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From: "vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug gdb/31040] New: [gdb] Make auxv parsing more strict
Date: Tue, 07 Nov 2023 16:01:32 +0000
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X-Bugzilla-Component: gdb
X-Bugzilla-Version: HEAD
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D31040

            Bug ID: 31040
           Summary: [gdb] Make auxv parsing more strict
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

[ See also
https://sourceware.org/pipermail/gdb-patches/2023-November/203763.html ]

The parsing of auxv is forgiving to the point that reading it with the wrong
word size (4 instead of 8) may still yield the expected result.

This is an example of making it more careful:
...
diff --git a/gdb/auxv.c b/gdb/auxv.c
index 61acd48fc98..563cf173a23 100644
--- a/gdb/auxv.c
+++ b/gdb/auxv.c
@@ -395,6 +395,19 @@ target_auxv_search (const gdb::byte_vector &auxv,
target_ops *ops,
     switch (parse_auxv (ops, gdbarch, &ptr, data + len, &type, &val))
       {
       case 1:                  /* Here's an entry, check it.  */
+       if (type =3D=3D AT_NULL)
+         {
+           if (ptr =3D=3D data + len)
+             {
+               /* AT_NULL found, as last entry.  */
+               return 0;
+             }
+           else
+             {
+               /* AT_NULL found, not as last entry.  */
+               return -1;
+             }
+         }
        if (type =3D=3D match)
          {
            *valp =3D val;
@@ -402,7 +415,8 @@ target_auxv_search (const gdb::byte_vector &auxv,
target_ops *ops,
          }
        break;
       case 0:                  /* End of the vector.  */
-       return 0;
+       /* No AT_NULL found.  */
+       return -1;
       default:                 /* Bogosity.  */
        return -1;
       }
...

In other words, it returns -1 more often.  Of course that has no effect if
callers don't care if -1 is returned, so there may be work to do there as w=
ell.

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