[PATCH] libdwfl: Fix some GCC10 -Wnull-dereference issues.

[Mark Wielaard]

GCC10 on some arches will warn about possible NULL derefences.
In the libdwfl linux-kernel-modules.c cases it might be caught already
by earlier calls to get_release (). But it is hard to see that will
really always happen. So do an explicit NULL check just in case.

Signed-off-by: Mark Wielaard <m...@klomp.org>
---
 libdwfl/ChangeLog              |  6 ++++++
 libdwfl/linux-kernel-modules.c | 13 ++++++++++---
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index b36a7ca6..0b95490a 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,3 +1,9 @@
+2020-01-24  Mark Wielaard  <m...@klomp.org>
+
+       * linux-kernel-modules.c (find_kernel_elf): Check release isn't NULL.
+       (report_kernel): Check release and *release aren't NULL.
+       (report_kernel_archive): Likewise.
+
 2019-12-11  Omar Sandoval  <osan...@fb.com>
 
        * libdwflP.h (Dwfl_Module): Remove coalescing state.
diff --git a/libdwfl/linux-kernel-modules.c b/libdwfl/linux-kernel-modules.c
index 48fb1ff0..0434f1e5 100644
--- a/libdwfl/linux-kernel-modules.c
+++ b/libdwfl/linux-kernel-modules.c
@@ -176,9 +176,10 @@ find_kernel_elf (Dwfl *dwfl, const char *release, char 
**fname)
 {
   /* First try to find an uncompressed vmlinux image.  Possibly
      including debuginfo.  */
-  if ((release[0] == '/'
-       ? asprintf (fname, "%s/vmlinux", release)
-       : asprintf (fname, "/boot/vmlinux-%s", release)) < 0)
+  if (release == NULL
+      || ((release[0] == '/'
+          ? asprintf (fname, "%s/vmlinux", release)
+          : asprintf (fname, "/boot/vmlinux-%s", release)) < 0))
     return -1;
 
   int fd = try_kernel_name (dwfl, fname, true);
@@ -241,6 +242,9 @@ report_kernel (Dwfl *dwfl, const char **release,
   if (unlikely (result != 0))
     return result;
 
+  if (release == NULL || *release == NULL)
+    return EINVAL;
+
   char *fname;
   int fd = find_kernel_elf (dwfl, *release, &fname);
 
@@ -296,6 +300,9 @@ report_kernel_archive (Dwfl *dwfl, const char **release,
   if (unlikely (result != 0))
     return result;
 
+  if (release == NULL || *release == NULL)
+    return EINVAL;
+
   char *archive;
   int res = (((*release)[0] == '/')
             ? asprintf (&archive, "%s/debug.a", *release)
-- 
2.18.1