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libselinux: restorecon: pin file to avoid TOCTOU issues

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Pin the file to operate on in restorecon_sb() to prevent symlink attacks
in between the label database lookup, the current context query and the
final context write.  Also don't use the file information from
fts_read(3), which might also be out of sync.

Due to querying file information twice, one in fts_read(3) needed for
the cross device check and one on the pinned file descriptor for the
database lookup, there is a slight slowdown:

    [current]
    Time (mean ± σ):     14.456 s ±  0.306 s    [User: 45.863 s, System: 4.463 s]
    Range (min … max):   14.275 s … 15.294 s    10 runs

    [changed]
    Time (mean ± σ):     15.843 s ±  0.045 s    [User: 46.274 s, System: 9.495 s]
    Range (min … max):   15.787 s … 15.916 s    10 runs

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Acked-by: James Carter <jwcart2@gmail.com>
This commit is contained in:
Christian Göttsche 2022-05-11 20:42:25 +02:00 committed by James Carter
parent aaa49acac9
commit 7e979b56fd
1 changed files with 25 additions and 18 deletions

43
libselinux/src/selinux_restorecon.c
View File

@ -621,13 +621,13 @@ out:
return rc;
}
static int restorecon_sb(const char *pathname, const struct stat *sb,
struct rest_flags *flags, bool first)
static int restorecon_sb(const char *pathname, struct rest_flags *flags, bool first)
{
char *newcon = NULL;
char *curcon = NULL;
char *newtypecon = NULL;
int rc;
int fd = -1, rc;
struct stat stat_buf;
bool updated = false;
const char *lookup_path = pathname;
float pc;
@ -642,13 +642,21 @@ static int restorecon_sb(const char *pathname, const struct stat *sb,
lookup_path += rootpathlen;
}
fd = open(pathname, O_PATH | O_NOFOLLOW | O_EXCL);
if (fd < 0)
goto err;
rc = fstat(fd, &stat_buf);
if (rc < 0)
goto err;
if (rootpath != NULL && lookup_path[0] == '\0')
/* this is actually the root dir of the alt root. */
rc = selabel_lookup_raw(fc_sehandle, &newcon, "/",
sb->st_mode);
stat_buf.st_mode);
else
rc = selabel_lookup_raw(fc_sehandle, &newcon, lookup_path,
sb->st_mode);
stat_buf.st_mode);
if (rc < 0) {
if (errno == ENOENT) {
@ -657,10 +665,10 @@ static int restorecon_sb(const char *pathname, const struct stat *sb,
"Warning no default label for %s\n",
lookup_path);
return 0; /* no match, but not an error */
goto out; /* no match, but not an error */
}
return -1;
goto err;
}
if (flags->progress) {
@ -680,19 +688,17 @@ static int restorecon_sb(const char *pathname, const struct stat *sb,
}
if (flags->add_assoc) {
rc = filespec_add(sb->st_ino, newcon, pathname, flags);
rc = filespec_add(stat_buf.st_ino, newcon, pathname, flags);
if (rc < 0) {
selinux_log(SELINUX_ERROR,
"filespec_add error: %s\n", pathname);
freecon(newcon);
return -1;
goto out1;
}
if (rc > 0) {
/* Already an association and it took precedence. */
freecon(newcon);
return 0;
goto out;
}
}
@ -700,7 +706,7 @@ static int restorecon_sb(const char *pathname, const struct stat *sb,
selinux_log(SELINUX_INFO, "%s matched by %s\n",
pathname, newcon);
if (lgetfilecon_raw(pathname, &curcon) < 0) {
if (fgetfilecon_raw(fd, &curcon) < 0) {
if (errno != ENODATA)
goto err;
@ -733,7 +739,7 @@ static int restorecon_sb(const char *pathname, const struct stat *sb,
}
if (!flags->nochange) {
if (lsetfilecon(pathname, newcon) < 0)
if (fsetfilecon(fd, newcon) < 0)
goto err;
updated = true;
}
@ -758,6 +764,8 @@ static int restorecon_sb(const char *pathname, const struct stat *sb,
out:
rc = 0;
out1:
if (fd >= 0)
close(fd);
freecon(curcon);
freecon(newcon);
return rc;
@ -855,7 +863,6 @@ static void *selinux_restorecon_thread(void *arg)
FTSENT *ftsent;
int error;
char ent_path[PATH_MAX];
struct stat ent_st;
bool first = false;
if (state->parallel)
@ -953,11 +960,11 @@ loop_body:
/* fall through */
default:
strcpy(ent_path, ftsent->fts_path);
ent_st = *ftsent->fts_statp;
if (state->parallel)
pthread_mutex_unlock(&state->mutex);
error = restorecon_sb(ent_path, &ent_st, &state->flags,
error = restorecon_sb(ent_path, &state->flags,
first);
if (state->parallel) {
@ -1153,7 +1160,7 @@ static int selinux_restorecon_common(const char *pathname_orig,
goto cleanup;
}
error = restorecon_sb(pathname, &sb, &state.flags, true);
error = restorecon_sb(pathname, &state.flags, true);
goto cleanup;
}