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authorYonghong Song <yhs@fb.com>2018-07-30 08:49:03 -0700
committerDaniel Borkmann <daniel@iogearbox.net>2018-07-31 00:37:09 +0200
commit573b3aa6940661dc50c383213d428c27df78be7c (patch)
treed43b1d082e751d2e50b6ceee69228f1dee599daf /net
parentnetlink: Don't shift with UB on nlk->ngroups (diff)
tools/bpftool: fix a percpu_array map dump problem
I hit the following problem when I tried to use bpftool to dump a percpu array. $ sudo ./bpftool map show 61: percpu_array name stub flags 0x0 key 4B value 4B max_entries 1 memlock 4096B ... $ sudo ./bpftool map dump id 61 bpftool: malloc.c:2406: sysmalloc: Assertion `(old_top == initial_top (av) && old_size == 0) || \ ((unsigned long) (old_size) >= MINSIZE && \ prev_inuse (old_top) && \ ((unsigned long) old_end & (pagesize - 1)) == 0)' failed. Aborted Further debugging revealed that this is due to miscommunication between bpftool and kernel. For example, for the above percpu_array with value size of 4B. The map info returned to user space has value size of 4B. In bpftool, the values array for lookup is allocated like: info->value_size * get_possible_cpus() = 4 * get_possible_cpus() In kernel (kernel/bpf/syscall.c), the values array size is rounded up to multiple of 8. round_up(map->value_size, 8) * num_possible_cpus() = 8 * num_possible_cpus() So when kernel copies the values to user buffer, the kernel will overwrite beyond user buffer boundary. This patch fixed the issue by allocating and stepping through percpu map value array properly in bpftool. Fixes: 71bb428fe2c19 ("tools: bpf: add bpftool") Signed-off-by: Yonghong Song <yhs@fb.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Diffstat (limited to 'net')
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