[Qemu-devel] [PATCH] hostmem-file: fix pmem file size check

[Qemu-devel] [PATCH] hostmem-file: fix pmem file size check

[Stefan Hajnoczi]

Commit 314aec4a6e06844937f1677f6cba21981005f389 ("hostmem-file: reject
invalid pmem file sizes") added a file size check that verifies the
hostmem object's size parameter against the actual devdax pmem file.
This is useful because getting the size wrong results in confusing
errors inside the guest.

However, the code doesn't work properly for files where struct
stat::st_size is zero.  Hostmem-file's ->alloc() function returns early
without setting an Error, causing the following assertion failure:

  qemu/memory.c:2215: memory_region_get_ram_ptr: Assertion `mr->ram_block' failed.

This patch handles the case where qemu_get_pmem_size() returns 0 but
there is no error.

Fixes: 314aec4a6e06844937f1677f6cba21981005f389
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 backends/hostmem-file.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index 29e55c9195..ecc15e3eb0 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -67,12 +67,12 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
         uint64_t size;
 
         size = qemu_get_pmem_size(fb->mem_path, &local_err);
-        if (!size) {
+        if (local_err) {
             error_propagate(errp, local_err);
             return;
         }
 
-        if (backend->size > size) {
+        if (size && backend->size > size) {
             error_setg(errp, "size property %" PRIu64 " is larger than "
                        "pmem file \"%s\" size %" PRIu64, backend->size,
                        fb->mem_path, size);
-- 
2.21.0

Re: [Qemu-devel] [PATCH] hostmem-file: fix pmem file size check

[Eduardo Habkost]

On Fri, Aug 23, 2019 at 02:56:32PM +0100, Stefan Hajnoczi wrote:
> Commit 314aec4a6e06844937f1677f6cba21981005f389 ("hostmem-file: reject
> invalid pmem file sizes") added a file size check that verifies the
> hostmem object's size parameter against the actual devdax pmem file.
> This is useful because getting the size wrong results in confusing
> errors inside the guest.
> 
> However, the code doesn't work properly for files where struct
> stat::st_size is zero.  Hostmem-file's ->alloc() function returns early
> without setting an Error, causing the following assertion failure:
> 
>   qemu/memory.c:2215: memory_region_get_ram_ptr: Assertion `mr->ram_block' failed.
> 
> This patch handles the case where qemu_get_pmem_size() returns 0 but
> there is no error.
> 
> Fixes: 314aec4a6e06844937f1677f6cba21981005f389
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Queued, thanks.

-- 
Eduardo