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From f3db9bd609494099f0c1b95231c5dfe383346929 Mon Sep 17 00:00:00 2001
From: Karel Zak <kzak@redhat.com>
Date: Wed, 24 Nov 2021 13:53:25 +0100
Subject: [PATCH] libmount: fix UID check for FUSE umount [CVE-2021-3995]
Improper UID check allows an unprivileged user to unmount FUSE
filesystems of users with similar UID.
Signed-off-by: Karel Zak <kzak@redhat.com>
CVE: CVE-2021-3995
Upstream-Status: Backport [https://github.com/util-linux/util-linux/commit/f3db9bd609494099f0c1b95231c5dfe383346929]
Signed-off-by: Ranjitsinh Rathod <ranjitsinh.rathod@kpit.com>
---
include/strutils.h | 2 +-
libmount/src/context_umount.c | 14 +++---------
libmount/src/mountP.h | 1 +
libmount/src/optstr.c | 42 +++++++++++++++++++++++++++++++++++
4 files changed, 47 insertions(+), 12 deletions(-)
diff --git a/include/strutils.h b/include/strutils.h
index 6e95707ea9..a84d29594d 100644
--- a/include/strutils.h
+++ b/include/strutils.h
@@ -91,8 +91,8 @@ static inline char *mem2strcpy(char *dest, const void *src, size_t n, size_t nma
if (n + 1 > nmax)
n = nmax - 1;
+ memset(dest, '\0', nmax);
memcpy(dest, src, n);
- dest[nmax-1] = '\0';
return dest;
}
diff --git a/libmount/src/context_umount.c b/libmount/src/context_umount.c
index 173637a15a..8773c65ffa 100644
--- a/libmount/src/context_umount.c
+++ b/libmount/src/context_umount.c
@@ -393,10 +393,7 @@ static int is_fuse_usermount(struct libmnt_context *cxt, int *errsv)
struct libmnt_ns *ns_old;
const char *type = mnt_fs_get_fstype(cxt->fs);
const char *optstr;
- char *user_id = NULL;
- size_t sz;
- uid_t uid;
- char uidstr[sizeof(stringify_value(ULONG_MAX))];
+ uid_t uid, entry_uid;
*errsv = 0;
@@ -413,11 +410,7 @@ static int is_fuse_usermount(struct libmnt_context *cxt, int *errsv)
optstr = mnt_fs_get_fs_options(cxt->fs);
if (!optstr)
return 0;
-
- if (mnt_optstr_get_option(optstr, "user_id", &user_id, &sz) != 0)
- return 0;
-
- if (sz == 0 || user_id == NULL)
+ if (mnt_optstr_get_uid(optstr, "user_id", &entry_uid) != 0)
return 0;
/* get current user */
@@ -434,8 +427,7 @@ static int is_fuse_usermount(struct libmnt_context *cxt, int *errsv)
return 0;
}
- snprintf(uidstr, sizeof(uidstr), "%lu", (unsigned long) uid);
- return strncmp(user_id, uidstr, sz) == 0;
+ return uid == entry_uid;
}
/*
diff --git a/libmount/src/mountP.h b/libmount/src/mountP.h
index d43a835418..22442ec55e 100644
--- a/libmount/src/mountP.h
+++ b/libmount/src/mountP.h
@@ -400,6 +400,7 @@ extern const struct libmnt_optmap *mnt_optmap_get_entry(
const struct libmnt_optmap **mapent);
/* optstr.c */
+extern int mnt_optstr_get_uid(const char *optstr, const char *name, uid_t *uid);
extern int mnt_optstr_remove_option_at(char **optstr, char *begin, char *end);
extern int mnt_optstr_fix_gid(char **optstr, char *value, size_t valsz, char **next);
extern int mnt_optstr_fix_uid(char **optstr, char *value, size_t valsz, char **next);
diff --git a/libmount/src/optstr.c b/libmount/src/optstr.c
index 921b9318e7..16800f571c 100644
--- a/libmount/src/optstr.c
+++ b/libmount/src/optstr.c
@@ -1090,6 +1090,48 @@ int mnt_optstr_fix_user(char **optstr)
return rc;
}
+/*
+ * Converts value from @optstr addressed by @name to uid.
+ *
+ * Returns: 0 on success, 1 if not found, <0 on error
+ */
+int mnt_optstr_get_uid(const char *optstr, const char *name, uid_t *uid)
+{
+ char *value = NULL;
+ size_t valsz = 0;
+ char buf[sizeof(stringify_value(UINT64_MAX))];
+ int rc;
+ uint64_t num;
+
+ assert(optstr);
+ assert(name);
+ assert(uid);
+
+ rc = mnt_optstr_get_option(optstr, name, &value, &valsz);
+ if (rc != 0)
+ goto fail;
+
+ if (valsz > sizeof(buf) - 1) {
+ rc = -ERANGE;
+ goto fail;
+ }
+ mem2strcpy(buf, value, valsz, sizeof(buf));
+
+ rc = ul_strtou64(buf, &num, 10);
+ if (rc != 0)
+ goto fail;
+ if (num > ULONG_MAX || (uid_t) num != num) {
+ rc = -ERANGE;
+ goto fail;
+ }
+ *uid = (uid_t) num;
+
+ return 0;
+fail:
+ DBG(UTILS, ul_debug("failed to convert '%s'= to number [rc=%d]", name, rc));
+ return rc;
+}
+
/**
* mnt_match_options:
* @optstr: options string
|
