ash: expand: Fix multiple issues with EXP_DISCARD in evalvar

Upstream commit:

    Date: Wed, 12 Sep 2018 14:27:16 +0800
    expand: Fix multiple issues with EXP_DISCARD in evalvar

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

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 14 insertions, 14 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 425da6bb6..d0d99f60e 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -7454,6 +7454,7 @@ evalvar(char *p, int flag)
         int patloc;
         int startloc;
         ssize_t varlen;
+        int discard;
         int quoted;
 
         varflags = (unsigned char) *p++;
@@ -7469,33 +7470,31 @@ evalvar(char *p, int flag)
         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) {
@@ -7503,7 +7502,7 @@ evalvar(char *p, int flag)
                 if (flag & EXP_DISCARD)
                         return p;
                 cvtnum(varlen > 0 ? varlen : 0, flag);
-                goto record;
+                goto really_record;
         }
 
         if (subtype == VSNORMAL)
@@ -7528,7 +7527,7 @@ evalvar(char *p, int flag)
         }
 #endif
 
-        flag |= varlen < 0 ? EXP_DISCARD : 0;
+        flag |= discard;
         if (!(flag & EXP_DISCARD)) {
                 /*
                  * Terminate the string and start recording the pattern
@@ -7541,9 +7540,10 @@ evalvar(char *p, int flag)
         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)