[PATCH] net/9p: Validate current->sighand in client.c

[Alexander Kapshuk]

Use (un)lock_task_sighand instead of spin_lock_irqsave and
spin_unlock_irqrestore to ensure current->sighand is a valid pointer as
suggested in the email referenced below.

Signed-off-by: Alexander Kapshuk <alexander.kaps...@gmail.com>
Link: https://lore.kernel.org/lkml/20200618190807.GA20699@nautica/
---
 net/9p/client.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/net/9p/client.c b/net/9p/client.c
index fc1f3635e5dd..15f16f2baa8f 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -787,9 +787,14 @@ p9_client_rpc(struct p9_client *c, int8_t type, const char 
*fmt, ...)
        }
 recalc_sigpending:
        if (sigpending) {
-               spin_lock_irqsave(&current->sighand->siglock, flags);
+               if (!lock_task_sighand(current, &flags)) {
+                       pr_warn("%s (%d): current->sighand==NULL in 
recalc_sigpending\n",
+                               __func__, task_pid_nr(current));
+                       err = -ESRCH;
+                       goto reterr;
+               }
                recalc_sigpending();
-               spin_unlock_irqrestore(&current->sighand->siglock, flags);
+               unlock_task_sighand(current, &flags);
        }
        if (err < 0)
                goto reterr;
@@ -869,9 +874,14 @@ static struct p9_req_t *p9_client_zc_rpc(struct p9_client 
*c, int8_t type,
        }
 recalc_sigpending:
        if (sigpending) {
-               spin_lock_irqsave(&current->sighand->siglock, flags);
+               if (!lock_task_sighand(current, &flags)) {
+                       pr_warn("%s (%d): current->sighand==NULL in 
recalc_sigpending\n",
+                               __func__, task_pid_nr(current));
+                       err = -ESRCH;
+                       goto reterr;
+               }
                recalc_sigpending();
-               spin_unlock_irqrestore(&current->sighand->siglock, flags);
+               unlock_task_sighand(current, &flags);
        }
        if (err < 0)
                goto reterr;
--
2.27.0