Libguestfs - Apr 2023 - [rhel-9.2 v2v PATCH 2/2] detect_kernels: deal with RHEL's kernel-core / kernel-modules-core split

In "kernel-5.14.0-269.el9", the "kernel-modules-core"
subpackage got split
from the "kernel-core" subpackage. Therefore, a single binary RPM
containing *both* the "/boot/vmlinuz-5.14.0-269.el9.x86_64" file *and*
the
"/lib/modules/5.14.0-269.el9.x86_64" directory no longer exists. The
file
now belongs to "kernel-core", and the directory to
"kernel-modules-core".

As a result, when we investigate the file list of "kernel-core" (based
on
"kernel-core" providing
"/boot/vmlinuz-5.14.0-269.el9.x86_64"), the first
match against "/lib/modules/" is not the actual module root directory
"/lib/modules/5.14.0-269.el9.x86_64", but the nonsensical
"/lib/modules/5.14.0-269.el9.x86_64/.vmlinuz.hmac" regular file. This
latter file is never a directory, therefore we rule out "kernel-core"
as a
kernel package.

We also rule out "kernel-modules-core" (even earlier) because it does
not
contain "/boot/vmlinuz-5.14.0-269.el9.x86_64".

Now, the code already deals with the case if the prospective kernel
package *does not provide a match* for the "/lib/modules/" prefix: in
that
case, we construct the modpath manually, from said prefix, and the version
number found in "/boot/vmlinuz-<version>". This fallback is
good, but it's
unreachable if *there is* a candidate, it's just wrong (i.e., not a
directory).

Perform the "is_dir" check on the candidate modpath earlier, so that
we
can fall back to the manual modpath construction if the modpath candidate
exists, but is wrong.

With this, the original "is_dir" check becomes superfluous
(duplicated)
*except* when the "Not_found" branch is taken. Therefore, hoist the
original "is_dir" check into that branch.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2175703
Reported-by: Vera Wu <vwu at redhat.com>
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
Tested-by: Vera Wu <vwu at redhat.com>
(ported from libguestfs-common commit 70c10a079a30ff3a84f38596d725a6c5d46e2470)
---
 convert/linux_kernels.ml | 24 +++++++++++++++-----
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/convert/linux_kernels.ml b/convert/linux_kernels.ml
index 75ab94c45551..d0b316437072 100644
--- a/convert/linux_kernels.ml
+++ b/convert/linux_kernels.ml
@@ -124,7 +124,7 @@ let detect_kernels (g : G.guestfs) inspect family bootloader
let prefix = "/lib/modules/" in
              let prefix_len = String.length prefix in
              try
-               List.find_map (
+               let modpath, version = List.find_map (
                  fun filename ->
                    let filename_len = String.length filename in
                    if filename_len > prefix_len &&
@@ -134,17 +134,29 @@ let detect_kernels (g : G.guestfs) inspect family
bootloader                       Some (filename, version)
                    ) else
                      None
-               ) files
+               ) files in
+               (* Fall back to the version in the vmlinuz file name not only if
+                * a candidate pathname couldn't be found under
/lib/modules/,
+                * but also in case the candidate pathname doesn't reference
a
+                * directory. See RHBZ#2175703.
+                *
+                * Note that this "is_dir" check is deliberately kept
outside of
+                * the "find_map"'s mapper function above: we want
the first
+                * candidate *to be* a directory, and not the first candidate
+                * *that is* a directory.
+                *)
+               if not (g#is_dir ~followsymlinks:true modpath) then
+                 raise Not_found;
+               modpath, version
              with Not_found ->
                let version                   String.sub vmlinuz 14
(String.length vmlinuz - 14) in
                let modpath = prefix ^ version in
+               (* Check that the modpath exists. *)
+               if not (g#is_dir ~followsymlinks:true modpath) then
+                 raise Not_found;
                modpath, version in
 
-           (* Check that the modpath exists. *)
-           if not (g#is_dir ~followsymlinks:true modpath) then
-             raise Not_found;
-
            (* Find the initramfs which corresponds to the kernel.
             * Since the initramfs is built at runtime, and doesn't have
             * to be covered by the RPM file list, this is basically

For the series, since this is a straight backport of the upstream
patch with the filenames changed:

Reviewed-by: Richard W.M. Jones <rjones at redhat.com>
> https://bugzilla.redhat.com/show_bug.cgi?id=2175703
Looks like we're going to do this as a 0-day z-stream backport?
You are assignee so I'll leave it alone unless you need any help with it.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
nbdkit - Flexible, fast NBD server with plugins
https://gitlab.com/nbdkit/nbdkit