Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH] perf event-parse: Use fixed size string for comms | Date | Thu, 30 Aug 2018 15:28:18 +0000 |
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From: cphlipot0@gmail.com > Sent: 30 August 2018 03:20 > > Some implementations of libc do not support the 'm' width modifier > as part of the scanf string format specifier. This can cause the > parsing to fail. Since the parser never checks if the scanf > parsing was successesful, this can result in a crash. > > Change the comm string to be allocated as a fixed size instead of > dynamically using 'm' scanf width modifier. This can be safely done > since comm size is limited to 16 bytes by TASK_COMM_LEN within the > kernel. > > This change prevents perf from crashing when linked against bionic > as well as reduces the total number of heap allocations and frees > invoked while accomplishing the same task. > > Signed-off-by: Chris Phlipot <cphlipot0@gmail.com> > --- > tools/perf/util/trace-event-parse.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/tools/perf/util/trace-event-parse.c b/tools/perf/util/trace-event-parse.c > index 920b1d58a068..e76214f8d596 100644 > --- a/tools/perf/util/trace-event-parse.c > +++ b/tools/perf/util/trace-event-parse.c > @@ -164,16 +164,15 @@ void parse_ftrace_printk(struct tep_handle *pevent, > void parse_saved_cmdline(struct tep_handle *pevent, > char *file, unsigned int size __maybe_unused) > { > - char *comm; > + char comm[17]; /* Max comm length in the kernel is 16. */ > char *line; > char *next = NULL; > int pid; > > line = strtok_r(file, "\n", &next); > while (line) { > - sscanf(line, "%d %ms", &pid, &comm); > - tep_register_comm(pevent, comm, pid); > - free(comm); > + if (sscanf(line, "%d %16s", &pid, comm) == 2) > + tep_register_comm(pevent, comm, pid); > line = strtok_r(NULL, "\n", &next);
Seems to me that sscanf is the wrong tool for the job (as usual). Why not just: pid = strtoul(line, &comm, 10); while (*comm == ' ') comm++; tep_register_comm(pevent, comm, pid);
David
- Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
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