klibc - Mar 2020 - [klibc:update-dash] dash: expand: Fix multiple issues with EXP_DISCARD in evalvar

Commit-ID:  1285f79afbd9686c78c7815203ecbf3e87a81ff8
Gitweb:    
http://git.kernel.org/?p=libs/klibc/klibc.git;a=commit;h=1285f79afbd9686c78c7815203ecbf3e87a81ff8
Author:     Herbert Xu <herbert at gondor.apana.org.au>
AuthorDate: Wed, 12 Sep 2018 14:27:16 +0800
Committer:  Ben Hutchings <ben at decadent.org.uk>
CommitDate: Sat, 28 Mar 2020 21:42:55 +0000

[klibc] dash: expand: Fix multiple issues with EXP_DISCARD in evalvar

[ dash commit a29e9a1738a4e7040211842f3f3d90e172fa58ce ]

The commit 3cd538634f71538370f5af239f342aec48b7470b broke parameter
expansion in multiple ways because the EXP_DISCARD flag wasn't set
or tested for various cases:

	$ src/dash -c 'var=; echo ${var:+nonempty}'
	nonempty
        $ src/dash -u -c 'unset foo bar; echo ${foo+${bar}}'
        dash: 1: bar: parameter not set
        $ src/dash -c 'foo=bar; echo ${foo=BUG}; echo $foo'
        barBUG
        bar
        $

This patch fixes them by introducing a new discard variable that
tracks whether the extra word should be discarded or not when it
is parsed.

Reported-by: Martijn Dekker <martijn at inlv.org>
Fixes: 3cd538634f71 ("expand: Do not reprocess data when...")
Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
Reported-by: Martijn Dekker <martijn at inlv.org>
Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
Signed-off-by: Ben Hutchings <ben at decadent.org.uk>

---
 usr/dash/expand.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/usr/dash/expand.c b/usr/dash/expand.c
index 411381bd..25236c09 100644
--- a/usr/dash/expand.c
+++ b/usr/dash/expand.c
@@ -698,6 +698,7 @@ evalvar(char *p, int flag)
 	int patloc;
 	int startloc;
 	ssize_t varlen;
+	int discard;
 	int quoted;
 
 	varflags = *p++;
@@ -713,41 +714,41 @@ again:
 	if (varflags & VSNUL)
 		varlen--;
 
+	discard = varlen < 0 ? EXP_DISCARD : 0;
+
 	switch (subtype) {
 	case VSPLUS:
-		varlen = -1 - varlen;
+		discard ^= EXP_DISCARD;
 		/* fall through */
 
 	case 0:
 	case VSMINUS:
-		p = argstr(p, flag | EXP_TILDE | EXP_WORD);
-		if (varlen < 0)
-			return p;
+		p = argstr(p, flag | EXP_TILDE | EXP_WORD |
+			      (discard ^ EXP_DISCARD));
 		goto record;
 
 	case VSASSIGN:
 	case VSQUESTION:
-		if (varlen >= 0)
-			goto record;
-
 		p = subevalvar(p, var, 0, startloc, varflags,
-			       flag & ~QUOTES_ESC);
+			       (flag & ~QUOTES_ESC) |
+			       (discard ^ EXP_DISCARD));
 
-		if (flag & EXP_DISCARD)
-			return p;
+		if ((flag | ~discard) & EXP_DISCARD)
+			goto record;
 
 		varflags &= ~VSNUL;
+		subtype = VSNORMAL;
 		goto again;
 	}
 
-	if (varlen < 0 && uflag)
+	if ((discard & ~flag) && uflag)
 		varunset(p, var, 0, 0);
 
 	if (subtype == VSLENGTH) {
 		if (flag & EXP_DISCARD)
 			return p;
 		cvtnum(varlen > 0 ? varlen : 0, flag);
-		goto record;
+		goto really_record;
 	}
 
 	if (subtype == VSNORMAL)
@@ -765,7 +766,7 @@ again:
 	}
 #endif
 
-	flag |= varlen < 0 ? EXP_DISCARD : 0;
+	flag |= discard;
 	if (!(flag & EXP_DISCARD)) {
 		/*
 		 * Terminate the string and start recording the pattern
@@ -778,9 +779,10 @@ again:
 	p = subevalvar(p, NULL, patloc, startloc, varflags, flag);
 
 record:
-	if (flag & EXP_DISCARD)
+	if ((flag | discard) & EXP_DISCARD)
 		return p;
 
+really_record:
 	if (quoted) {
 		quoted = *var == '@' && shellparam.nparam;
 		if (!quoted)