[binutils-gdb] libctf: strtab corruption when strings are added to ctf_open()ed dicts

[Nick Alcock]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=1cdcc977329d8729745ad5f1389a39b9dc423754

commit 1cdcc977329d8729745ad5f1389a39b9dc423754
Author: Nick Alcock <nick.alcock@oracle.com>
Date:   Tue Jun 11 19:37:54 2024 +0100

    libctf: strtab corruption when strings are added to ctf_open()ed dicts
    
    ctf_str_add_ref and ctf_str_add_movable_ref take a string and are supposed
    to return a strtab offset.  These offsets are "provisional": the ref
    mechanism records the address of the location in which the ref is stored and
    modifies it when the strtab is finally written out.  Provisional refs in new
    dicts start at 0 and go up via strlen() as new refs are added: this is fine,
    because the strtab is empty and none of these values will overlap any
    existing string offsets (since there are none).  Unfortunately, when a dict
    is ctf_open()ed, we fail to set the initial provisional strtab offset to a
    higher value than any existing string offset: it starts at zero again!
    It's a shame that we already *have* strings at those offsets...
    
    This is all fixed up once the string is reserialized, but if you look up
    newly-added strings before serialization, you get corrupted partial string
    results from the existing ctf_open()ed dict.
    
    Observed (and thus regtested) by an upcoming test (in this patch series).
    
    Exposed by the recently-introduced series that permits modification of
    ctf_open()ed dicts, which has not been released anywhere.  Before that,
    any attempt to do such things would fail with ECTF_RDONLY.
    
    libctf/
            * ctf-string.c (ctf_str_create_atoms): Initialize
            ctf_str_prov_offset.

Diff:
---
 libctf/ctf-string.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libctf/ctf-string.c b/libctf/ctf-string.c
index 0c5bd58cdaf..2d96e45617c 100644
--- a/libctf/ctf-string.c
+++ b/libctf/ctf-string.c
@@ -195,6 +195,8 @@ ctf_str_create_atoms (ctf_dict_t *fp)
       atom->csa_offset = i;
     }
 
+  fp->ctf_str_prov_offset = fp->ctf_str[CTF_STRTAB_0].cts_len + 1;
+
   return 0;
 
  oom_str_add: