[X][B][C][D][Unstable][SRU][PATCH 0/1] sysctl: handle overflow in proc_get_long

[Po-Hsu Lin]

== SRU Justification ==
With the upper / lower boundary confined in bug 1834310, the file-max
is still suffering with overflow issue.

This is because the simple_strtoul() used in proc_get_long() to parse
user input explicitly ignores overflows. So when you tried to put 2^64
into file-max, it will:
    # echo 18446744073709551616 > /proc/sys/fs/file-max
    # cat /proc/sys/fs/file-max
    0

Which will cause your system to silently die behind your back.

This issue was reported by the case 1 of the sysctl02 test in LTP:
sysctl02 1 TFAIL: /proc/sys/fs/file-max overflows and set to 0


== Fix ==
* 7f2923c4 (sysctl: handle overflow in proc_get_long)

A new strtoul_lenient() was introduced here to solve this issue, with
extra check to notify userspace with -EINVAL.

This patch can be cherry-picked into B/C/D/E, it needs some content
adjustment for X.

== Test ==
Test kernels could be found here:
https://people.canonical.com/~phlin/kernel/lp-1833935-proc_get_long/

The attempt to set file-max to 2^64 will be rejected:
$ sudo sysctl -w -q fs.file-max=18446744073709551616
sysctl: setting key "fs.file-max": Invalid argument

Tested and passed with these kernels on AMD64 KVM nodes.

== Regression Potential ==
Low, the newly introduced function strtoul_lenient() is just for
proc_get_long here.

Christian Brauner (1):
  sysctl: handle overflow in proc_get_long

 kernel/sysctl.c | 40 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 39 insertions(+), 1 deletion(-)

-- 
2.7.4