[Qemu-devel] [PATCH v4 7/7] osdep: Enable qemu_open to dup pre-opened fd

[Corey Bryant <coreyb@linux.vnet.ibm.com>]

This patch adds support to qemu_open to dup(fd) a pre-opened file
descriptor if the filename is of the format /dev/fd/X.

This can be used when QEMU is restricted from opening files, and
the management application opens files on QEMU's behalf.

If the fd was passed to the monitor with the pass-fd command, it
must be explicitly closed with the 'closefd' command when it is
no longer required, in order to prevent fd leaks.

Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com>
---
v2:
 -Get rid of file_open and move dup code to qemu_open
  (kwolf@redhat.com)
 -Use strtol wrapper instead of atoi (kwolf@redhat.com)

v3:
 -Add note about fd leakage (eblake@redhat.com)

v4
 -Moved patch to be later in series (lcapitulino@redhat.com)
 -Update qemu_open to check access mode flags and set flags that
  can be set (eblake@redhat.com, kwolf@redhat.com)

 cutils.c      |   26 +++++++++++++----
 main-loop.c   |    6 ++--
 osdep.c       |   91 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 qemu-common.h |    2 +-
 4 files changed, 116 insertions(+), 9 deletions(-)

diff --git a/cutils.c b/cutils.c
index af308cd..f45d921 100644
--- a/cutils.c
+++ b/cutils.c
@@ -339,17 +339,33 @@ bool buffer_is_zero(const void *buf, size_t len)
 }
 
 #ifndef _WIN32
-/* Sets a specific flag */
-int fcntl_setfl(int fd, int flag)
+/* Sets a specific flag on or off */
+int fcntl_setfl(int fd, int flag, int onoff)
 {
     int flags;
 
+    if (onoff != 0 && onoff != 1) {
+        return -EINVAL;
+    }
+
     flags = fcntl(fd, F_GETFL);
-    if (flags == -1)
+    if (flags == -1) {
         return -errno;
+    }
 
-    if (fcntl(fd, F_SETFL, flags | flag) == -1)
-        return -errno;
+    if (onoff == 1) {
+        if ((flags & flag) != flag) {
+            if (fcntl(fd, F_SETFL, flags | flag) == -1) {
+                return -errno;
+            }
+        }
+    } else {
+        if ((flags & flag) == flag) {
+            if (fcntl(fd, F_SETFL, flags & ~flag) == -1) {
+                return -errno;
+            }
+        }
+    }
 
     return 0;
 }
diff --git a/main-loop.c b/main-loop.c
index eb3b6e6..644fcc3 100644
--- a/main-loop.c
+++ b/main-loop.c
@@ -75,11 +75,11 @@ static int qemu_event_init(void)
     if (err == -1) {
         return -errno;
     }
-    err = fcntl_setfl(fds[0], O_NONBLOCK);
+    err = fcntl_setfl(fds[0], O_NONBLOCK, 1);
     if (err < 0) {
         goto fail;
     }
-    err = fcntl_setfl(fds[1], O_NONBLOCK);
+    err = fcntl_setfl(fds[1], O_NONBLOCK, 1);
     if (err < 0) {
         goto fail;
     }
@@ -154,7 +154,7 @@ static int qemu_signal_init(void)
         return -errno;
     }
 
-    fcntl_setfl(sigfd, O_NONBLOCK);
+    fcntl_setfl(sigfd, O_NONBLOCK, 1);
 
     qemu_set_fd_handler2(sigfd, NULL, sigfd_handler, NULL,
                          (void *)(intptr_t)sigfd);
diff --git a/osdep.c b/osdep.c
index 3e6bada..a6fc758d 100644
--- a/osdep.c
+++ b/osdep.c
@@ -73,6 +73,63 @@ int qemu_madvise(void *addr, size_t len, int advice)
 #endif
 }
 
