hush: fix G.argv0_for_re_execing to avoid endless loop

When the busybox is used as /sbin/init and the inittab file contains
below:

::respawn:-/bin/sh

/sbin/init spawns hush for the first time with the argv[0] contains '-',
and hush treats it as login shell.  Then it reads /etc/profile and if
the file contains the command execution like below, it invokes hush as
login shell because the argv[0] argument is still '-/bin/sh' and reads
/etc/profile again.  This will last until some failure (e.g., memory
failure) happens.

  [ "$(id -u)" -eq 0 ] && PS1="${PS1}# " || PS1="${PS1}\$ "

This commit fixes this issues by adding an offset (+1) to the
G.argv0_for_re_execing variable.

This issue happens on our out-of-tree UML (use mode linux) with nommu
configuration.

Link: https://lore.kernel.org/all/cover.1731290567.git.thehajime@gmail.com/
Signed-off-by: Hajime Tazaki <thehajime@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/shell/hush.c b/shell/hush.c
index 04dda0734..4a97293cc 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -10361,6 +10361,9 @@ int hush_main(int argc, char **argv)
                 _exit(0);
         }
         G.argv0_for_re_execing = argv[0];
+        if (G.argv0_for_re_execing[0] == '-')
+                /* reexeced hush should never be a login shell */
+                G.argv0_for_re_execing++;
 #endif
 #if ENABLE_HUSH_TRAP
 # if ENABLE_HUSH_FUNCTIONS