Fix BZ 20419. A PT_NOTE in a binary could be arbitratily large, so using

alloca for it may cause stack overflow.  If the note is larger than
__MAX_ALLOCA_CUTOFF, use dynamically allocated memory to read it in.

2018-05-05  Paul Pluzhnikov  <ppluzhnikov@google.com>

	[BZ #20419]
	* elf/dl-load.c (open_verify): Fix stack overflow.
	* elf/Makefile (tst-big-note): New test.
	* elf/tst-big-note-lib.S: New.
	* elf/tst-big-note.c: New.

4 files changed, 77 insertions, 4 deletions

diff --git a/elf/Makefile b/elf/Makefile
index e658928..2dcd2b8 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -186,7 +186,7 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
 	 tst-tlsalign tst-tlsalign-extern tst-nodelete-opened \
 	 tst-nodelete2 tst-audit11 tst-audit12 tst-dlsym-error tst-noload \
 	 tst-latepthread tst-tls-manydynamic tst-nodelete-dlclose \
-	 tst-debug1 tst-main1 tst-absolute-sym
+	 tst-debug1 tst-main1 tst-absolute-sym tst-big-note
 #	 reldep9
 tests-internal += loadtest unload unload2 circleload1 \
 	 neededtest neededtest2 neededtest3 neededtest4 \
@@ -272,7 +272,9 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
 		tst-audit12mod1 tst-audit12mod2 tst-audit12mod3 tst-auditmod12 \
 		tst-latepthreadmod $(tst-tls-many-dynamic-modules) \
 		tst-nodelete-dlclose-dso tst-nodelete-dlclose-plugin \
-		tst-main1mod tst-libc_dlvsym-dso tst-absolute-sym-lib
+		tst-main1mod tst-libc_dlvsym-dso tst-absolute-sym-lib \
+		tst-big-note-lib
+
 ifeq (yes,$(have-mtls-dialect-gnu2))
 tests += tst-gnu2-tls1
 modules-names += tst-gnu2-tls1mod
@@ -1450,3 +1452,5 @@ $(objpfx)tst-libc_dlvsym-static: $(common-objpfx)dlfcn/libdl.a
 tst-libc_dlvsym-static-ENV = \
   LD_LIBRARY_PATH=$(objpfx):$(common-objpfx):$(common-objpfx)dlfcn
 $(objpfx)tst-libc_dlvsym-static.out: $(objpfx)tst-libc_dlvsym-dso.so
+
+$(objpfx)tst-big-note: $(objpfx)tst-big-note-lib.so
diff --git a/elf/dl-load.c b/elf/dl-load.c
index a5e3a25..4312369 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1462,6 +1462,7 @@ open_verify (const char *name, int fd,
       ElfW(Ehdr) *ehdr;
       ElfW(Phdr) *phdr, *ph;
       ElfW(Word) *abi_note;
+      ElfW(Word) *abi_note_malloced = NULL;
       unsigned int osversion;
       size_t maplength;
 
@@ -1633,10 +1634,25 @@ open_verify (const char *name, int fd,
 	      abi_note = (void *) (fbp->buf + ph->p_offset);
 	    else
 	      {
-		abi_note = alloca (size);
+		/* Note: __libc_use_alloca is not usable here, because
+		   thread info may not have been set up yet.  */
+		if (size < __MAX_ALLOCA_CUTOFF)
+		  abi_note = alloca (size);
+		else
+		  {
+		    /* There could be multiple PT_NOTEs.  */
+		    abi_note_malloced = realloc (abi_note_malloced, size);
+		    if (abi_note_malloced == NULL)
+		      goto read_error;
+
+		    abi_note = abi_note_malloced;
+		  }
 		__lseek (fd, ph->p_offset, SEEK_SET);
 		if (__libc_read (fd, (void *) abi_note, size) != size)
-		  goto read_error;
+		  {
+		    free (abi_note_malloced);
+		    goto read_error;
+		  }
 	      }
 
 	    while (memcmp (abi_note, &expected_note, sizeof (expected_note)))
@@ -1671,6 +1687,7 @@ open_verify (const char *name, int fd,
 
 	    break;
 	  }
+      free (abi_note_malloced);
     }
 
   return fd;
diff --git a/elf/tst-big-note-lib.S b/elf/tst-big-note-lib.S
new file mode 100644
index 0000000..6b514a0
--- /dev/null
+++ b/elf/tst-big-note-lib.S
@@ -0,0 +1,26 @@
+/* Bug 20419: test for stack overflow in elf/dl-load.c open_verify()
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* This creates a .so with 8MiB PT_NOTE segment.
+   On a typical Linux system with 8MiB "ulimit -s", that was enough
+   to trigger stack overflow in open_verify.  */
+
+.pushsection .note.big,"a"
+.balign 4
+.fill 8*1024*1024, 1, 0
+.popsection
diff --git a/elf/tst-big-note.c b/elf/tst-big-note.c
new file mode 100644
index 0000000..fcd2b0e
--- /dev/null
+++ b/elf/tst-big-note.c
@@ -0,0 +1,26 @@
+/* Bug 20419: test for stack overflow in elf/dl-load.c open_verify()
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* This file must be run from within a directory called "elf".  */
+
+int main (int argc, char *argv[])
+{
+  /* Nothing to do here: merely linking against tst-big-note-lib.so triggers
+     the bug.  */
+  return 0;
+}