sysctl: Disallow partial updates for erroneous sysctl vectors

When updating the kernel sysctl vectors there is a chance that not all
vector elements are updated due to erroneous input. Use a staging
variable that holds a copy of the vector and commits to the actual
table->data only when all input is successfully updated. This does
**not** make the write atomic as a reader can still see a partially
updated vector.

The staging is only for vectors; cases where table->data points to a
variable should not be staged as they will not be updated on input
error. PROC_VEC_UINT is not included because UINT arrays are not
allowed.

Replace first with nr_conv, incremented where first was cleared. first
is exactly nr_conv == 0, and the counter doubles as the number of
elements to publish.

Example of behavior that is being prevented:

  # 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 <- incorrect

It should be unchanged ("4 4 1 7") on error.

Link: https://lore.kernel.org/all/tencent_A860C873956A52E26AD8D309A308A241BA08@qq.com/
Reviewed-by: Bradley Morgan <include@grrlz.net>
Signed-off-by: Joel Granados <joel.granados@kernel.org>

0 files changed, 0 insertions, 0 deletions