[Qemu-devel] [PATCH v2 1/1] Handle /proc/self/exe in syscall execve

[Olivier Dion <olivier.dion@polymtl.ca>]

If not handled, QEMU will execve itself instead of the emulated
process.  The function do_openat already solves the /proc/self/exe
problem, so we can use it to get the executable file descriptor.  We
then make a safe call to execveat.

Note that safe_execve has been replaced by safe_execveat, since the
former is now useless.

Signed-off-by: Olivier Dion <olivier.dion@polymtl.ca>
---
 linux-user/syscall.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index e2af3c1494..68340bcb67 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -736,7 +736,7 @@ safe_syscall4(pid_t, wait4, pid_t, pid, int *, status, int, options, \
               struct rusage *, rusage)
 safe_syscall5(int, waitid, idtype_t, idtype, id_t, id, siginfo_t *, infop, \
               int, options, struct rusage *, rusage)
-safe_syscall3(int, execve, const char *, filename, char **, argv, char **, envp)
+safe_syscall5(int, execveat, int, dirfd, const char *, pathname, char **, argv, char **, envp, int, flags)
 safe_syscall6(int, pselect6, int, nfds, fd_set *, readfds, fd_set *, writefds, \
               fd_set *, exceptfds, struct timespec *, timeout, void *, sig)
 safe_syscall5(int, ppoll, struct pollfd *, ufds, unsigned int, nfds,
@@ -7507,8 +7507,18 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
              * before the execve completes and makes it the other
              * program's problem.
              */
-            ret = get_errno(safe_execve(p, argp, envp));
-            unlock_user(p, arg1, 0);
+            {
+                int execfd = get_errno(do_openat(cpu_env, AT_FDCWD, p, O_PATH, 0));
+                unlock_user(p, arg1, 0);
+                if (is_error(execfd)) {
+                    ret = execfd;
+                    goto execve_end;
+                }
+                ret = get_errno(safe_execveat(execfd, "",
+                                              argp, envp,
+                                              AT_EMPTY_PATH));
+                close(execfd);
+            }
 
             goto execve_end;
 
-- 
2.23.0