[glibc] elf: Verify the tunable cache header signature and version

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=4e971f555850f856e70ceb05d963baa9e0a455a4

commit 4e971f555850f856e70ceb05d963baa9e0a455a4
Author: Adhemerval Zanella <[email protected]>
Date:   Mon Jul 6 16:56:27 2026 -0300

    elf: Verify the tunable cache header signature and version
    
    The tunable header signature and version are written by ldconfig but
    never checked them on read, so the version field was inert.  Reject
    the section unless both match.
    
    Checked on x86_64-linux-gnu and i686-linux-gnu.
    
    Reviewed-by: DJ Delorie <[email protected]>

Diff:
---
 elf/dl-cache.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/elf/dl-cache.c b/elf/dl-cache.c
index 5d8d3cae90..498196d0aa 100644
--- a/elf/dl-cache.c
+++ b/elf/dl-cache.c
@@ -642,6 +642,11 @@ _dl_load_cache_tunables (const char **data)
 
   thc = (struct tunable_header_cached *)
     ext.sections[cache_extension_tag_tunables].base;
+
+  /* Reject data produced by a different tunable cache format.  */
+  if (thc->signature != TUNCONF_SIGNATURE || thc->version != TUNCONF_VERSION)
+    return NULL;
+
   tec = thc->tunables;
   count = thc->num_tunables;