails (LP: #1922738)
    - iommu/vt-d: Refactor find_domain() helper
    - iommu/vt-d: Add attach_deferred() helper
    - iommu/vt-d: Move deferred device attachment into helper function
    - iommu/vt-d: Do deferred attachment in iommu_need_mapping()
    - iommu/vt-d: Remove deferred_attach_domain()
    - iommu/vt-d: Simplify check in identity_mapping()
  * Backport mlx5e fix for tunnel offload (LP: #1921769)
    - net/mlx5e: Check tunnel offload is required before setting SWP
  * Bcache bypasse writeback on caching device with fragmentation (LP: #1900438)
    - bcache: consider the fragmentation when update the writeback rate
  * Fix implicit declaration warnings for kselftests/memfd test on newer
    releases (LP: #1910323)
    - selftests/memfd: Fix implicit declaration warnings
  * net/mlx5e: Add missing capability check for uplink follow (LP: #1921104)
    - net/mlx5e: Add missing capability check for uplink follow
  * [UBUNUT 21.04] s390/vti...