virtiofsd: Save error code early at the failure callsite

Git-commit: 1e08f164e9fdc9528ad6990012301b9a04b0bc90
References: bsc#1183373, CVE-2021-20263

Change error code handling slightly in lo_setattr(). Right now we seem
to jump to out_err and assume that "errno" is valid and use that to
send reply.

But if caller has to do some other operations before jumping to out_err,
then it does the dance of first saving errno to saverr and the restore
errno before jumping to out_err. This makes it more confusing.

I am about to make more changes where caller will have to do some
work after error before jumping to out_err. I found it easier to
change the convention a bit. That is caller saves error in "saverr"
before jumping to out_err. And out_err uses "saverr" to send error
back and does not rely on "errno" having actual error.

v3: Resolved conflicts in lo_setattr() due to lo_inode_open() changes.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20210208224024.43555-2-vgoyal@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Bruce Rogers <brogers@suse.com>

diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index 90f5281..200a1d2 100644 (file)
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -710,6 +710,7 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
             res = fchmodat(lo->proc_self_fd, procname, attr->st_mode, 0);
         }
         if (res == -1) {
+            saverr = errno;
             goto out_err;
         }
     }
@@ -719,6 +720,7 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
 
         res = fchownat(ifd, "", uid, gid, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
         if (res == -1) {
+            saverr = errno;
             goto out_err;
         }
     }
@@ -730,16 +732,15 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
         } else {
             truncfd = lo_inode_open(lo, inode, O_RDWR);
             if (truncfd < 0) {
-                errno = -truncfd;
+                saverr = -truncfd;
                 goto out_err;
             }
         }
 
         res = ftruncate(truncfd, attr->st_size);
+        saverr = res == -1 ? errno : 0;
         if (!fi) {
-            saverr = errno;
             close(truncfd);
-            errno = saverr;
         }
         if (res == -1) {
             goto out_err;
@@ -772,6 +773,7 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
             res = utimensat(lo->proc_self_fd, procname, tv, 0);
         }
         if (res == -1) {
+            saverr = errno;
             goto out_err;
         }
     }
@@ -780,7 +782,6 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
     return lo_getattr(req, ino, fi);
 
 out_err:
-    saverr = errno;
     lo_inode_put(lo, &inode);
     fuse_reply_err(req, saverr);
 }