library: Better PID file checks
This started off with fixing the compilier warning: proc/readproc.c: In function ‘simple_nextpid’: proc/readproc.c:1373:38: warning: ‘%s’ directive output may be truncated writing up to 255 bytes into a region of size 58 [-Wformat-truncation=] 1373 | snprintf(path, PROCPATHLEN, "/proc/%s", ent->d_name); | ^~ proc/readproc.c:1373:3: note: ‘snprintf’ output between 7 and 262 bytes into a destination of size 64 1373 | snprintf(path, PROCPATHLEN, "/proc/%s", ent->d_name); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We know that ent->d_name will fit under 64 bytes because we check the name starts with a digit. The first change was simple and changed the printf to use tgid like the task function below it. Is everything under /proc that starts with a digit a directory with a PID only? Today, it is but there are no guarantees. The entire function works ok if every non-pid directory doesn't start with a number. We don't check for strtoul() having an issue nor if the for loop just falls off the end. The moment the kernel guys (or some module writer) think "/proc/12mykernelval" is a neat idea this function is in trouble. We won't get buffer overflow as we are using snprintf at least. This change now: We check if strtoul() actually came across a number Process the pid directory as a conditional branch Treat falling off the for loop as a not-found Signed-off-by: Craig Small <csmall@dropbear.xyz>
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@ -1361,17 +1361,22 @@ next_task:
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// This finds processes in /proc in the traditional way.
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// Return non-zero on success.
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static int simple_nextpid(PROCTAB *restrict const PT, proc_t *restrict const p) {
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static __thread struct dirent *ent; /* dirent handle */
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char *restrict const path = PT->path;
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for (;;) {
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ent = readdir(PT->procfs);
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if(!ent || !ent->d_name[0]) return 0;
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if(*ent->d_name > '0' && *ent->d_name <= '9') break;
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}
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p->tgid = strtoul(ent->d_name, NULL, 10);
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p->tid = p->tgid;
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snprintf(path, PROCPATHLEN, "/proc/%s", ent->d_name);
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return 1;
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static __thread struct dirent *ent; /* dirent handle */
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char *restrict const path = PT->path;
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for (;;) {
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ent = readdir(PT->procfs);
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if (!ent || !ent->d_name[0]) return 0;
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if (*ent->d_name > '0' && *ent->d_name <= '9') {
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errno = 0;
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p->tgid = strtoul(ent->d_name, NULL, 10);
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if (errno == 0) {
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p->tid = p->tgid;
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snprintf(path, PROCPATHLEN, "/proc/%d", p->tgid);
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return 1;
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}
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}
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}
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return 0;
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}
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