The offset must be multiplied by 4 to be sure to access the correct
32bit word in the stack scratch space.
For instance, a store at scratch memory cell #1 was generating the
following:
st r4, [sp, #1]
While the correct code for this is:
st r4, [sp, #4]
To reproduce the bug (assuming your system has a NIC with the mac
address 52:54:00:12:34:56):
echo 0 > /proc/sys/net/core/bpf_jit_enable
tcpdump -ni eth0 "ether[1] + ether[2] - ether[3] * ether[4] - ether[5] \
== -0x3AA" # this will capture packets as expected
echo 1 > /proc/sys/net/core/bpf_jit_enable
tcpdump -ni eth0 "ether[1] + ether[2] - ether[3] * ether[4] - ether[5] \
== -0x3AA" # this will not.
This bug was present since the original inclusion of bpf_jit for ARM
(ddecdfce: ARM: 7259/3: net: JIT compiler for packet filters).
Signed-off-by: Nicolas Schichan <nschichan@freebox.fr>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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