6.6-stable review patch. If anyone has any objections, please let me know.
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From: Dimitar Kanaliev dimitar.kanaliev@siteground.com
[ Upstream commit ae67b9fb8c4e981e929a665dcaa070f4b05ebdb4 ]
coerce_reg_to_size_sx() updates the register state after a sign-extension operation. However, there's a bug in the assignment order of the unsigned min/max values, leading to incorrect truncation:
0: (85) call bpf_get_prandom_u32#7 ; R0_w=scalar() 1: (57) r0 &= 1 ; R0_w=scalar(smin=smin32=0,smax=umax=smax32=umax32=1,var_off=(0x0; 0x1)) 2: (07) r0 += 254 ; R0_w=scalar(smin=umin=smin32=umin32=254,smax=umax=smax32=umax32=255,var_off=(0xfe; 0x1)) 3: (bf) r0 = (s8)r0 ; R0_w=scalar(smin=smin32=-2,smax=smax32=-1,umin=umin32=0xfffffffe,umax=0xffffffff,var_off=(0xfffffffffffffffe; 0x1))
In the current implementation, the unsigned 32-bit min/max values (u32_min_value and u32_max_value) are assigned directly from the 64-bit signed min/max values (s64_min and s64_max):
reg->umin_value = reg->u32_min_value = s64_min; reg->umax_value = reg->u32_max_value = s64_max;
Due to the chain assigmnent, this is equivalent to:
reg->u32_min_value = s64_min; // Unintended truncation reg->umin_value = reg->u32_min_value; reg->u32_max_value = s64_max; // Unintended truncation reg->umax_value = reg->u32_max_value;
Fixes: 1f9a1ea821ff ("bpf: Support new sign-extension load insns") Reported-by: Shung-Hsi Yu shung-hsi.yu@suse.com Reported-by: Zac Ecob zacecob@protonmail.com Signed-off-by: Dimitar Kanaliev dimitar.kanaliev@siteground.com Acked-by: Yonghong Song yonghong.song@linux.dev Reviewed-by: Shung-Hsi Yu shung-hsi.yu@suse.com Link: https://lore.kernel.org/r/20241014121155.92887-2-dimitar.kanaliev@siteground... Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d1050479cbb33..28b09ca5525f0 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6143,10 +6143,10 @@ static void coerce_reg_to_size_sx(struct bpf_reg_state *reg, int size)
/* both of s64_max/s64_min positive or negative */ if ((s64_max >= 0) == (s64_min >= 0)) { - reg->smin_value = reg->s32_min_value = s64_min; - reg->smax_value = reg->s32_max_value = s64_max; - reg->umin_value = reg->u32_min_value = s64_min; - reg->umax_value = reg->u32_max_value = s64_max; + reg->s32_min_value = reg->smin_value = s64_min; + reg->s32_max_value = reg->smax_value = s64_max; + reg->u32_min_value = reg->umin_value = s64_min; + reg->u32_max_value = reg->umax_value = s64_max; reg->var_off = tnum_range(s64_min, s64_max); return; }