[PATCH 0/1] MR4414: server: Fully initialize pe mapping struct to avoid uninitialized memory when...

[Fabian Maurer (＠DarkShadow44)]

When running wineserver under valgrind there is a bunch of uninitialised bytes warnings when sending the req_get_mapping_info reply.
This warning can easily be reproduced by running `valgrind wineserver -f` and then `winecfg`.
Tested using self compiled wine.

Reason is the `pe_image_info_t` struct having bitfields:
```
unsigned char  contains_code : 1;
unsigned char  wine_builtin : 1;
unsigned char  wine_fakedll : 1;
```
The last 5 bits are never initialized. This MR fixes this by zeroing the entire struct before it is filled.

I hope "issues" like this are allowed to be fixed so valgrind has less false positives.

Valgrind message for reference:
```
==628662== 716 errors in context 3 of 3:
==628662== Syscall param writev(vector[1]) points to uninitialised byte(s)
==628662==    at 0x49C3A87: writev (writev.c:26)
==628662==    by 0x14C2F3: send_reply (request.c:268)
==628662==    by 0x14C50F: call_req_handler (request.c:316)
==628662==    by 0x14C5D2: read_request (request.c:339)
==628662==    by 0x158F52: thread_poll_event (thread.c:388)
==628662==    by 0x120FC9: fd_poll_event (fd.c:505)
==628662==    by 0x1212A6: main_loop_epoll (fd.c:599)
==628662==    by 0x121882: main_loop (fd.c:955)
==628662==    by 0x12CBE0: main (main.c:238)
==628662==  Address 0x53ec56e is 62 bytes inside a block of size 88 alloc'd
==628662==    at 0x48416D4: malloc (vg_replace_malloc.c:431)
==628662==    by 0x1348D0: mem_alloc (object.c:119)
==628662==    by 0x14BEB9: set_reply_data_size (request.c:160)
==628662==    by 0x1301C1: req_get_mapping_info (mapping.c:1291)
==628662==    by 0x14C494: call_req_handler (request.c:305)
==628662==    by 0x14C5D2: read_request (request.c:339)
==628662==    by 0x158F52: thread_poll_event (thread.c:388)
==628662==    by 0x120FC9: fd_poll_event (fd.c:505)
==628662==    by 0x1212A6: main_loop_epoll (fd.c:599)
==628662==    by 0x121882: main_loop (fd.c:955)
==628662==    by 0x12CBE0: main (main.c:238)
==628662==  Uninitialised value was created by a client request
==628662==    at 0x134873: mark_block_uninitialized (object.c:110)
==628662==    by 0x1348EA: mem_alloc (object.c:120)
==628662==    by 0x134B87: alloc_object (object.c:199)
==628662==    by 0x134F92: create_named_object (object.c:337)
==628662==    by 0x12F12B: create_mapping (mapping.c:939)
==628662==    by 0x12FFE9: req_create_mapping (mapping.c:1250)
==628662==    by 0x14C494: call_req_handler (request.c:305)
==628662==    by 0x14C5D2: read_request (request.c:339)
==628662==    by 0x158F52: thread_poll_event (thread.c:388)
==628662==    by 0x120FC9: fd_poll_event (fd.c:505)
==628662==    by 0x1212A6: main_loop_epoll (fd.c:599)
==628662==    by 0x121882: main_loop (fd.c:955)
```

[PATCH 1/1] server: Fully initialize pe mapping struct to avoid uninitialized memory when sending req_get_mapping_info reply (valgrind)

[Fabian Maurer]

From: Fabian Maurer

---
 server/mapping.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/server/mapping.c b/server/mapping.c
index a795dc4b38b..dc790e99b59 100644
--- a/server/mapping.c
+++ b/server/mapping.c
@@ -977,7 +977,9 @@ static struct mapping *create_mapping( struct object *root, const struct unicode
         }
         if (flags & SEC_IMAGE)
         {
-            unsigned int err = get_image_params( mapping, st.st_size, unix_fd );
+            unsigned int err;
+            memset(&mapping->image, 0, sizeof(pe_image_info_t));
+            err = get_image_params( mapping, st.st_size, unix_fd );
             if (!err) return mapping;
             set_error( err );
             goto error;

[Fabian Maurer (＠DarkShadow44)]

Any news on this? Does this need improvement?

[Alexandre Julliard (＠julliard)]

There's no reason to clear the entire structure.

[Fabian Maurer (＠DarkShadow44)]

On Tue Nov 28 20:13:01 2023 +0000, Alexandre Julliard wrote:
> There's no reason to clear the entire structure.

Seemed the cleanest way to me. I mean, there's no way to take the address of a bitfield, so how else should I do it?