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bpf: fix check of allowed specifiers in bpf_trace_printk

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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: 9c959c863f ("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>
This commit is contained in:
Martynas Pumputis 2018-11-23 17:43:26 +01:00 committed by Daniel Borkmann
parent 813961de3e
commit 1efb6ee3ed
1 changed files with 5 additions and 3 deletions
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8
kernel/trace/bpf_trace.c
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@ -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;