From: Jean-Christian CÎRSTEA <jean.christian.cirstea@gmail.com>

Since Linux 6.11, the path argument may be NULL.

Before this patch, qemu-*-linux-user failed with EFAULT when `pathname` was
specified as NULL, even for Linux kernel hosts > 6.10. This patch fixes this
issue by checking whether `arg2` is 0. If so, don't return EFAULT, but instead
perform the appropiate syscall and let the host's kernel handle null `pathname`.

Cc: qemu-stable@nongnu.org
Signed-off-by: Jean-Christian CÎRSTEA <jean.christian.cirstea@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20251229121416.2209295-1-jean.christian.cirstea@gmail.com>
(cherry picked from commit 82ae60c8b5cb98d610056a1e2d0ba72e9ef7907c)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index dcca90cfee..77bdbf20ae 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -11908,9 +11908,13 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1,
             int dirfd = arg1;
             int flags = arg3;
 
-            p = lock_user_string(arg2);
-            if (p == NULL) {
-                return -TARGET_EFAULT;
+            p = NULL;
+            /* Since Linux 6.11, the path argument may be NULL */
+            if (arg2 != 0) {
+                p = lock_user_string(arg2);
+                if (p == NULL) {
+                    return -TARGET_EFAULT;
+                }
             }
 #if defined(__NR_statx)
             {
-- 
2.47.3