Patch "libbpf: Prevent null-pointer dereference when prog to load has no BTF" has been added to the 6.8-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    libbpf: Prevent null-pointer dereference when prog to load has no BTF

to the 6.8-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-prevent-null-pointer-dereference-when-prog-to.patch
and it can be found in the queue-6.8 subdirectory.

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



commit 6149a8ab763e36efd64659422698faa0b7138350
Author: Quentin Monnet <qmo@xxxxxxxxxx>
Date:   Thu Mar 14 15:04:38 2024 +0000

    libbpf: Prevent null-pointer dereference when prog to load has no BTF
    
    [ Upstream commit 9bf48fa19a4b1d186e08b20bf7e5de26a15644fb ]
    
    In bpf_objec_load_prog(), there's no guarantee that obj->btf is non-NULL
    when passing it to btf__fd(), and this function does not perform any
    check before dereferencing its argument (as bpf_object__btf_fd() used to
    do). As a consequence, we get segmentation fault errors in bpftool (for
    example) when trying to load programs that come without BTF information.
    
    v2: Keep btf__fd() in the fix instead of reverting to bpf_object__btf_fd().
    
    Fixes: df7c3f7d3a3d ("libbpf: make uniform use of btf__fd() accessor inside libbpf")
    Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
    Signed-off-by: Quentin Monnet <qmo@xxxxxxxxxx>
    Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
    Link: https://lore.kernel.org/bpf/20240314150438.232462-1-qmo@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 92bca96587a4a..5af9cab422ca3 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -7456,9 +7456,9 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
 	char *cp, errmsg[STRERR_BUFSIZE];
 	size_t log_buf_size = 0;
 	char *log_buf = NULL, *tmp;
-	int btf_fd, ret, err;
 	bool own_log_buf = true;
 	__u32 log_level = prog->log_level;
+	int ret, err;
 
 	if (prog->type == BPF_PROG_TYPE_UNSPEC) {
 		/*
@@ -7482,9 +7482,8 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
 	load_attr.prog_ifindex = prog->prog_ifindex;
 
 	/* specify func_info/line_info only if kernel supports them */
-	btf_fd = btf__fd(obj->btf);
-	if (btf_fd >= 0 && kernel_supports(obj, FEAT_BTF_FUNC)) {
-		load_attr.prog_btf_fd = btf_fd;
+	if (obj->btf && btf__fd(obj->btf) >= 0 && kernel_supports(obj, FEAT_BTF_FUNC)) {
+		load_attr.prog_btf_fd = btf__fd(obj->btf);
 		load_attr.func_info = prog->func_info;
 		load_attr.func_info_rec_size = prog->func_info_rec_size;
 		load_attr.func_info_cnt = prog->func_info_cnt;