This is a note to let you know that I've just added the patch titled bpf: Fix out of bounds access from invalid *_or_null type verification to the 5.10-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-out-of-bounds-access-from-invalid-_or_null-type-verification.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 51cf0a9e6f1c842efa768d3079b16a80cbf871c3 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Date: Tue, 4 Jan 2022 14:16:03 +0000 Subject: bpf: Fix out of bounds access from invalid *_or_null type verification From: Daniel Borkmann <daniel@xxxxxxxxxxxxx> [ no upstream commit given implicitly fixed through the larger refactoring in c25b2ae136039ffa820c26138ed4a5e5f3ab3841 ] While auditing some other code, I noticed missing checks inside the pointer arithmetic simulation, more specifically, adjust_ptr_min_max_vals(). Several *_OR_NULL types are not rejected whereas they are _required_ to be rejected given the expectation is that they get promoted into a 'real' pointer type for the success case, that is, after an explicit != NULL check. One case which stands out and is accessible from unprivileged (iff enabled given disabled by default) is BPF ring buffer. From crafting a PoC, the NULL check can be bypassed through an offset, and its id marking will then lead to promotion of mem_or_null to a mem type. bpf_ringbuf_reserve() helper can trigger this case through passing of reserved flags, for example. func#0 @0 0: R1=ctx(id=0,off=0,imm=0) R10=fp0 0: (7a) *(u64 *)(r10 -8) = 0 1: R1=ctx(id=0,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm 1: (18) r1 = 0x0 3: R1_w=map_ptr(id=0,off=0,ks=0,vs=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm 3: (b7) r2 = 8 4: R1_w=map_ptr(id=0,off=0,ks=0,vs=0,imm=0) R2_w=invP8 R10=fp0 fp-8_w=mmmmmmmm 4: (b7) r3 = 0 5: R1_w=map_ptr(id=0,off=0,ks=0,vs=0,imm=0) R2_w=invP8 R3_w=invP0 R10=fp0 fp-8_w=mmmmmmmm 5: (85) call bpf_ringbuf_reserve#131 6: R0_w=mem_or_null(id=2,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 6: (bf) r6 = r0 7: R0_w=mem_or_null(id=2,ref_obj_id=2,off=0,imm=0) R6_w=mem_or_null(id=2,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 7: (07) r0 += 1 8: R0_w=mem_or_null(id=2,ref_obj_id=2,off=1,imm=0) R6_w=mem_or_null(id=2,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 8: (15) if r0 == 0x0 goto pc+4 R0_w=mem(id=0,ref_obj_id=0,off=0,imm=0) R6_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 9: R0_w=mem(id=0,ref_obj_id=0,off=0,imm=0) R6_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 9: (62) *(u32 *)(r6 +0) = 0 R0_w=mem(id=0,ref_obj_id=0,off=0,imm=0) R6_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 10: R0_w=mem(id=0,ref_obj_id=0,off=0,imm=0) R6_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 10: (bf) r1 = r6 11: R0_w=mem(id=0,ref_obj_id=0,off=0,imm=0) R1_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R6_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 11: (b7) r2 = 0 12: R0_w=mem(id=0,ref_obj_id=0,off=0,imm=0) R1_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R2_w=invP0 R6_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 12: (85) call bpf_ringbuf_submit#132 13: R6=invP(id=0) R10=fp0 fp-8=mmmmmmmm 13: (b7) r0 = 0 14: R0_w=invP0 R6=invP(id=0) R10=fp0 fp-8=mmmmmmmm 14: (95) exit from 8 to 13: safe processed 15 insns (limit 1000000) max_states_per_insn 0 total_states 1 peak_states 1 mark_read 0 OK All three commits, that is b121b341e598 ("bpf: Add PTR_TO_BTF_ID_OR_NULL support"), 457f44363a88 ("bpf: Implement BPF ring buffer and verifier support for it"), and the afbf21dce668 ("bpf: Support readonly/readwrite buffers in verifier") suffer the same cause and their *_OR_NULL type pendants must be rejected in adjust_ptr_min_max_vals(). Make the test more robust by reusing reg_type_may_be_null() helper such that we catch all *_OR_NULL types we have today and in future. Note that pointer arithmetic on PTR_TO_BTF_ID, PTR_TO_RDONLY_BUF, and PTR_TO_RDWR_BUF is generally allowed. Fixes: b121b341e598 ("bpf: Add PTR_TO_BTF_ID_OR_NULL support") Fixes: 457f44363a88 ("bpf: Implement BPF ring buffer and verifier support for it") Fixes: afbf21dce668 ("bpf: Support readonly/readwrite buffers in verifier") Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/bpf/verifier.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6037,16 +6037,16 @@ static int adjust_ptr_min_max_vals(struc fallthrough; case PTR_TO_PACKET_END: case PTR_TO_SOCKET: - case PTR_TO_SOCKET_OR_NULL: case PTR_TO_SOCK_COMMON: - case PTR_TO_SOCK_COMMON_OR_NULL: case PTR_TO_TCP_SOCK: - case PTR_TO_TCP_SOCK_OR_NULL: case PTR_TO_XDP_SOCK: +reject: verbose(env, "R%d pointer arithmetic on %s prohibited\n", dst, reg_type_str[ptr_reg->type]); return -EACCES; default: + if (reg_type_may_be_null(ptr_reg->type)) + goto reject; break; } Patches currently in stable-queue which might be from daniel@xxxxxxxxxxxxx are queue-5.10/bpf-fix-out-of-bounds-access-from-invalid-_or_null-type-verification.patch