bpf: Fix null pointer dereference in resolve_prog_type() for BPF_PROG_TYPE_EXT
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 ]---
One way to fix it is by forcing `attach_prog_fd` non-empty when
bpf_prog_load(). But this will lead to `libbpf_probe_bpf_prog_type`
API broken which use verifier log to probe prog type and will log
nothing if we reject invalid EXT prog before bpf_check().
Another way is by adding null check in resolve_prog_type().
The issue was introduced by commit
4a9c7bbe2ed4 ("bpf: Resolve to
prog->aux->dst_prog->type only for BPF_PROG_TYPE_EXT") which wanted
to correct type resolution for BPF_PROG_TYPE_TRACING programs. Before
that, the type resolution of BPF_PROG_TYPE_EXT prog actually follows
the logic below:
prog->aux->dst_prog ? prog->aux->dst_prog->type : prog->type;
It implies that when EXT program is not yet attached to `dst_prog`,
the prog type should be EXT itself. This code worked fine in the past.
So just keep using it.
Fix this by returning `prog->type` for BPF_PROG_TYPE_EXT if `dst_prog`
is not present in resolve_prog_type().
Fixes: 4a9c7bbe2ed4 ("bpf: Resolve to prog->aux->dst_prog->type only for BPF_PROG_TYPE_EXT")
Signed-off-by: Tengda Wu <wutengda@huaweicloud.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20240711145819.254178-2-wutengda@huaweicloud.com
projects / linux.git / commit