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    Subject[PATCH 4.19 082/142] bpf: fix check of allowed specifiers in bpf_trace_printk
    Date
    4.19-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    [ Upstream commit 1efb6ee3edea57f57f9fb05dba8dcb3f7333f61f ]

    A format string consisting of "%p" or "%s" followed by an invalid
    specifier (e.g. "%p%\n" or "%s%") could pass the check which
    would make format_decode (lib/vsprintf.c) to warn.

    Fixes: 9c959c863f82 ("tracing: Allow BPF programs to call bpf_trace_printk()")
    Reported-by: syzbot+1ec5c5ec949c4adaa0c4@syzkaller.appspotmail.com
    Signed-off-by: Martynas Pumputis <m@lambda.lt>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/trace/bpf_trace.c | 8 +++++---
    1 file changed, 5 insertions(+), 3 deletions(-)

    diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
    index 08fcfe440c63..9864a35c8bb5 100644
    --- a/kernel/trace/bpf_trace.c
    +++ b/kernel/trace/bpf_trace.c
    @@ -196,11 +196,13 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
    i++;
    } else if (fmt[i] == 'p' || fmt[i] == 's') {
    mod[fmt_cnt]++;
    - i++;
    - if (!isspace(fmt[i]) && !ispunct(fmt[i]) && fmt[i] != 0)
    + /* disallow any further format extensions */
    + if (fmt[i + 1] != 0 &&
    + !isspace(fmt[i + 1]) &&
    + !ispunct(fmt[i + 1]))
    return -EINVAL;
    fmt_cnt++;
    - if (fmt[i - 1] == 's') {
    + if (fmt[i] == 's') {
    if (str_seen)
    /* allow only one '%s' per fmt string */
    return -EINVAL;
    --
    2.19.1


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