diff options
| author | Eric Biggers <ebiggers@google.com> | 2017-11-07 14:15:27 -0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-11-30 08:39:01 +0000 |
| commit | 443d26a6f791506ca6fdab58b355ba7e170f741e (patch) | |
| tree | 5fe9bc3302caf779b464a4b7c5fceb65d90da8b5 | |
| parent | fb8bd56e35e18725e216b1aa2adcf8d9adc7f438 (diff) | |
lib/mpi: call cond_resched() from mpi_powm() loop
commit 1d9ddde12e3c9bab7f3d3484eb9446315e3571ca upstream.
On a non-preemptible kernel, if KEYCTL_DH_COMPUTE is called with the
largest permitted inputs (16384 bits), the kernel spends 10+ seconds
doing modular exponentiation in mpi_powm() without rescheduling. If all
threads do it, it locks up the system. Moreover, it can cause
rcu_sched-stall warnings.
Notwithstanding the insanity of doing this calculation in kernel mode
rather than in userspace, fix it by calling cond_resched() as each bit
from the exponent is processed. It's still noninterruptible, but at
least it's preemptible now.
Do the cond_resched() once per bit rather than once per MPI limb because
each limb might still easily take 100+ milliseconds on slow CPUs.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | lib/mpi/mpi-pow.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/lib/mpi/mpi-pow.c b/lib/mpi/mpi-pow.c index e24388a863a7..468fb7cd1221 100644 --- a/lib/mpi/mpi-pow.c +++ b/lib/mpi/mpi-pow.c @@ -26,6 +26,7 @@ * however I decided to publish this code under the plain GPL. */ +#include <linux/sched.h> #include <linux/string.h> #include "mpi-internal.h" #include "longlong.h" @@ -256,6 +257,7 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod) } e <<= 1; c--; + cond_resched(); } i--; |