Patch "libbpf: Checking the btf_type kind when fixing variable offsets" has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    libbpf: Checking the btf_type kind when fixing variable offsets

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     libbpf-checking-the-btf_type-kind-when-fixing-variab.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 5c6ad24635636763fb23a02e95013ae59f973989
Author: Donglin Peng <dolinux.peng@xxxxxxxxx>
Date:   Wed Jun 19 05:23:55 2024 -0700

    libbpf: Checking the btf_type kind when fixing variable offsets
    
    [ Upstream commit cc5083d1f3881624ad2de1f3cbb3a07e152cb254 ]
    
    I encountered an issue when building the test_progs from the repository [1]:
    
      $ pwd
      /work/Qemu/x86_64/linux-6.10-rc2/tools/testing/selftests/bpf/
    
      $ make test_progs V=1
      [...]
      ./tools/sbin/bpftool gen object ./ip_check_defrag.bpf.linked2.o ./ip_check_defrag.bpf.linked1.o
      libbpf: failed to find symbol for variable 'bpf_dynptr_slice' in section '.ksyms'
      Error: failed to link './ip_check_defrag.bpf.linked1.o': No such file or directory (2)
      [...]
    
    Upon investigation, I discovered that the btf_types referenced in the '.ksyms'
    section had a kind of BTF_KIND_FUNC instead of BTF_KIND_VAR:
    
      $ bpftool btf dump file ./ip_check_defrag.bpf.linked1.o
      [...]
      [2] DATASEC '.ksyms' size=0 vlen=2
            type_id=16 offset=0 size=0 (FUNC 'bpf_dynptr_from_skb')
            type_id=17 offset=0 size=0 (FUNC 'bpf_dynptr_slice')
      [...]
      [16] FUNC 'bpf_dynptr_from_skb' type_id=82 linkage=extern
      [17] FUNC 'bpf_dynptr_slice' type_id=85 linkage=extern
      [...]
    
    For a detailed analysis, please refer to [2]. We can add a kind checking to
    fix the issue.
    
      [1] https://github.com/eddyz87/bpf/tree/binsort-btf-dedup
      [2] https://lore.kernel.org/all/0c0ef20c-c05e-4db9-bad7-2cbc0d6dfae7@xxxxxxxxxx/
    
    Fixes: 8fd27bf69b86 ("libbpf: Add BPF static linker BTF and BTF.ext support")
    Signed-off-by: Donglin Peng <dolinux.peng@xxxxxxxxx>
    Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
    Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
    Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
    Link: https://lore.kernel.org/bpf/20240619122355.426405-1-dolinux.peng@xxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index 4ac02c28e152a..8a7cb830bff14 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -2189,10 +2189,17 @@ static int linker_fixup_btf(struct src_obj *obj)
 		vi = btf_var_secinfos(t);
 		for (j = 0, m = btf_vlen(t); j < m; j++, vi++) {
 			const struct btf_type *vt = btf__type_by_id(obj->btf, vi->type);
-			const char *var_name = btf__str_by_offset(obj->btf, vt->name_off);
-			int var_linkage = btf_var(vt)->linkage;
+			const char *var_name;
+			int var_linkage;
 			Elf64_Sym *sym;
 
+			/* could be a variable or function */
+			if (!btf_is_var(vt))
+				continue;
+
+			var_name = btf__str_by_offset(obj->btf, vt->name_off);
+			var_linkage = btf_var(vt)->linkage;
+
 			/* no need to patch up static or extern vars */
 			if (var_linkage != BTF_VAR_GLOBAL_ALLOCATED)
 				continue;