ANDROID: fix overflow in /proc/uid_cputime/remove_uid_range

Writing large values to remove_uid_range can cause an overflow &
system hang. To prevent this, read in the start and end of the range
using kstrtouint to ensure the full range can fit in a uid_t, and use
a u64 for our loop counters to avoid overflow when the range ends at
UINT_MAX.

Test: "echo '9223372036854775807-9223372036854775807'  > \
/proc/uid_cputime/remove_uid_range" now returns error instead of hanging
Bug: 139902843
Signed-off-by: Connor O'Brien <connoro@google.com>
Change-Id: I30138f95a1c56366a79eec27bbc476c9ea5773ae
2 files changed