When loading a EXT program without specifying `attr->attach_prog_fd`,
the `prog->aux->dst_prog` will be null. At this time, calling
resolve_prog_type() anywhere will result in a null pointer dereference.
Example stack trace:
[ 8.107863] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000004
[ 8.108262] Mem abort info:
[ 8.108384] ESR = 0x0000000096000004
[ 8.108547] EC = 0x25: DABT (current EL), IL = 32 bits
[ 8.108722] SET = 0, FnV = 0
[ 8.108827] EA = 0, S1PTW = 0
[ 8.108939] FSC = 0x04: level 0 translation fault
[ 8.109102] Data abort info:
[ 8.109203] ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
[ 8.109399] CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[ 8.109614] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[ 8.109836] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000101354000
[ 8.110011] [0000000000000004] pgd=0000000000000000, p4d=0000000000000000
[ 8.112624] Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
[ 8.112783] Modules linked in:
[ 8.113120] CPU: 0 PID: 99 Comm: may_access_dire Not tainted 6.10.0-rc3-next-20240613-dirty #1
[ 8.113230] Hardware name: linux,dummy-virt (DT)
[ 8.113390] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 8.113429] pc : may_access_direct_pkt_data+0x24/0xa0
[ 8.113746] lr : add_subprog_and_kfunc+0x634/0x8e8
[ 8.113798] sp : ffff80008283b9f0
[ 8.113813] x29: ffff80008283b9f0 x28: ffff800082795048 x27: 0000000000000001
[ 8.113881] x26: ffff0000c0bb2600 x25: 0000000000000000 x24: 0000000000000000
[ 8.113897] x23: ffff0000c1134000 x22: 000000000001864f x21: ffff0000c1138000
[ 8.113912] x20: 0000000000000001 x19: ffff0000c12b8000 x18: ffffffffffffffff
[ 8.113929] x17: 0000000000000000 x16: 0000000000000000 x15: 0720072007200720
[ 8.113944] x14: 0720072007200720 x13: 0720072007200720 x12: 0720072007200720
[ 8.113958] x11: 0720072007200720 x10: 0000000000f9fca4 x9 : ffff80008021f4e4
[ 8.113991] x8 : 0101010101010101 x7 : 746f72705f6d656d x6 : 000000001e0e0f5f
[ 8.114006] x5 : 000000000001864f x4 : ffff0000c12b8000 x3 : 000000000000001c
[ 8.114020] x2 : 0000000000000002 x1 : 0000000000000000 x0 : 0000000000000000
[ 8.114126] Call trace:
[ 8.114159] may_access_direct_pkt_data+0x24/0xa0
[ 8.114202] bpf_check+0x3bc/0x28c0
[ 8.114214] bpf_prog_load+0x658/0xa58
[ 8.114227] __sys_bpf+0xc50/0x2250
[ 8.114240] __arm64_sys_bpf+0x28/0x40
[ 8.114254] invoke_syscall.constprop.0+0x54/0xf0
[ 8.114273] do_el0_svc+0x4c/0xd8
[ 8.114289] el0_svc+0x3c/0x140
[ 8.114305] el0t_64_sync_handler+0x134/0x150
[ 8.114331] el0t_64_sync+0x168/0x170
[ 8.114477] Code: 7100707f 54000081 f9401c00 f9403800 (b9400403)
[ 8.118672] ---[ end trace 0000000000000000 ]---
Fix this by adding dst_prog non-empty check in BPF_PROG_TYPE_EXT case
when calling bpf_prog_load().
Note the BPF_PROG_TYPE_EXT type detection in libbpf also needs to be
adapted by passing a valid attach_prog_fd, since an empty attach_prog_fd
is no longer allowed when loading EXT program.
Fixes: 4a9c7bbe2ed4 ("bpf: Resolve to prog->aux->dst_prog->type only for BPF_PROG_TYPE_EXT")
Signed-off-by: Tengda Wu <wutengda@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v5.18+
---
v2: Fix libbpf_probe_prog_types test failure reported by CI by adapting
libbpf code. (thanks for jirka's reminder)
v1: https://lore.kernel.org/all/20240620060701.1465291-1-wutengda@xxxxxxxxxxxxxxx/
kernel/bpf/syscall.c | 5 ++++-
tools/lib/bpf/libbpf_probes.c | 13 ++++++++++++-
2 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index f45ed6adc092..4490f8ccf006 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2632,9 +2632,12 @@ bpf_prog_load_check_attach(enum bpf_prog_type prog_type,
return 0;
return -EINVAL;
case BPF_PROG_TYPE_SYSCALL:
- case BPF_PROG_TYPE_EXT:
if (expected_attach_type)
return -EINVAL;
+ return 0;
+ case BPF_PROG_TYPE_EXT:
+ if (expected_attach_type || !dst_prog)
+ return -EINVAL;
fallthrough;
default:
return 0;
diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
index 9dfbe7750f56..37f87c824933 100644
--- a/tools/lib/bpf/libbpf_probes.c
+++ b/tools/lib/bpf/libbpf_probes.c
@@ -112,6 +112,7 @@ static int probe_prog_load(enum bpf_prog_type prog_type,
int fd, err, exp_err = 0;
const char *exp_msg = NULL;
char buf[4096];
+ int attach_prog_fd = -1;
switch (prog_type) {
case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
@@ -148,9 +149,17 @@ static int probe_prog_load(enum bpf_prog_type prog_type,
opts.log_size = sizeof(buf);
opts.log_level = 1;
opts.attach_btf_id = 1;
+ /* choose socket_filter as the target program to attach, since it
+ * is the earliest and most likely BPF program to be supported.
+ */
+ attach_prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, NULL,
+ "GPL", insns, insns_cnt, NULL);
+ if (attach_prog_fd < 0)
+ return attach_prog_fd;
+ opts.attach_prog_fd = attach_prog_fd;
exp_err = -EINVAL;
- exp_msg = "Cannot replace kernel functions";
+ exp_msg = "FENTRY/FEXIT program can only be attached to another program annotated with BTF";
break;
case BPF_PROG_TYPE_SYSCALL:
opts.prog_flags = BPF_F_SLEEPABLE;
@@ -192,6 +201,8 @@ static int probe_prog_load(enum bpf_prog_type prog_type,
err = -errno;
if (fd >= 0)
close(fd);
+ if (attach_prog_fd >= 0)
+ close(attach_prog_fd);
if (exp_err) {
if (fd >= 0 || err != exp_err)
return 0;
--
2.34.1
