[Libguestfs] [PATCH libguestfs] daemon: rpm: Check return values from librpm calls

[Richard W.M. Jones]

We previously didn't bother to check the return values from any librpm
calls.  In some cases where possibly the RPM database is faulty, this
caused us to return a zero-length list of installed applications (but
no error indication).

One way to reproduce this is given below.  Note this reproducer will
only work when run on a RHEL 8 host (or more specifically, with
rpm <= 4.16):

$ virt-builder fedora-28
$ guestfish -a fedora-28.img -i rm /var/lib/rpm/Packages
$ guestfish --ro -a fedora-28.img -i inspect-list-applications /dev/sda4 -vx
...
chroot: /sysroot: running 'librpm'
error: cannot open Packages index using db5 - Read-only file system (30)
error: cannot open Packages database in
error: cannot open Packages index using db5 - Read-only file system (30)
error: cannot open Packages database in
librpm returned 0 installed packages
...

With this commit we get an error instead:

...
chroot: /sysroot: running 'librpm'
error: cannot open Packages index using db5 - Read-only file system (30)
error: cannot open Packages database in
ocaml_exn: 'internal_list_rpm_applications' raised 'Failure' exception
guestfsd: error: rpmtsInitIterator
guestfsd: => internal_list_rpm_applications (0x1fe) took 0.01 secs
libguestfs: trace: internal_list_rpm_applications = NULL (error)
libguestfs: error: internal_list_rpm_applications: rpmtsInitIterator
libguestfs: trace: inspect_list_applications2 = NULL (error)
libguestfs: trace: inspect_list_applications = NULL (error)
...

Not in this case, but in some cases of corrupt RPM databases it is
possible to recover them by running "rpmdb --rebuilddb" as a guest
command (ie. with guestfs_sh).

See-also: https://bugzilla.redhat.com/show_bug.cgi?id=2089623#c12
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2089623
Fixes: commit c9ee831affed55abe0f928134cbbd2ed83b2f510
Reported-by: Xiaodai Wang
Reported-by: Ming Xie
---
 daemon/rpm-c.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/daemon/rpm-c.c b/daemon/rpm-c.c
index 74d325a17b..2cb50a62d2 100644
--- a/daemon/rpm-c.c
+++ b/daemon/rpm-c.c
@@ -24,6 +24,7 @@
 #include <inttypes.h>
 #include <string.h>
 #include <unistd.h>
+#include <errno.h>
 
 #include <caml/alloc.h>
 #include <caml/fail.h>
@@ -79,7 +80,14 @@ value
 guestfs_int_daemon_rpm_init (value unitv)
 {
   CAMLparam1 (unitv);
-  rpmReadConfigFiles (NULL, NULL);
+
+  /* Nothing in actual RPM C code bothers to check if this call
+   * succeeds, so using that as an example, just print a debug message
+   * if it failed, but continue.  (The librpm Python bindings do check)
+   */
+  if (rpmReadConfigFiles (NULL, NULL) == -1)
+    fprintf (stderr, "rpmReadConfigFiles: failed, errno=%d\n", errno);
+
   CAMLreturn (Val_unit);
 }
 
@@ -92,6 +100,8 @@ guestfs_int_daemon_rpm_start_iterator (value unitv)
   CAMLparam1 (unitv);
 
   ts = rpmtsCreate ();
+  if (ts == NULL)
+    caml_failwith ("rpmtsCreate");
 
 #ifdef RPMVSF_MASK_NOSIGNATURES
   /* Disable signature checking (RHBZ#2064182). */
@@ -99,6 +109,14 @@ guestfs_int_daemon_rpm_start_iterator (value unitv)
 #endif
 
   iter = rpmtsInitIterator (ts, RPMDBI_PACKAGES, NULL, 0);
+  /* This could return NULL in theory if there are no packages, but
+   * that could not happen in a real guest.  However it also returns
+   * NULL when unable to open the database (RHBZ#2089623) which is
+   * something we do need to detect.
+   */
+  if (iter == NULL)
+    caml_failwith ("rpmtsInitIterator");
+
   CAMLreturn (Val_unit);
 }
 
-- 
2.35.1