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fix: improve file checks for procfs knobs

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CodeQL checks flagged this pattern as a TOCTOU race.

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>
This commit is contained in:
Robin H. Johnson
2025-01-02 09:54:32 -08:00
parent f60e47c4c4
commit 133fed4b26
1 changed files with 27 additions and 13 deletions
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40
privsep-linux.c
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@@ -180,30 +180,44 @@ static int set_interface_var(const char *iface, const char *var, const char *nam
int retval = -1;
FILE *fp = 0;
char *spath = strdupf(var, iface);
int fd = -1 ;
/* No path traversal */
// TODO: if interface names contain '/' in future, this may break.
if (!iface[0] || !strcmp(iface, ".") || !strcmp(iface, "..") || strchr(iface, '/'))
goto cleanup;
goto errmsg;
if (access(spath, F_OK) != 0)
goto cleanup;
fp = fopen(spath, "w");
if (!fp) {
if (name)
flog(LOG_ERR, "failed to set %s (%u) for %s: %s", name, val, iface, strerror(errno));
goto cleanup;
// Open the file for writing, ONLY if it already exists.
// explicitly ensure that O_CREAT is *NOT* set.
fd = open(spath, O_WRONLY & (~O_CREAT), 0);
if (fd == -1) {
// If the file does NOT exist, this is non-fatal; as we fallback to a
// different filename at a higher level.
// ensure we cleanup and return -1 to the higher level
if (errno == ENOENT)
goto cleanup;
// If we got some other error, e.g. ENOACCESS
goto errmsg;
}
if (0 > fprintf(fp, "%u", val)) {
goto cleanup;
// We know the file exists now, write to it.
fp = fdopen(fd, "w");
if (!fp)
goto errmsg;
if (fprintf(fp, "%u", val) > 0) {
retval = 0;
}
retval = 0;
errmsg:
if (name && retval != 0)
flog(LOG_ERR, "failed to set %s (%u) for %s: %s", name, val, iface, strerror(errno));
cleanup:
if (fp)
fclose(fp);
if (fd != -1)
close(fd);
free(spath);