From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793210008; b=ixP882+UTI9adQvn0sDIkuDIFi1baYXJh5XL+fATqmBLI783tmwavQQvCvIWx6jH2ik8 +9ZM+DLefFHSiQILMhlrRY+pSQnFxQIHZncDfl2ATvN/NfG8cAKyQKmIzZbAf3GLh4oH0 1O5vs0LY3UpFE318rPffiDcRKU6hQHjWgv8+FsZ1fgOArc9fmyUWHvdFm42EKYVjhEf/Q 1/rQxZpbYz/poX2NTkxn/UwbxZUFNr9ewmL3FJRYBWtiaAhql5tRlpDLdZDKaycWuNXIh MNJ8Mfx+2EKqVv5XsjkAp/nry5iaWbCLW304z4xw/Fj8KNA1hIr1FFcCOUYS7IuJvVg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793210008; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=Gbno2xsMupQj/uCDtB0ldgd7sjwzoTwTL9A4mWn6HXk=; b=FNuCcbO3C6hv3n5IfkMbORzOpDRceDp63pLkK3l90KsJe/2jYCS5AqPnjoNJwGY/mTNA SbbL0gsh0OuNEX5qU2jnlnaFxKQ2MbIQk8YE4lhMwAiNrSDIEI70RRD0S47TW+axEYAkv BUhxy/bF6I5Lh0VS2rpUZ6hSQm3pmY6irCe7lhzAczg+nhAfkPkxefTuJX7erfuBTNRX7 Tavb6vsnnRbfJVW8zF62pt2OPqXtuEKkBOkWVZta8fg4ZXyxJCT6lreZ79SPCh4s2ftu7 64pd05ZdUUcuyIQ58gq/2eeXXN2yiXWUgkJnwzonAnaDYP1a2P+rVwtFMB7pVwUlpwA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=RfA6Iui2; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4F1DC606A31A; Wed, 28 Oct 2026 17:53:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=RfA6Iui2 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9D1E01F01825; Wed, 28 Oct 2026 17:53:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793210008; bh=Gbno2xsMupQj/uCDtB0ldgd7sjwzoTwTL9A4mWn6HXk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=RfA6Iui2usRMcwgMYCaOfJppLzKZpds0iu6xND5UgoBphVVSdCcfYyAsBuleyw+m+ qmXgiKkqWmnataFllkacsITe8inti96c/Ii24Lhj5vUa07PfdQvERkwG+W8GpjxneD 7B1hL2uvm4rSvAKNX3NfFgqp3vmPVk5FuE6oMPT8= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Christian Brauner (Amutable)" Subject: [PATCH 6.6 042/168] unicode: free the map after a grace period Date: Wed, 28 Oct 2026 17:59:38 +0100 Message-ID: <20261028165944.086696010@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028165943.089486480@linuxfoundation.org> References: <20261028165943.089486480@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Christian Brauner commit a96c5299bd7305eb984377681eb3222a57376405 upstream. generic_ci_d_hash() and generic_ci_d_compare() read sb->s_encoding and dereference the unicode map while a pathwalk in rcu mode holds nothing but rcu_read_lock(). The filesystems that use them, ext4, f2fs and tmpfs, drop the map with utf8_unload() from ->put_super(), which runs when the last reference to the mount goes away. A lookup that is still inside such a filesystem at that point reads a freed map. With a pathwalk held up in utf8_casefold_hash() while the last reference to a casefolded tmpfs goes away: BUG: KASAN: slab-use-after-free in utf8nlookup+0x74c/0x950 Read of size 8 at addr ff110001030fe658 by task walker/98 Call Trace: utf8nlookup+0x74c/0x950 utf8byte+0x160/0x1560 utf8_casefold_hash+0x167/0x230 generic_ci_d_hash+0xdd/0x1c0 link_path_walk+0x11ad/0x1d30 path_lookupat+0x63/0xb00 filename_lookup+0x1f1/0x5b0 vfs_statx+0xd7/0x3b0 [...] Allocated by task 94: __kmalloc_cache_noprof+0x249/0x560 utf8_load+0x4e/0x570 shmem_parse_opt_casefold.isra.0+0x92/0x270 [...] Freed by task 97: kfree+0x1db/0x5b0 shmem_put_super+0x72/0x170 generic_shutdown_super+0x14c/0x530 kill_anon_super+0x3a/0x60 deactivate_locked_super+0x9c/0xf0 cleanup_mnt+0x9f/0x130 So far that has been hard to hit. umount(2) waits for a grace period in namespace_unlock() before it drops the mount, so only a mount whose last reference goes away elsewhere, like the close of a file or a chdir out of a lazily unmounted directory, can race a walker. So it is reachable. Delay the free until a grace period has passed. The map and the data table it holds a reference to then outlive any pathwalk that found the superblock before the mount went away. The reference on the data table module is dropped from the rcu callback as well. utf8-core is built in whenever CONFIG_UNICODE is set, so there is no module exit that would have to wait for the callbacks. Overlayfs points the s_encoding of an overlay at the map of its first layer without taking a reference of its own. That stays correct. The layer is held by the overlay, so its map is dropped only after the overlay is gone. Fixes: b886ee3e778e ("ext4: Support case-insensitive file name lookups") Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20261009-work-fixes-rcu-v1-6-7446d2d335e6@kernel.org Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Greg Kroah-Hartman --- fs/unicode/utf8-core.c | 21 +++++++++++++++++---- include/linux/unicode.h | 1 + 2 files changed, 18 insertions(+), 4 deletions(-) --- a/fs/unicode/utf8-core.c +++ b/fs/unicode/utf8-core.c @@ -3,6 +3,7 @@ #include #include #include +#include #include #include #include @@ -205,12 +206,24 @@ out_free_um: } EXPORT_SYMBOL(utf8_load); +static void utf8_unload_rcu(struct rcu_head *head) +{ + struct unicode_map *um = container_of(head, struct unicode_map, rcu); + + symbol_put(utf8_data_table); + kfree(um); +} + +/* + * A pathwalk in rcu mode may still be in ->d_hash() or ->d_compare() of a + * filesystem that is being torn down and read the map through its + * superblock, so the map and the tables it points to have to outlive the + * grace period. + */ void utf8_unload(struct unicode_map *um) { - if (um) { - symbol_put(utf8_data_table); - kfree(um); - } + if (um) + call_rcu(&um->rcu, utf8_unload_rcu); } EXPORT_SYMBOL(utf8_unload); --- a/include/linux/unicode.h +++ b/include/linux/unicode.h @@ -51,6 +51,7 @@ struct unicode_map { unsigned int version; const struct utf8data *ntab[UTF8_NMAX]; const struct utf8data_table *tables; + struct rcu_head rcu; }; int utf8_validate(const struct unicode_map *um, const struct qstr *str);