tree 4d0ef813eb4f1e59d8d69da7d9ee6dbe9e5e7afd
parent 629dfc2cb53984b5d267da6ed6480b64bec7500f
author Florent Revest <revest@chromium.org> 1620720654 +0200
committer Oleksandr Tymoshenko <ovt@google.com> 1649382603 +0000

UPSTREAM: bpf: Fix nested bpf_bprintf_prepare with more per-cpu buffers

The bpf_seq_printf, bpf_trace_printk and bpf_snprintf helpers share one
per-cpu buffer that they use to store temporary data (arguments to
bprintf). They "get" that buffer with try_get_fmt_tmp_buf and "put" it
by the end of their scope with bpf_bprintf_cleanup.

If one of these helpers gets called within the scope of one of these
helpers, for example: a first bpf program gets called, uses
bpf_trace_printk which calls raw_spin_lock_irqsave which is traced by
another bpf program that calls bpf_snprintf, then the second "get"
fails. Essentially, these helpers are not re-entrant. They would return
-EBUSY and print a warning message once.

This patch triples the number of bprintf buffers to allow three levels
of nesting. This is very similar to what was done for tracepoints in
"9594dc3c7e7 bpf: fix nested bpf tracepoints with per-cpu data"

Fixes: d9c9e4db186a ("bpf: Factorize bpf_trace_printk and bpf_seq_printf")
Reported-by: syzbot+63122d0bc347f18c1884@syzkaller.appspotmail.com
Signed-off-by: Florent Revest <revest@chromium.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210511081054.2125874-1-revest@chromium.org
(cherry picked from commit e2d5b2bb769fa5f500760caba76436ba3a10a895)
Signed-off-by: Brendan Jackman <jackmanb@google.com>

SOURCE=UPSTREAM(e2d5b2bb769fa5f500760caba76436ba3a10a895)
BUG=b:217368493

Change-Id: Icfdcaeb3239ab365b2b4d0e8f17d18b131d88a41