sched/psi: Fix OOB write when writing 0 bytes to PSI files

BugLink: https://bugs.launchpad.net/bugs/1866165
commit 6fcca0fa48118e6d63733eb4644c6cd880c15b8f upstream.

Issuing write() with count parameter set to 0 on any file under
/proc/pressure/ will cause an OOB write because of the access to
buf[buf_size-1] when NUL-termination is performed. Fix this by checking
for buf_size to be non-zero.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Link: https://lkml.kernel.org/r/20200203212216.7076-1-surenb@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index ce8f6748678a24b51e390fc9210b776579fa4b7a..9154e745f09789dd3432af35d7db91f96068d1fe 100644 (file)
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -1199,6 +1199,9 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf,
        if (static_branch_likely(&psi_disabled))
                return -EOPNOTSUPP;
 
+       if (!nbytes)
+               return -EINVAL;
+
        buf_size = min(nbytes, sizeof(buf));
        if (copy_from_user(buf, user_buf, buf_size))
                return -EFAULT;