commit ba584f1de30e58b0d93cd81bd437271b894eefbf
author Andreas Schwab <schwab@suse.de> Tue Mar 05 17:45:05 2019 +0100
committer Laurent Vivier <laurent@vivier.eu> Thu Mar 07 10:57:29 2019 +0100
tree 0acddcc77db3ff6d4ded9942616c5a3969003f07
parent 14c8a3a157b437e54fbe097d991dca86ac828a14

linux-user: don't short-circuit read with zero length

A zero-length read still needs to do the usual checks, thus it may return
errors like EBADF.  This makes the read syscall emulation consistent with
the pread64 syscall emulation.

Signed-off-by: Andreas Schwab <schwab@suse.de>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <mvm5zsxz2we.fsf@suse.de>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

linux-user/syscall.c

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 5f72209..9f7eb7d 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -7009,8 +7009,8 @@
         _exit(arg1);
         return 0; /* avoid warning */
     case TARGET_NR_read:
-        if (arg3 == 0) {
-            return 0;
+        if (arg2 == 0 && arg3 == 0) {
+            return get_errno(safe_read(arg1, 0, 0));
         } else {
             if (!(p = lock_user(VERIFY_WRITE, arg2, arg3, 0)))
                 return -TARGET_EFAULT;