CVE-2016-6323: Backtraces can hang on ARM EABI (32-bit) (swbz#20435)

glibc-swbz20435.patch

@@ -0,0 +1,39 @@
+commit a85abfa92220239cad0a8a6b0f2a223f5e6472a9
+Author: Andreas Schwab <schwab@suse.de>
+Date:   Thu Aug 18 11:38:28 2016 +0200
+
+    arm: mark __startcontext as .cantunwind (bug 20435)
+    
+    __startcontext marks the bottom of the call stack of the contexts created
+    by makecontext.
+    
+    (cherry picked from commit 9e2ff6c9cc54c0b4402b8d49e4abe7000fde7617)
+    
+    Also includes the NEWS update, cherry-picked from commits
+    056dd72af83f5459ce6d545a49dea6dba7d635dc and
+    4d047efdbc55b0d68947cde682e5363d16a66294.
+
+diff --git a/sysdeps/unix/sysv/linux/arm/setcontext.S b/sysdeps/unix/sysv/linux/arm/setcontext.S
+index 24c7294..926b65a 100644
+--- a/sysdeps/unix/sysv/linux/arm/setcontext.S
++++ b/sysdeps/unix/sysv/linux/arm/setcontext.S
+@@ -86,12 +86,19 @@ weak_alias(__setcontext, setcontext)
+ 
+ 	/* Called when a makecontext() context returns.  Start the
+ 	   context in R4 or fall through to exit().  */
++	/* Unwind descriptors are looked up based on PC - 2, so we have to
++	   make sure to mark the instruction preceding the __startcontext
++	   label as .cantunwind.  */
++	.fnstart
++	.cantunwind
++	nop
+ ENTRY(__startcontext)
+ 	movs    r0, r4
+ 	bne     PLTJMP(__setcontext)
+ 
+ 	@ New context was 0 - exit
+ 	b       PLTJMP(HIDDEN_JUMPTARGET(exit))
++	.fnend
+ END(__startcontext)
+ 
+ #ifdef PIC

glibc.spec

@@ -273,6 +273,7 @@ Patch1052: glibc-rh1337291.patch
 Patch1053: glibc-build-time.patch
 Patch1054: glibc-rh1352625.patch
 Patch1055: glibc-rh1348620.patch
+Patch1056: glibc-swbz20435.patch
 
 ##############################################################################
 #
@@ -745,6 +746,7 @@ microbenchmark tests on the system.
 %patch1053 -p1
 %patch1054 -p1
 %patch1055 -p1
+%patch1056 -p1
 %patch0059 -p1
 
 ##############################################################################
@@ -1969,6 +1971,7 @@ rm -f *.filelist*
 - Build time improvements
 - Avoid duplicating object files already in libc.a (#1352625)
 - malloc: Avoid premature fallback to mmap (#1348620)
+- CVE-2016-6323: Backtraces can hang on ARM EABI (32-bit) (swbz#20435)
 
 * Thu Jun  2 2016 Florian Weimer <fweimer@redhat.com> - 2.22-17
 - CVE-2016-4429: stack overflow in Sun RPC clntudp_call (#1337140)