Overview
About vulnerability
In the Linux kernel, the following vulnerability has been resolved:
bpf: Reject %p% format string in bprintf-like helpers
static const char fmt[] = “%p%”; bpf_trace_printk(fmt, sizeof(fmt));
The above BPF program isn’t rejected and causes a kernel warning at runtime:
Please remove unsupported %\x00 in format string WARNING: CPU: 1 PID: 7244 at lib/vsprintf.c:2680 format_decode+0x49c/0x5d0
This happens because bpf_bprintf_prepare skips over the second %, detected as punctuation, while processing %p. This patch fixes it by not skipping over punctuation. %\x00 is then processed in the next iteration and rejected.
Details
- Affected product:
- AlmaLinux 9.2 ESU , TuxCare 9.6 ESU , Ubuntu 20.04 ELS
- Affected packages:
- linux @ 5.4.0 (+2 more)
In the Linux kernel, the following vulnerability has been resolved:
bpf: Reject %p% format string in bprintf-like helpers
static const char fmt[] = “%p%”; bpf_trace_printk(fmt, sizeof(fmt));
The above BPF program isn’t rejected and causes a kernel warning at runtime:
Please remove unsupported %\x00 in format string WARNING: CPU: 1 PID: 7244 at lib/vsprintf.c:2680 format_decode+0x49c/0x5d0
This happens because bpf_bprintf_prepare skips over the second %, detected as punctuation, while processing %p. This patch fixes it by not skipping over punctuation. %\x00 is then processed in the next iteration and rejected.