[PULL 4/8] linux-user: rt_sigprocmask, check read perms first

[Laurent Vivier]

From: Shu-Chun Weng <scw@google.com>

Linux kernel does it this way (checks read permission before validating `how`)
and the latest version of ABSL's `AddressIsReadable()` depends on this
behavior.

c.f.  
https://github.com/torvalds/linux/blob/9539ba4308ad5bdca6cb41c7b73cbb9f796dcdd7/kernel/signal.c#L3147
Reviewed-by: Patrick Venture <venture@google.com>
Signed-off-by: Shu-Chun Weng <scw@google.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Patrick Venture <venture@google.com>
Message-Id: <20220126212559.1936290-2-venture@google.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
---
 linux-user/syscall.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 2ca0f086dbfc..9f8b497fa353 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -9478,6 +9478,13 @@ static abi_long do_syscall1(void *cpu_env, int num, 
abi_long arg1,
             }
 
             if (arg2) {
+                p = lock_user(VERIFY_READ, arg2, sizeof(target_sigset_t), 1);
+                if (!p) {
+                    return -TARGET_EFAULT;
+                }
+                target_to_host_sigset(&set, p);
+                unlock_user(p, arg2, 0);
+                set_ptr = &set;
                 switch(how) {
                 case TARGET_SIG_BLOCK:
                     how = SIG_BLOCK;
@@ -9491,11 +9498,6 @@ static abi_long do_syscall1(void *cpu_env, int num, 
abi_long arg1,
                 default:
                     return -TARGET_EINVAL;
                 }
-                if (!(p = lock_user(VERIFY_READ, arg2, 
sizeof(target_sigset_t), 1)))
-                    return -TARGET_EFAULT;
-                target_to_host_sigset(&set, p);
-                unlock_user(p, arg2, 0);
-                set_ptr = &set;
             } else {
                 how = 0;
                 set_ptr = NULL;
-- 
2.34.1