[PATCH v2 0/4] sysctl: Disallow partial updates of miss-formatted sysctl vectors

[Joel Granados <joel.granados@kernel.org>]

What?
=====

Stage table->data when writing INT & ULONG ctl_tables. Commit staged
data to kernel variable only when all the conversions have succeeded.
This is applicable only to variables that represent a vector; paths
pertaining to scalers are left unchanged. Notice that partial updates
can still happen if less than the size of the vector are passed and
correctly formatted.

This is the behavior we are protecting against:

  # echo "4 4 1 7" > /proc/sys/kernel/printk
  # echo "1 x" > /proc/sys/kernel/printk
  -bash: echo: write error: Invalid argument
  # cat /proc/sys/kernel/printk
  1 4 1 7    <- the write failed, the first element changed anyway

Why?
====
Allowing a partial change to a vector after returning from an erroneous
proc_handler is just plain wrong. This should be handled within sysctl
to avoid users having to do it for themselves [1]. 

Behavioral Changes
==================
1. A failed write will not update the vector
2. Vector writes can now fail with -ENOMEM

Testing
=======
This went through regular sysctl kunit and self test. Also is posted to
0-day.

I always find it difficult to know who wants to receive this. Please let
me know if you want to be removed from the Cc/To.

Best

[1] https://lore.kernel.org/all/tencent_A860C873956A52E26AD8D309A308A241BA08@qq.com/

Signed-off-by: Joel Granados <joel.granados@kernel.org>
---
Changes in v2:
- Avoid doc compilation warnings related to apply_conv_on_vec function
- Initialize rc in testing to avoid a false positive when executing 0013
  individually
- Link to v1: https://lore.kernel.org/r/20260813-lklm-partial_ctlvec-v1-0-df9e51c13704@kernel.org

---
Joel Granados (4):
      sysctl: Split data conversion and file position handling
      sysctl: Reject uint arrays before calling the general proc_vec
      sysctl: Disallow partial updates for erroneous sysctl vectors
      sysctl: Add 0013 to test partially updated vectors

 kernel/sysctl.c                          | 237 ++++++++++++++++++++-----------
 tools/testing/selftests/sysctl/sysctl.sh |  60 ++++++++
 2 files changed, 217 insertions(+), 80 deletions(-)
---
base-commit: 4c12287001da60f3c022bb25932aa7a5590fc0b1
change-id: 20260813-lklm-partial_ctlvec-bd8867b70d5c

Best regards,
-- 
Joel Granados <joel.granados@kernel.org>