Commit 38ca93060163 ("bpf, arm32: save 4 bytes of unneeded stack space") messed up STACK_VAR() by 4 bytes presuming it was related to skb scratch buffer space, but it clearly isn't as this refers to the top word in stack, therefore restore it. This fixes a NULL pointer dereference seen during bootup when JIT is enabled and BPF program run in sk_filter_trim_cap() triggered by systemd-udevd.

JIT rework in 1c35ba122d4a ("ARM: net: bpf: use negative numbers for stacked registers") and 96cced4e774a ("ARM: net: bpf: access eBPF scratch space using ARM FP register") removed the affected parts, so only needed in 4.18 stable.

Fixes: 38ca93060163 ("bpf, arm32: save 4 bytes of unneeded stack space") Reported-by: Peter Robinson pbrobinson@gmail.com Reported-by: Marc Haber mh+netdev@zugschlus.de Tested-by: Stefan Wahren stefan.wahren@i2se.com Tested-by: Peter Robinson pbrobinson@gmail.com Cc: Russell King rmk+kernel@armlinux.org.uk Cc: Alexei Starovoitov ast@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net --- arch/arm/net/bpf_jit_32.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c index f6a62ae..c864f6b 100644 --- a/arch/arm/net/bpf_jit_32.c +++ b/arch/arm/net/bpf_jit_32.c @@ -238,7 +238,7 @@ static void jit_fill_hole(void *area, unsigned int size) #define STACK_SIZE ALIGN(_STACK_SIZE, STACK_ALIGNMENT)

/* Get the offset of eBPF REGISTERs stored on scratch space. */ -#define STACK_VAR(off) (STACK_SIZE - off) +#define STACK_VAR(off) (STACK_SIZE - off - 4)

#if __LINUX_ARM_ARCH__ < 7