Libguestfs - Jan 2016 - [PATCH] inspect: resolve symlinks when detecting architecture

All the files in /bin are links to busybox.  guestfs_file_architecture
doesn't follow symlinks so it fails.  Therefore check /bin/busybox
(not a symlink) to find the architecture.
---
 src/inspect-fs-unix.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/inspect-fs-unix.c b/src/inspect-fs-unix.c
index f915e86..6aaf5a1 100644
--- a/src/inspect-fs-unix.c
+++ b/src/inspect-fs-unix.c
@@ -1077,7 +1077,8 @@ static void
 check_architecture (guestfs_h *g, struct inspect_fs *fs)
 {
   const char *binaries[] -    { "/bin/bash", "/bin/ls",
"/bin/echo", "/bin/rm", "/bin/sh" };
+    { "/bin/bash", "/bin/ls", "/bin/echo",
"/bin/rm", "/bin/sh",
+      "/bin/busybox" };
   size_t i;
   char *arch;
 
-- 
2.5.0

On Tuesday 26 January 2016 15:54:46 Richard W.M. Jones
wrote:
> All the files in /bin are links to busybox.  guestfs_file_architecture
> doesn't follow symlinks so it fails.  Therefore check /bin/busybox
> (not a symlink) to find the architecture.
> ---
While this patch looks okay in principle, I think it would be better
to just resolve the paths we are looking for: that is, do symlink
resolution in is_file, and use realpath to get the actual path before
passing it to file_architecture. If the file can be stat()ed, then it
is a relative symlink whose target we can read.

Patch coming in a minute.

-- 
Pino Toscano

Resolve the paths of the binaries we are looking in the guest to
identify the architecture. This way we can identify also busybox-based
guests such as Alpine Linux, where all the "base" binaries in /bin are
symlinks to busybox.
---
 src/inspect-fs-unix.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/src/inspect-fs-unix.c b/src/inspect-fs-unix.c
index f915e86..75c76f8 100644
--- a/src/inspect-fs-unix.c
+++ b/src/inspect-fs-unix.c
@@ -1082,10 +1082,22 @@ check_architecture (guestfs_h *g, struct inspect_fs *fs)
   char *arch;
 
   for (i = 0; i < sizeof binaries / sizeof binaries[0]; ++i) {
-    if (guestfs_is_file (g, binaries[i]) > 0) {
-      /* Ignore errors from file_architecture call. */
+    /* Allow symlinks when checking the binaries:,so in case they are
+     * relative ones (which can be resolved within the same partition),
+     * then we can check the architecture of their target.
+     */
+    if (guestfs_is_file_opts (g, binaries[i],
+                              GUESTFS_IS_FILE_OPTS_FOLLOWSYMLINKS, 1, -1) >
0) {
+      CLEANUP_FREE char *resolved = NULL;
+
+      /* Ignore errors from realpath and file_architecture calls. */
       guestfs_push_error_handler (g, NULL, NULL);
-      arch = guestfs_file_architecture (g, binaries[i]);
+      resolved = guestfs_realpath (g, binaries[i]);
+      /* If is_file above succeeded realpath should too, but better
+       * be safe than sorry.
+       */
+      if (resolved)
+        arch = guestfs_file_architecture (g, resolved);
       guestfs_pop_error_handler (g);
 
       if (arch) {
-- 
2.5.0