GNU C Library master sources branch release/2.22/master updated. glibc-2.22-85-ga85abfa

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http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=a85abfa92220239cad0a8a6b0f2a223f5e6472a9

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/ChangeLog b/ChangeLog
index 618515e..c2a91e1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2016-08-15  Andreas Schwab  <schwab@suse.de>
+
+	[BZ #20435]
+	* sysdeps/unix/sysv/linux/arm/setcontext.S (__startcontext): Mark
+	as .cantunwind.
+
 2016-06-21  Florian Weimer  <fweimer@redhat.com>
 
 	[BZ #20284]
diff --git a/NEWS b/NEWS
index 923468d..a19f656 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,12 @@ using `glibc' in the "product" field.
 
 Version 2.22.1
 
+* On ARM EABI (32-bit), generating a backtrace for execution contexts which
+  have been created with makecontext could fail to terminate due to a
+  missing .cantunwind annotation.  This has been observed to lead to a hang
+  (denial of service) in some Go applications compiled with gccgo.  Reported
+  by Andreas Schwab.  (CVE-2016-6323)
+
 * A stack-based buffer overflow was found in libresolv when invoked from
   libnss_dns, allowing specially crafted DNS responses to seize control
   of execution flow in the DNS client.  The buffer overflow occurs in
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

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                                |    6 ++++++
 NEWS                                     |    6 ++++++
 sysdeps/unix/sysv/linux/arm/setcontext.S |    7 +++++++
 3 files changed, 19 insertions(+), 0 deletions(-)


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