From: Andrei Matei andreimatei1@gmail.com
[ Upstream commit 1d38a9ee81570c4bd61f557832dead4d6f816760 ]
This patch promotes the arithmetic around checking stack bounds to be done in the 64-bit domain, instead of the current 32bit. The arithmetic implies adding together a 64-bit register with a int offset. The register was checked to be below 1<<29 when it was variable, but not when it was fixed. The offset either comes from an instruction (in which case it is 16 bit), from another register (in which case the caller checked it to be below 1<<29 [1]), or from the size of an argument to a kfunc (in which case it can be a u32 [2]). Between the register being inconsistently checked to be below 1<<29, and the offset being up to an u32, it appears that we were open to overflowing the `int`s which were currently used for arithmetic.
[1] https://github.com/torvalds/linux/blob/815fb87b753055df2d9e50f6cd80eb10235fe... [2] https://github.com/torvalds/linux/blob/815fb87b753055df2d9e50f6cd80eb10235fe...
Reported-by: Andrii Nakryiko andrii.nakryiko@gmail.com Signed-off-by: Andrei Matei andreimatei1@gmail.com Signed-off-by: Andrii Nakryiko andrii@kernel.org Acked-by: Andrii Nakryiko andrii@kernel.org Link: https://lore.kernel.org/bpf/20231207041150.229139-4-andreimatei1@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 45c50ee9b037..2ee5f859e024 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3883,7 +3883,7 @@ static int check_ptr_to_map_access(struct bpf_verifier_env *env, * The minimum valid offset is -MAX_BPF_STACK for writes, and * -state->allocated_stack for reads. */ -static int check_stack_slot_within_bounds(int off, +static int check_stack_slot_within_bounds(s64 off, struct bpf_func_state *state, enum bpf_access_type t) { @@ -3912,7 +3912,7 @@ static int check_stack_access_within_bounds( struct bpf_reg_state *regs = cur_regs(env); struct bpf_reg_state *reg = regs + regno; struct bpf_func_state *state = func(env, reg); - int min_off, max_off; + s64 min_off, max_off; int err; char *err_extra;
@@ -3925,7 +3925,7 @@ static int check_stack_access_within_bounds( err_extra = " write to";
if (tnum_is_const(reg->var_off)) { - min_off = reg->var_off.value + off; + min_off = (s64)reg->var_off.value + off; if (access_size > 0) max_off = min_off + access_size - 1; else