segfault when given logfile name is already taken by a directory

[honggyukim]

Here is an example recording a simple program.

$ gcc -pg tests/s-abc.c -o t-abc

$ uftrace record t-abc

$ uftrace replay
# DURATION     TID     FUNCTION
   1.700 us [ 16855] | __monstartup();
   1.300 us [ 16855] | __cxa_atexit();
            [ 16855] | main() {
            [ 16855] |   a() {
            [ 16855] |     b() {
            [ 16855] |       c() {
   1.400 us [ 16855] |         getpid();
   3.600 us [ 16855] |       } /* c */
   5.600 us [ 16855] |     } /* b */
   7.300 us [ 16855] |   } /* a */
   9.200 us [ 16855] | } /* main */

The above example works fine and the debug message can be stored with --logfile option as follows:

$ uftrace record -v --logfile=dir t-abc

However, it gets crashed if the given file name is already used by another directory as follows:

$ mkdir dir

$ uftrace record -v --logfile=dir t-abc
Segmentation fault (core dumped)

It needs to check if the file is already exists or not.

[honggyukim]

The crash point is in uftrace.c file as follows:

1042│ int main(int argc, char *argv[])
1043│ {
        ...
1080│         if (dbg_domain_set && !debug)
1081│                 debug = 1;
1082│
1083│         if (opts.logfile) {
1084│                 logfp = fopen(opts.logfile, "a");
1085│                 if (logfp == NULL)
1086├───────────────────────> pr_err("cannot open log file");
1087│
1088│                 setvbuf(logfp, NULL, _IOLBF, 1024);
1089│         }
1090│         else if (debug) {
1091│                 /* ensure normal output is not mixed by debug message */
1092│                 setvbuf(outfp, NULL, _IOLBF, 1024);
1093│         }
        ...

[honggyukim]

This is a simple bug so anyone can fix this if interested.

[rls1004]

Can i take this issue?

[honggyukim]

Sure, please take it. I would like to provide more info regarding this.

Please refer to the following discussion.

• record: Send logfile for -H/--host option #707 (comment)
• logfile enhancement #831

I think we better have some protection code for this.

[rls1004]

The problem seems to be caused by writing an error message to logfd when logfd is NULL.
Before calling pr_err(), I want to set logfd to stderr.
Is this okay?

[honggyukim]

I'm okay with it. Thanks!