Patch "bpf: Fix null pointer dereference in resolve_prog_type() for BPF_PROG_TYPE_EXT" has been added to the 6.1-stable tree

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

    bpf: Fix null pointer dereference in resolve_prog_type() for BPF_PROG_TYPE_EXT

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:
     bpf-fix-null-pointer-dereference-in-resolve_prog_typ.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 3ae588ceab87b271835d808a9c4b30b555fd9fa1
Author: Tengda Wu <wutengda@xxxxxxxxxxxxxxx>
Date:   Thu Jul 11 22:58:18 2024 +0800

    bpf: Fix null pointer dereference in resolve_prog_type() for BPF_PROG_TYPE_EXT
    
    [ Upstream commit f7866c35873377313ff94398f17d425b28b71de1 ]
    
    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@xxxxxxxxxxxxxxx>
    Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
    Acked-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
    Cc: Martin KaFai Lau <kafai@xxxxxx>
    Link: https://lore.kernel.org/bpf/20240711145819.254178-2-wutengda@xxxxxxxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index f080ccf27d256..6a524c5462a6f 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -645,7 +645,7 @@ static inline u32 type_flag(u32 type)
 /* only use after check_attach_btf_id() */
 static inline enum bpf_prog_type resolve_prog_type(const struct bpf_prog *prog)
 {
-	return prog->type == BPF_PROG_TYPE_EXT ?
+	return (prog->type == BPF_PROG_TYPE_EXT && prog->aux->dst_prog) ?
 		prog->aux->dst_prog->type : prog->type;
 }
 




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