Re: [PATCH] lxc: fix lxcContainerMountAllFS() DEREF_BEFORE_CHECK
On Wed, Sep 06, 2023 at 18:34:42 +0300, Dmitry Frolov wrote:
Reviewing the sources, I found, that
in function lxcContainerMountAllFS() pointers
vmDef->fss[i]->src and vmDef->fss[i]->src->path
are checked for NULL after dereferencing in
VIR_DEBUG() macro.
Fixes: 57487085dc ("lxc: don't try to reference NULL when mounting
filesystems")
---
src/lxc/lxc_container.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index 21220661f7..58a6695458 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -1467,13 +1467,15 @@ static int lxcContainerMountAllFS(virDomainDef *vmDef,
if (STREQ(vmDef->fss[i]->dst, "/"))
continue;
+ if (!(vmDef->fss[i]->src && vmDef->fss[i]->src->path))
+ return -1;
This would return -1 without reporting any error. And you are also
changing the logic here without explaining it. If vmDef->fss[i]->src was
NULL or vmDef->fss[i]->src->path was NULL this function would call
lxcContainerUnmountSubtree on vmDef->fss[i]->dst before, but now it just
returns -1. Well except that it would crash first :-) In any case, this
part is wrong, see below...
+
VIR_DEBUG("Mounting '%s' -> '%s'",
vmDef->fss[i]->src->path, vmDef->fss[i]->dst);
if (lxcContainerResolveSymlinks(vmDef->fss[i], false) < 0)
return -1;
- if (!(vmDef->fss[i]->src && vmDef->fss[i]->src->path
&&
- STRPREFIX(vmDef->fss[i]->src->path, vmDef->fss[i]->dst))
&&
+ if (!STRPREFIX(vmDef->fss[i]->src->path, vmDef->fss[i]->dst)
&&
lxcContainerUnmountSubtree(vmDef->fss[i]->dst, false) < 0)
return -1;
I checked our parsing code and vmDef->fss[i]->src can never be NULL as
it is always allocated in virDomainFSDefNew so checking it is redundant.
On the other hand vmDef->fss[i]->src->path can be NULL, but it is not en
error, e.g., VIR_DOMAIN_FS_TYPE_RAM would contain path == NULL.
So the fix should rather remove the check for vmDef->fss[i]->src and use
NULLSTR(vmDef->fss[i]->src->path) in VIR_DEBUG.
Jirka