[binutils-gdb] [gdb/tdep] Fix use-after-free in arm_exidx_fill_cache

[binutils-gdb] [gdb/tdep] Fix use-after-free in arm_exidx_fill_cache

[Tom de Vries]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=bae2a57f4c07f46093e7bf00fec2554868e77189

commit bae2a57f4c07f46093e7bf00fec2554868e77189
Author: Tom de Vries <tdevries@suse.de>
Date:   Mon Feb 5 11:04:06 2024 +0100

    [gdb/tdep] Fix use-after-free in arm_exidx_fill_cache
    
    On arm-linux the linaro CI occasionally reports:
    ...
     (gdb) up 10
     #4  0x0001b864 in pthread_join ()
     (gdb) FAIL: gdb.threads/staticthreads.exp: up 10
    ...
    while this is expected:
    ...
     (gdb) up 10
     #3  0x00010568 in main (argc=1, argv=0xfffeede4) at staticthreads.c:76
     76          pthread_join (thread, NULL);
     (gdb) PASS: gdb.threads/staticthreads.exp: up 10
    ...
    
    Thiago investigated the problem, and using valgrind found an invalid read in
    arm_exidx_fill_cache.
    
    The problem happens as follows:
    - an objfile and corresponding per_bfd are allocated
    - some memory is allocated in arm_exidx_new_objfile using
      objfile->objfile_obstack, for the "exception table entry cache".
    - a symbol reread is triggered, and the objfile, including the
      objfile_obstack, is destroyed
    - a new objfile is allocated, using the same per_bfd
    - again arm_exidx_new_objfile is called, but since the same per_bfd is used,
      it doesn't allocate any new memory for the "exception table entry cache".
    - the "exception table entry cache" is accessed by arm_exidx_fill_cache,
      and we have a use-after-free.
    
    This is a regression since commit a2726d4ff80 ("[ARM] Store exception handling
    information per-bfd instead of per-objfile"), which changed the "exception
    table entry cache" from per-objfile to per-bfd, but failed to update the
    obstack_alloc.
    
    Fix this by using objfile->per_bfd->storage_obstack instead of
    objfile->objfile_obstack.
    
    I couldn't reproduce the FAIL myself, but Thiago confirmed that the patch
    fixes it.
    
    Tested on arm-linux.
    
    Approved-By: Luis Machado <luis.machado@arm.com>
    
    PR tdep/31254
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31254

Diff:
---
 gdb/arm-tdep.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
index 0d0431e0d1c..861d50a6a3b 100644
--- a/gdb/arm-tdep.c
+++ b/gdb/arm-tdep.c
@@ -2701,7 +2701,7 @@ arm_exidx_new_objfile (struct objfile *objfile)
       if (n_bytes || n_words)
 	{
 	  gdb_byte *p = entry
-	    = (gdb_byte *) obstack_alloc (&objfile->objfile_obstack,
+	    = (gdb_byte *) obstack_alloc (&objfile->per_bfd->storage_obstack,
 					  n_bytes + n_words * 4 + 1);
 
 	  while (n_bytes--)