+/*
+ * Dups an fd and sets the flags
+ */
+static int qemu_dup(int fd, int flags)
+{
+    int ret;
+    int serrno;
+
+    if (flags & O_CLOEXEC) {
+        ret = fcntl(fd, F_DUPFD_CLOEXEC, 0);
+        if (ret == -1 && errno == EINVAL) {
+            ret = dup(fd);
+            if (ret == -1) {
+                goto fail;
+            }
+            if (fcntl_setfl(ret, O_CLOEXEC, (flags & O_CLOEXEC) ? 1 : 0) < 0) {
+                goto fail;
+            }
+        }
+    } else {
+        ret = dup(fd);
+    }
+
+    if (ret == -1) {
+        goto fail;
+    }
+
+    /* Truncate the file in the cases that open would truncate it */
+    if (flags & O_TRUNC ||
+            ((flags & (O_CREAT | O_EXCL)) == (O_CREAT | O_EXCL))) {
+        if (ftruncate(ret, 0) == -1) {
+            goto fail;
+        }
+    }
+
+    if ((fcntl_setfl(ret, O_APPEND,    (flags & O_APPEND)    ? 1 : 0) < 0) ||
+        (fcntl_setfl(ret, O_ASYNC,     (flags & O_ASYNC)     ? 1 : 0) < 0) ||
+        (fcntl_setfl(ret, O_DIRECT,    (flags & O_DIRECT)    ? 1 : 0) < 0) ||
+        (fcntl_setfl(ret, O_LARGEFILE, (flags & O_LARGEFILE) ? 1 : 0) < 0) ||
+        (fcntl_setfl(ret, O_NDELAY,    (flags & O_NDELAY)    ? 1 : 0) < 0) ||
+        (fcntl_setfl(ret, O_NOATIME,   (flags & O_NOATIME)   ? 1 : 0) < 0) ||
+        (fcntl_setfl(ret, O_NOCTTY,    (flags & O_NOCTTY)    ? 1 : 0) < 0) ||
+        (fcntl_setfl(ret, O_NONBLOCK,  (flags & O_NONBLOCK)  ? 1 : 0) < 0) ||
+        (fcntl_setfl(ret, O_SYNC,      (flags & O_SYNC)      ? 1 : 0) < 0)) {
+        goto fail;
+    }
+
+    return ret;
+
+fail:
+    serrno = errno;
+    if (ret != -1) {
+        close(ret);
+    }
+    errno = serrno;
+    return -1;
+}
 
 /*
  * Opens a file with FD_CLOEXEC set
@@ -82,6 +139,40 @@ int qemu_open(const char *name, int flags, ...)
     int ret;
     int mode = 0;
 
+#ifndef _WIN32
+    const char *p;
+
+    /* Attempt dup of fd for pre-opened file */
+    if (strstart(name, "/dev/fd/", &p)) {
+        int fd;
+        int eflags;
+
+        fd = qemu_parse_fd(p);
+        if (fd == -1) {
+            return -1;
+        }
+
+        /* Get the existing fd's flags */
+        eflags = fcntl(fd, F_GETFL);
+        if (eflags == -1) {
+            return -1;
+        }
+
+        if (((flags & O_RDWR) != (eflags & O_RDWR)) ||
+            ((flags & O_RDONLY) != (eflags & O_RDONLY)) ||
+            ((flags & O_WRONLY) != (eflags & O_WRONLY))) {
+            errno = EACCES;
+            return -1;
+        }
+
+        if (fcntl_setfl(fd, O_CLOEXEC, 1) < 0) {
+            return -1;
+        }
+
+        return qemu_dup(fd, flags);
+    }
+#endif
+
     if (flags & O_CREAT) {
         va_list ap;
 
diff --git a/qemu-common.h b/qemu-common.h
index 91e0562..99cbbc5 100644
--- a/qemu-common.h
+++ b/qemu-common.h
@@ -144,7 +144,7 @@ int qemu_strnlen(const char *s, int max_len);
 time_t mktimegm(struct tm *tm);
 int qemu_fls(int i);
 int qemu_fdatasync(int fd);
-int fcntl_setfl(int fd, int flag);
+int fcntl_setfl(int fd, int flag, int onoff);
 int qemu_parse_fd(const char *param);
 
 /*
-- 
1.7.10.2