From a66c81bcad4a3252f031588838d00e7ddaa7ad87 Mon Sep 17 00:00:00 2001 From: Piotr Krysiuk Date: Tue, 23 Mar 2021 21:28:00 +0100 Subject: [PATCH] bpf: Add sanity check for upper ptr_limit BugLink: https://bugs.launchpad.net/bugs/1920995 Given we know the max possible value of ptr_limit at the time of retrieving the latter, add basic assertions, so that the verifier can bail out if anything looks odd and reject the program. Nothing triggered this so far, but it also does not hurt to have these. Signed-off-by: Piotr Krysiuk Co-developed-by: Daniel Borkmann Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov (cherry picked from commit 1b1597e64e1a610c7a96710fc4717158e98a08b3 net.git) Signed-off-by: Thadeu Lima de Souza Cascardo Acked-by: Kamal Mostafa Acked-by: Kelsey Skunberg Signed-off-by: Stefan Bader --- kernel/bpf/verifier.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index aaec49eb4f87d..9d413f7dffac7 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -4914,10 +4914,14 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, { bool mask_to_left = (opcode == BPF_ADD && off_is_neg) || (opcode == BPF_SUB && !off_is_neg); - u32 off; + u32 off, max; switch (ptr_reg->type) { case PTR_TO_STACK: + /* Offset 0 is out-of-bounds, but acceptable start for the + * left direction, see BPF_REG_FP. + */ + max = MAX_BPF_STACK + mask_to_left; /* Indirect variable offset stack access is prohibited in * unprivileged mode so it's not handled here. */ @@ -4926,15 +4930,16 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, *ptr_limit = MAX_BPF_STACK + off; else *ptr_limit = -off - 1; - return 0; + return *ptr_limit >= max ? -ERANGE : 0; case PTR_TO_MAP_VALUE: + max = ptr_reg->map_ptr->value_size; if (mask_to_left) { *ptr_limit = ptr_reg->umax_value + ptr_reg->off; } else { off = ptr_reg->smin_value + ptr_reg->off; *ptr_limit = ptr_reg->map_ptr->value_size - off - 1; } - return 0; + return *ptr_limit >= max ? -ERANGE : 0; default: return -EINVAL; }