kconfig: Avoid buffer underrun in choice input

commit 40aee729b350672c2550640622416a855e27938f ('kconfig: fix default
value for choice input') fixed some cases where kconfig would select
the wrong option from a choice with a single valid option and thus
enter an infinite loop.

However, this broke the test for user input of the form 'N?', because
when kconfig selects the single valid option the input is zero-length
and the test will read the byte before the input buffer.  If this
happens to contain '?' (as it will in a mips build on Debian unstable
today) then kconfig again enters an infinite loop.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: stable@kernel.org [2.6.17+]
Signed-off-by: Michal Marek <mmarek@suse.cz>

diff --git a/scripts/kconfig/conf.c b/scripts/kconfig/conf.c
index 659326c3e89579b09f86077dbcbe5e1eb3a12d28..006ad817cd5f003023a7308b471eb9c4e46ba5de 100644 (file)
--- a/scripts/kconfig/conf.c
+++ b/scripts/kconfig/conf.c
@@ -332,7 +332,7 @@ static int conf_choice(struct menu *menu)
                }
                if (!child)
                        continue;
-               if (line[strlen(line) - 1] == '?') {
+               if (line[0] && line[strlen(line) - 1] == '?') {
                        print_help(child);
                        continue;
                }