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authorAlexei Starovoitov <ast@plumgrid.com>2015-08-28 15:56:23 -0700
committerDavid S. Miller <davem@davemloft.net>2015-08-28 16:27:27 -0700
commit8d3b7dce8622919da5c5822ef7338d6604c9fe6e (patch)
tree8934c8b0f6aac4a01488c59c45b8dc55c64cc721 /kernel/trace
parent1a6877b9c0c2ad901d4335d909432d3bb6d3a330 (diff)
downloadlinux-8d3b7dce8622919da5c5822ef7338d6604c9fe6e.tar.bz2
bpf: add support for %s specifier to bpf_trace_printk()
%s specifier makes bpf program and kernel debugging easier. To make sure that trace_printk won't crash the unsafe string is copied into stack and unsafe pointer is substituted. The following C program: #include <linux/fs.h> int foo(struct pt_regs *ctx, struct filename *filename) { void *name = 0; bpf_probe_read(&name, sizeof(name), &filename->name); bpf_trace_printk("executed %s\n", name); return 0; } when attached to kprobe do_execve() will produce output in /sys/kernel/debug/tracing/trace_pipe : make-13492 [002] d..1 3250.997277: : executed /bin/sh sh-13493 [004] d..1 3250.998716: : executed /usr/bin/gcc gcc-13494 [002] d..1 3250.999822: : executed /usr/lib/gcc/x86_64-linux-gnu/4.7/cc1 gcc-13495 [002] d..1 3251.006731: : executed /usr/bin/as gcc-13496 [002] d..1 3251.011831: : executed /usr/lib/gcc/x86_64-linux-gnu/4.7/collect2 collect2-13497 [000] d..1 3251.012941: : executed /usr/bin/ld Suggested-by: Brendan Gregg <brendan.d.gregg@gmail.com> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'kernel/trace')
-rw-r--r--kernel/trace/bpf_trace.c32
1 files changed, 30 insertions, 2 deletions
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index ef9936df1b04..0fe96c7c8803 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -81,13 +81,16 @@ static const struct bpf_func_proto bpf_probe_read_proto = {
/*
* limited trace_printk()
- * only %d %u %x %ld %lu %lx %lld %llu %llx %p conversion specifiers allowed
+ * only %d %u %x %ld %lu %lx %lld %llu %llx %p %s conversion specifiers allowed
*/
static u64 bpf_trace_printk(u64 r1, u64 fmt_size, u64 r3, u64 r4, u64 r5)
{
char *fmt = (char *) (long) r1;
+ bool str_seen = false;
int mod[3] = {};
int fmt_cnt = 0;
+ u64 unsafe_addr;
+ char buf[64];
int i;
/*
@@ -114,12 +117,37 @@ static u64 bpf_trace_printk(u64 r1, u64 fmt_size, u64 r3, u64 r4, u64 r5)
if (fmt[i] == 'l') {
mod[fmt_cnt]++;
i++;
- } else if (fmt[i] == 'p') {
+ } else if (fmt[i] == 'p' || fmt[i] == 's') {
mod[fmt_cnt]++;
i++;
if (!isspace(fmt[i]) && !ispunct(fmt[i]) && fmt[i] != 0)
return -EINVAL;
fmt_cnt++;
+ if (fmt[i - 1] == 's') {
+ if (str_seen)
+ /* allow only one '%s' per fmt string */
+ return -EINVAL;
+ str_seen = true;
+
+ switch (fmt_cnt) {
+ case 1:
+ unsafe_addr = r3;
+ r3 = (long) buf;
+ break;
+ case 2:
+ unsafe_addr = r4;
+ r4 = (long) buf;
+ break;
+ case 3:
+ unsafe_addr = r5;
+ r5 = (long) buf;
+ break;
+ }
+ buf[0] = 0;
+ strncpy_from_unsafe(buf,
+ (void *) (long) unsafe_addr,
+ sizeof(buf));
+ }
continue;
}