[git commit master] ash: refresh stack pointers after makestrspace in rmescapes

[Denys Vlasenko]

commit: http://git.busybox.net/busybox/commit/?id=3963d943f8a9b4ef89f000b5e1424e63dba920f5
branch: http://git.busybox.net/busybox/commit/?id=refs/heads/master

Without this, rmescapes sometimes returns random garbage while
performing parameter expansions such as ${foo#bar}, in the event that
the allocation of r happens to need to reallocate the stack and hence
invalidate str and p.  I'd love to provide a test case but unfortunately
it's dependent on exact stack layout, so I don't have anything simpler
than the situation described in
https://bugs.launchpad.net/ubuntu/+source/partman-base/+bug/527401/comments/23
which involved a sequence of foo="${foo#*, }" expansions on a long
string inside our RAID configuration tool.

The same fix has been in dash since 2007-09-26, contributed by Roy
Marples <uberlord at gentoo.org>.  I actually came up with it independently
almost to the character, but then synced it up with the variable naming
used in dash when I noticed that change afterwards.

Signed-off-by: Colin Watson <cjwatson at ubuntu.com>
Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 shell/ash.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/shell/ash.c b/shell/ash.c
index 9d55f89..ec5e0b8 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -5425,7 +5425,11 @@ rmescapes(char *str, int flag)
 		size_t fulllen = len + strlen(p) + 1;
 
 		if (flag & RMESCAPE_GROW) {
+			int strloc = str - (char *)stackblock();
 			r = makestrspace(fulllen, expdest);
+			/* p and str may be invalidated by makestrspace */
+			str = (char *)stackblock() + strloc;
+			p = str + len;
 		} else if (flag & RMESCAPE_HEAP) {
 			r = ckmalloc(fulllen);
 		} else {
-- 
1.6.3.3