From: Stefan Hajnoczi <stefanha@redhat.com>

Date: Mon, 27 Jan 2020 19:01:22 +0000

Subject: [PATCH] virtiofsd: validate input buffer sizes in do_write_buf()

There is a small change in behavior: if fuse_write_in->size doesn't

match the input buffer size then the request is failed.  Previously

write requests with 1 fuse_buf element would truncate to

fuse_write_in->size.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Reviewed-by: Sergio Lopez <slp@redhat.com>

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

(cherry picked from commit 0ba8c3c6fce8fe949d59c1fd84d98d220ef9e759)

---

 tools/virtiofsd/fuse_lowlevel.c | 49 ++++++++++++++++++++-------------

 1 file changed, 30 insertions(+), 19 deletions(-)

diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c

index 7e10995adc..611e8b0354 100644

--- a/tools/virtiofsd/fuse_lowlevel.c

+++ b/tools/virtiofsd/fuse_lowlevel.c

@@ -1003,8 +1003,8 @@ static void do_write(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)

     }

 }

-static void do_write_buf(fuse_req_t req, fuse_ino_t nodeid, const void *inarg,

-                         struct fuse_bufvec *ibufv)

+static void do_write_buf(fuse_req_t req, fuse_ino_t nodeid,

+                         struct fuse_mbuf_iter *iter, struct fuse_bufvec *ibufv)

 {

     struct fuse_session *se = req->se;

     struct fuse_bufvec *pbufv = ibufv;

@@ -1012,28 +1012,27 @@ static void do_write_buf(fuse_req_t req, fuse_ino_t nodeid, const void *inarg,

         .buf[0] = ibufv->buf[0],

         .count = 1,

     };

-    struct fuse_write_in *arg = (struct fuse_write_in *)inarg;

+    struct fuse_write_in *arg;

+    size_t arg_size = sizeof(*arg);

     struct fuse_file_info fi;

     memset(&fi, 0, sizeof(fi));

+

+    arg = fuse_mbuf_iter_advance(iter, arg_size);

+    if (!arg) {

+        fuse_reply_err(req, EINVAL);

+        return;

+    }

+

+    fi.lock_owner = arg->lock_owner;

+    fi.flags = arg->flags;

     fi.fh = arg->fh;

     fi.writepage = arg->write_flags & FUSE_WRITE_CACHE;

     if (ibufv->count == 1) {

-        fi.lock_owner = arg->lock_owner;

-        fi.flags = arg->flags;

-        if (!(tmpbufv.buf[0].flags & FUSE_BUF_IS_FD)) {

-            tmpbufv.buf[0].mem = PARAM(arg);

-        }

-        tmpbufv.buf[0].size -=

-            sizeof(struct fuse_in_header) + sizeof(struct fuse_write_in);

-        if (tmpbufv.buf[0].size < arg->size) {

-            fuse_log(FUSE_LOG_ERR,

-                     "fuse: do_write_buf: buffer size too small\n");

-            fuse_reply_err(req, EIO);

-            return;

-        }

-        tmpbufv.buf[0].size = arg->size;

+        assert(!(tmpbufv.buf[0].flags & FUSE_BUF_IS_FD));

+        tmpbufv.buf[0].mem = ((char *)arg) + arg_size;

+        tmpbufv.buf[0].size -= sizeof(struct fuse_in_header) + arg_size;

         pbufv = &tmpbufv;

     } else {

         /*

@@ -1043,6 +1042,13 @@ static void do_write_buf(fuse_req_t req, fuse_ino_t nodeid, const void *inarg,

         ibufv->buf[0].size = 0;

     }

+    if (fuse_buf_size(pbufv) != arg->size) {

+        fuse_log(FUSE_LOG_ERR,

+                 "fuse: do_write_buf: buffer size doesn't match arg->size\n");

+        fuse_reply_err(req, EIO);

+        return;

+    }

+

     se->op.write_buf(req, nodeid, pbufv, arg->offset, &fi);

 }

@@ -2052,12 +2058,17 @@ void fuse_session_process_buf_int(struct fuse_session *se,

                                   struct fuse_chan *ch)

 {

     const struct fuse_buf *buf = bufv->buf;

+    struct fuse_mbuf_iter iter = FUSE_MBUF_ITER_INIT(buf);

     struct fuse_in_header *in;

     const void *inarg;

     struct fuse_req *req;

     int err;

-    in = buf->mem;

+    /* The first buffer must be a memory buffer */

+    assert(!(buf->flags & FUSE_BUF_IS_FD));

+

+    in = fuse_mbuf_iter_advance(&iter, sizeof(*in));

+    assert(in); /* caller guarantees the input buffer is large enough */

     if (se->debug) {

         fuse_log(FUSE_LOG_DEBUG,

@@ -2129,7 +2140,7 @@ void fuse_session_process_buf_int(struct fuse_session *se,

     inarg = (void *)&in[1];

     if (in->opcode == FUSE_WRITE && se->op.write_buf) {

-        do_write_buf(req, in->nodeid, inarg, bufv);

+        do_write_buf(req, in->nodeid, &iter, bufv);

     } else {

         fuse_ll_ops[in->opcode].func(req, in->nodeid, inarg);

     }