busybox: ash/hush fix for read-builtin command

this is a cherrypick from busybox-git HEAD:
f5470419404d643070db99d058405b714695b817

and can be removed when upgrading to
next busybox release. discussion here:
http://lists.busybox.net/pipermail/busybox/2017-May/085439.html

Signed-off-by: Bastian Bittorf <[email protected]>

package/utils/busybox/501-ash-hush-fix-SIGCHLD-interrupting-read-builtin.patch

@@ -0,0 +1,147 @@
+From f5470419404d643070db99d058405b714695b817 Mon Sep 17 00:00:00 2001
+From: Denys Vlasenko <[email protected]>
+Date: Mon, 22 May 2017 19:34:45 +0200
+Subject: [PATCH] ash,hush: fix SIGCHLD interrupting read builtin
+
+function                                             old     new   delta
+readcmd                                              169     217     +48
+shell_builtin_read                                  1087    1097     +10
+localcmd                                             366     364      -2
+builtin_read                                         197     193      -4
+------------------------------------------------------------------------------
+(add/remove: 0/0 grow/shrink: 2/2 up/down: 58/-6)              Total: 52 bytes
+
+Signed-off-by: Denys Vlasenko <[email protected]>
+Signed-off-by: Bastian Bittorf <[email protected]>
+---
+ shell/ash.c                                  |  7 +++++++
+ shell/ash_test/ash-read/read_SIGCHLD.right   |  2 ++
+ shell/ash_test/ash-read/read_SIGCHLD.tests   |  4 ++++
+ shell/hush.c                                 |  5 ++++-
+ shell/hush_test/hush-read/read_SIGCHLD.right |  2 ++
+ shell/hush_test/hush-read/read_SIGCHLD.tests |  4 ++++
+ shell/shell_common.c                         | 20 +++++++++++---------
+ 7 files changed, 34 insertions(+), 10 deletions(-)
+ create mode 100644 shell/ash_test/ash-read/read_SIGCHLD.right
+ create mode 100755 shell/ash_test/ash-read/read_SIGCHLD.tests
+ create mode 100644 shell/hush_test/hush-read/read_SIGCHLD.right
+ create mode 100755 shell/hush_test/hush-read/read_SIGCHLD.tests
+
+diff --git a/shell/ash.c b/shell/ash.c
+index 70ee15e..60c8ffe 100644
+--- a/shell/ash.c
++++ b/shell/ash.c
+@@ -13268,6 +13268,7 @@ readcmd(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
+ 	/* "read -s" needs to save/restore termios, can't allow ^C
+ 	 * to jump out of it.
+ 	 */
++ again:
+ 	INT_OFF;
+ 	r = shell_builtin_read(setvar0,
+ 		argptr,
+@@ -13280,6 +13281,12 @@ readcmd(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
+ 	);
+ 	INT_ON;
+ 
++	if ((uintptr_t)r == 1 && errno == EINTR) {
++		/* to get SIGCHLD: sleep 1 & read x; echo $x */
++		if (pending_sig == 0)
++			goto again;
++	}
++
+ 	if ((uintptr_t)r > 1)
+ 		ash_msg_and_raise_error(r);
+ 
+diff --git a/shell/ash_test/ash-read/read_SIGCHLD.right b/shell/ash_test/ash-read/read_SIGCHLD.right
+new file mode 100644
+index 0000000..b3dc7ab
+--- /dev/null
++++ b/shell/ash_test/ash-read/read_SIGCHLD.right
+@@ -0,0 +1,2 @@
++x='Ok'
++exitcode:0
+diff --git a/shell/ash_test/ash-read/read_SIGCHLD.tests b/shell/ash_test/ash-read/read_SIGCHLD.tests
+new file mode 100755
+index 0000000..c5f673a
+--- /dev/null
++++ b/shell/ash_test/ash-read/read_SIGCHLD.tests
+@@ -0,0 +1,4 @@
++x=BAD
++{ sleep 0.4; echo Ok; } | { sleep 0.2 & read x; echo "x='$x'"; }
++echo "exitcode:$?"
++
+diff --git a/shell/hush.c b/shell/hush.c
+index e18920f..125463a 100644
+--- a/shell/hush.c
++++ b/shell/hush.c
+@@ -9038,6 +9038,9 @@ static int FAST_FUNC builtin_type(char **argv)
+  * - terminates shell (regardless of interactivity);
+  * if it has non-empty trap:
+  * - executes trap and returns to read;
++ * SIGCHLD from children:
++ * - does not interrupt read regardless of interactivity:
++ *   try: sleep 1 & read x; echo $x
+  */
+ static int FAST_FUNC builtin_read(char **argv)
+ {
+@@ -9071,7 +9074,7 @@ static int FAST_FUNC builtin_read(char **argv)
+ 
+ 	if ((uintptr_t)r == 1 && errno == EINTR) {
+ 		unsigned sig = check_and_run_traps();
+-		if (sig && sig != SIGINT)
++		if (sig != SIGINT)
+ 			goto again;
+ 	}
+ 
+diff --git a/shell/hush_test/hush-read/read_SIGCHLD.right b/shell/hush_test/hush-read/read_SIGCHLD.right
+new file mode 100644
+index 0000000..b3dc7ab
+--- /dev/null
++++ b/shell/hush_test/hush-read/read_SIGCHLD.right
+@@ -0,0 +1,2 @@
++x='Ok'
++exitcode:0
+diff --git a/shell/hush_test/hush-read/read_SIGCHLD.tests b/shell/hush_test/hush-read/read_SIGCHLD.tests
+new file mode 100755
+index 0000000..c5f673a
+--- /dev/null
++++ b/shell/hush_test/hush-read/read_SIGCHLD.tests
+@@ -0,0 +1,4 @@
++x=BAD
++{ sleep 0.4; echo Ok; } | { sleep 0.2 & read x; echo "x='$x'"; }
++echo "exitcode:$?"
++
+diff --git a/shell/shell_common.c b/shell/shell_common.c
+index fb86e68..03b7d0b 100644
+--- a/shell/shell_common.c
++++ b/shell/shell_common.c
+@@ -204,15 +204,17 @@ shell_builtin_read(void FAST_FUNC (*setvar)(const char *name, const char *val),
+ 		c = buffer[bufpos];
+ 		if (c == '\0')
+ 			continue;
+-		if (backslash) {
+-			backslash = 0;
+-			if (c != '\n')
+-				goto put;
+-			continue;
+-		}
+-		if (!(read_flags & BUILTIN_READ_RAW) && c == '\\') {
+-			backslash = 1;
+-			continue;
++		if (!(read_flags & BUILTIN_READ_RAW)) {
++			if (backslash) {
++				backslash = 0;
++				if (c != '\n')
++					goto put;
++				continue;
++			}
++			if (c == '\\') {
++				backslash = 1;
++				continue;
++			}
+ 		}
+ 		if (c == '\n')
+ 			break;
+-- 
+1.9.1
+