[Qemu-devel] [V10 PATCH 13/13] virtio-9p: Chroot environment for other functions

[M. Mohan Kumar]

Add chroot functionality for systemcalls that can operate on a file
using relative directory file descriptor.

Signed-off-by: M. Mohan Kumar <address@hidden>
---
 hw/9pfs/virtio-9p-local.c |  125 +++++++++++++++++++++++++++++++++++++++++----
 1 files changed, 115 insertions(+), 10 deletions(-)

diff --git a/hw/9pfs/virtio-9p-local.c b/hw/9pfs/virtio-9p-local.c
index def0c62..fa5c88f 100644
--- a/hw/9pfs/virtio-9p-local.c
+++ b/hw/9pfs/virtio-9p-local.c
@@ -22,6 +22,8 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <attr/xattr.h>
+#include <libgen.h>
+#include "qemu-error.h"
 
 /* Helper routine to fill V9fsFileObjectRequest structure */
 static int fill_fileobjectrequest(V9fsFileObjectRequest *request,
@@ -80,14 +82,42 @@ static int passthrough_request(FsContext *fs_ctx, const 
char *old_path,
     return retval;
 }
 
+/*
+ * Returns file descriptor of dirname(path)
+ * This fd can be used by *at functions
+ */
+static int get_dirfd(FsContext *fs_ctx, const char *path)
+{
+    int fd;
+    char *dpath;
+    char *last_component;
+
+    /* path can not contain ".." */
+    last_component = strrchr(path, '/');
+    if (last_component && !strcmp(last_component, "/..")) {
+        error_report("9p path request contains \"..\": %s\n", path);
+        errno = EFAULT;
+        return -1;
+    }
+    dpath = qemu_strdup(path);
+    fd = passthrough_request(fs_ctx, NULL, dirname(dpath), 0, NULL, T_OPEN);
+    qemu_free(dpath);
+    if (fd < 0) {
+        errno = -fd;
+        fd = -1;
+    }
+    return fd;
+}
+
 static int local_lstat(FsContext *fs_ctx, const char *path, struct stat *stbuf)
 {
     int err;
-    err =  lstat(rpath(fs_ctx, path), stbuf);
-    if (err) {
-        return err;
-    }
+
     if (fs_ctx->fs_sm == SM_MAPPED) {
+        err =  lstat(rpath(fs_ctx, path), stbuf);
+        if (err) {
+            return err;
+        }
         /* Actual credentials are part of extended attrs */
         uid_t tmp_uid;
         gid_t tmp_gid;
@@ -109,6 +139,26 @@ static int local_lstat(FsContext *fs_ctx, const char 
*path, struct stat *stbuf)
                         sizeof(dev_t)) > 0) {
                 stbuf->st_rdev = tmp_dev;
         }
+    } else if (fs_ctx->fs_sm == SM_PASSTHROUGH) {
+        int pfd, serrno = 0;
+        char *tmp_path;
+
+        pfd = get_dirfd(fs_ctx, path);
+        if (pfd < 0) {
+            return -1;
+        }
+        tmp_path = qemu_strdup(path);
+        err = fstatat(pfd, basename(tmp_path), stbuf, AT_SYMLINK_NOFOLLOW);
+        if (err < 0) {
+            serrno = errno;
+        }
+        close(pfd);
+        qemu_free(tmp_path);
+        if (err < 0) {
+            errno = serrno;
+        }
+    } else {
+        err =  lstat(rpath(fs_ctx, path), stbuf);
     }
     return err;
 }
@@ -173,9 +223,26 @@ static ssize_t local_readlink(FsContext *fs_ctx, const 
char *path,
         } while (tsize == -1 && errno == EINTR);
         close(fd);
         return tsize;
-    } else if ((fs_ctx->fs_sm == SM_PASSTHROUGH) ||
-               (fs_ctx->fs_sm == SM_NONE)) {
+    } else if (fs_ctx->fs_sm == SM_NONE) {
         tsize = readlink(rpath(fs_ctx, path), buf, bufsz);
+    } else if (fs_ctx->fs_sm == SM_PASSTHROUGH) {
+        int pfd, serrno = 0;
+        char *tmp_path;
+        pfd = get_dirfd(fs_ctx, path);
+        if (pfd < 0) {
+            return -1;
+        }
+
+        tmp_path = qemu_strdup(path);
+        tsize = readlinkat(pfd, basename(tmp_path), buf, bufsz);
+        if (tsize < 0) {
+            serrno = errno;
+        }
+        close(pfd);
+        qemu_free(tmp_path);
+        if (tsize < 0) {
+            errno = serrno;
+        }
     }
     return tsize;
 }
@@ -501,7 +568,25 @@ static int local_link(FsContext *fs_ctx, const char 
*oldpath,
 
 static int local_truncate(FsContext *ctx, const char *path, off_t size)
 {
-    return truncate(rpath(ctx, path), size);
+    if (ctx->fs_sm == SM_PASSTHROUGH) {
+        int fd, retval, serrno;
+        fd = passthrough_request(ctx, NULL, path, O_RDWR, NULL, T_OPEN);
+        if (fd < 0) {
+            errno = -fd;
+            return -1;
+        }
+        retval = ftruncate(fd, size);
+        if (retval < 0) {
+            serrno = errno;
+        }
+        close(fd);
+        if (retval < 0) {
+            errno = serrno;
+        }
+        return retval;
+    } else {
+        return truncate(rpath(ctx, path), size);
+    }
 }
 
 static int local_rename(FsContext *ctx, const char *oldpath,
@@ -541,10 +626,30 @@ static int local_chown(FsContext *fs_ctx, const char 
*path, FsCred *credp)
     return -1;
 }
 
-static int local_utimensat(FsContext *s, const char *path,
-                           const struct timespec *buf)
+static int local_utimensat(FsContext *fs_ctx, const char *path,
+                const struct timespec *buf)
 {
-    return qemu_utimensat(AT_FDCWD, rpath(s, path), buf, AT_SYMLINK_NOFOLLOW);
+    if (fs_ctx->fs_sm == SM_PASSTHROUGH) {
+        int fd, retval, serrno = 0;
+        fd = passthrough_request(fs_ctx, NULL, path,
+                        O_RDONLY | O_NONBLOCK | O_NOFOLLOW, NULL, T_OPEN);
+        if (fd < 0) {
+            errno = -fd;
+            return -1;
+        }
+        retval = futimens(fd, buf);
+        if (retval < 0) {
+            serrno = errno;
+        }
+        close(fd);
+        if (retval < 0) {
+            errno = serrno;
+        }
+        return retval;
+    } else {
+        return utimensat(AT_FDCWD, rpath(fs_ctx, path), buf,
+                        AT_SYMLINK_NOFOLLOW);
+    }
 }
 
 static int local_remove(FsContext *ctx, const char *path)
-- 
1.7.4