[Bug libc/25729] New: Invalid Pointer Arithmetic in g_path_get_basename

["fabien.lheureux@trust-in-soft.com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=25729

            Bug ID: 25729
           Summary: Invalid Pointer Arithmetic in g_path_get_basename
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: fabien.lheureux@trust-in-soft.com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

## Analysis Context

*The verification was performed with TrustInSoft Analyzer, a formal
static analyzer for C and C++.*

*The result is part of a larger security assessment performed by
TrustInSoft for* ***Naval Group***.

This issue was found during the analysis of wireshark, and the analysis of
wireshark was performed in the following environment:

----------------- ----------------------------------------------
Platform          Ubuntu Linux 18.04
Tool              TrustInSoft Analyzer, a formal static analyzer
Input Files       Fuzzing of 10 000 pcap file using AFL
Verification      Analysis of `process_cap_file` with the AFL corpus
------------- ----------------------------------------------

------------ ------------------- ---------------------- ----------------
Wireshark    version v2.6.16rc0  git commit dcd65a4012 
https://github.com/wireshark/wireshark.git
glib         version 2.62.6      git commit eb0f73a39  
https://github.com/GNOME/glib.git
libgcrypt    version 1.8.5       git commit ada758e3   
https://github.com/gpg/libgcrypt.git
libgpg-error version 1.37        git commit 85b5006    
https://github.com/gpg/libgpg-error.git
libpcap      version 1.9.1       git commit 1547215c   
https://github.com/the-tcpdump-group/libpcap.git
pcre         version 8.43-RC1    git commit 10e4adb    
https://github.com/svn2github/pcre.git
pcre2        version 10.10       git commit a677f5b    
https://github.com/luvit/pcre2.git
zlib         version 10.10       git commit a677f5b    
https://github.com/madler/zlib.git
------------ ------------------- ---------------------- ----------------

- valgrind is deactivated in glib
- PCRE library is deactivated in glib
- `cap_files_hashes` is deactivated in wireshark

## Invalid Pointer Arithmetic in *g_path_get_basename*

In the function `g_path_get_basename`, the expression `file_name +
base + 1` may computes an invalid pointer when `base` is equal to `-1`
and the evaluation of the expression is performed as `(file_name +
base) + 1`.

File: glib/glib/gfileutils.c

```c
memcpy (retval, file_name + base + 1, len);
```

With the following patch, no invalid pointer is computed.


```c
memcpy (retval, file_name + (base + 1), len);
```

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