[Valgrind-developers] [valgrind] Bug 496571 - False positive for null key passed to bpf_map_get_next_key syscall.

[Paul F. <pa...@so...>]

https://sourceware.org/git/gitweb.cgi?p=valgrind.git;h=75ca7437c97a703b7a729d8694743ddde3762713

commit 75ca7437c97a703b7a729d8694743ddde3762713
Author: Ryan Mack <rm...@up...>
Date:   Sat Nov 23 18:02:21 2024 +0100

    Bug 496571 - False positive for null key passed to bpf_map_get_next_key syscall.
    
    No regtest added because BPF requires privileges. See the bugzilla item
    for example usage.

Diff:
---
 NEWS                                | 1 +
 coregrind/m_syswrap/syswrap-linux.c | 6 +++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/NEWS b/NEWS
index eb853a0bd3..ad5fa1a417 100644
--- a/NEWS
+++ b/NEWS
@@ -26,6 +26,7 @@ are not entered into bugzilla tend to get forgotten about or ignored.
 494327  Crash when running Helgrind built with #define TRACE_PTH_FNS 1
 494337  All threaded applications cause still holding lock errors
 495488  Add FreeBSD getrlimitusage syscall wrapper
+496571  False positive for null key passed to bpf_map_get_next_key syscall.
 
 To see details of a given bug, visit
   https://bugs.kde.org/show_bug.cgi?id=XXXXXX
diff --git a/coregrind/m_syswrap/syswrap-linux.c b/coregrind/m_syswrap/syswrap-linux.c
index 177712117c..775fae75b2 100644
--- a/coregrind/m_syswrap/syswrap-linux.c
+++ b/coregrind/m_syswrap/syswrap-linux.c
@@ -12993,7 +12993,11 @@ PRE(sys_bpf)
             }
             /* Get size of key for this map. */
             if (bpf_map_get_sizes(attr->map_fd, &key_size, &value_size)) {
-               PRE_MEM_READ("bpf(attr->key)", attr->key, key_size);
+               /* see https://bugs.kde.org/show_bug.cgi?id=496571 */
+               /* Key is null when getting first entry in map. */
+               if (attr->key) {
+                  PRE_MEM_READ("bpf(attr->key)", attr->key, key_size);
+               }
                PRE_MEM_WRITE("bpf(attr->next_key)", attr->next_key, key_size);
             }
          }