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ucm: fix TOCTOU race condition #367

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ucm: fix TOCTOU race condition #367

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30 changes: 16 additions & 14 deletions src/ucm/ucm_subs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -518,30 +518,32 @@ static char *rval_sysfs(snd_use_case_mgr_t *uc_mgr ATTRIBUTE_UNUSED, const char
if (id[0] == '/')
id++;
snprintf(path, sizeof(path), "%s/%s", e, id);
if (lstat64(path, &sb) != 0)
return NULL;
if (S_ISLNK(sb.st_mode)) {
len = readlink(path, link, sizeof(link) - 1);
if (len <= 0) {
uc_error("sysfs: cannot read link '%s' (%d)", path, errno);
return NULL;
}
len = readlink(path, link, sizeof(link) - 1);
if (len > 0) {
link[len] = '\0';
e = strrchr(link, '/');
if (e)
return strdup(e + 1);
return NULL;
}
if (S_ISDIR(sb.st_mode))
return NULL;
if ((sb.st_mode & S_IRUSR) == 0)
return NULL;

fd = open(path, O_RDONLY);
fd = open(path, O_RDONLY | O_NOFOLLOW);
if (fd < 0) {
uc_error("sysfs open failed for '%s' (%d)", path, errno);
return NULL;
}
if (fstat64(fd, &sb) != 0) {
close(fd);
return NULL;
}
if (S_ISDIR(sb.st_mode)) {
close(fd);
return NULL;
}
if ((sb.st_mode & S_IRUSR) == 0) {
close(fd);
return NULL;
}

len = read(fd, path, sizeof(path)-1);
close(fd);
if (len < 0) {
Expand Down