ash: don't read past end of var in subvareval for bash substitutions

Without this patch, BusyBox handles bash pattern substitutions without
a terminating '/' character incorrectly.

Consider the following shell script:

	_bootstrapver=5.0.211-r0
	_referencesdir="/usr/${_bootstrapver/-*}/Sources"
	echo $_referencesdir

This should output `/usr/5.0.211/Sources`. However, without this patch
it instead outputs `/usr/5.0.211Sources`. This is due to the fact that
BusyBox expects the bash pattern substitutions to always be terminated
with a '/' (at least in this part of subvareval) and thus reads passed
the substitution itself and consumes the '/' character which is part of
the literal string. If there is no '/' after the substitution then
BusyBox might perform an out-of-bounds read under certain circumstances.

When replacing the bash pattern substitution with `${_bootstrapver/-*/}`,
or with this patch applied, ash outputs the correct value.

Signed-off-by: Sören Tempel <soeren@soeren-tempel.net>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

5 files changed, 10 insertions, 0 deletions

diff --git a/shell/ash.c b/shell/ash.c
index adb0f223a..54335c5dd 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -7081,6 +7081,10 @@ subevalvar(char *start, char *str, int strloc,
                                 *repl = '\0';
                                 break;
                         }
+                        if ((unsigned char)*repl == CTLENDVAR) { /* ${v/pattern} (no trailing /, no repl) */
+                                repl = NULL;
+                                break;
+                        }
                         /* Handle escaped slashes, e.g. "${v/\//_}" (they are CTLESC'ed by this point) */
                         if ((unsigned char)*repl == CTLESC && repl[1])
                                 repl++;
diff --git a/shell/ash_test/ash-vars/var_bash_repl_unterminated.right b/shell/ash_test/ash-vars/var_bash_repl_unterminated.right
new file mode 100644
index 000000000..5bff3a6fa
--- /dev/null
+++ b/shell/ash_test/ash-vars/var_bash_repl_unterminated.right
@@ -0,0 +1 @@
+b/d
diff --git a/shell/ash_test/ash-vars/var_bash_repl_unterminated.tests b/shell/ash_test/ash-vars/var_bash_repl_unterminated.tests
new file mode 100755
index 000000000..c9513343d
--- /dev/null
+++ b/shell/ash_test/ash-vars/var_bash_repl_unterminated.tests
@@ -0,0 +1,2 @@
+a=b-c
+echo ${a/-*}/d
diff --git a/shell/hush_test/hush-vars/var_bash_repl_unterminated.right b/shell/hush_test/hush-vars/var_bash_repl_unterminated.right
new file mode 100644
index 000000000..5bff3a6fa
--- /dev/null
+++ b/shell/hush_test/hush-vars/var_bash_repl_unterminated.right
@@ -0,0 +1 @@
+b/d
diff --git a/shell/hush_test/hush-vars/var_bash_repl_unterminated.tests b/shell/hush_test/hush-vars/var_bash_repl_unterminated.tests
new file mode 100755
index 000000000..c9513343d
--- /dev/null
+++ b/shell/hush_test/hush-vars/var_bash_repl_unterminated.tests
@@ -0,0 +1,2 @@
+a=b-c
+echo ${a/-*}/d