From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A9C1917A30A; Sat, 12 Sep 2026 13:51:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789221096; cv=none; b=kfOIps/yo22TOHULFLwfU05yKPMFoIAKzprPYZ9Dl5mHl0y1HsL6CT08SoxiqHWuMQjECdWGSPw2tGvC/FjrVJTv6CDvgbIS0v8/EMFG3mXZcDIKG3MTBiDxtzlROXpG+UbWih+0w7xl2JkGOXI5NPtw9EY79LXyVtvKE2+GGAA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789221096; c=relaxed/simple; bh=tEXoziZFhqC5FRnizWd5qNNmGMzhouAJykNnjWaCUp4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=udj/EckU1vvJKgIvdezItdlaCQXK0fSOyP4oQ5RQNqDvhAcLu1M1LBnxKb1rLsJWFId9CweSEHBvX+G9xearTv+ovOSTfI1/hGH13oBkD8vFWr5DUGiClLTWdfFyjSHccobucUWQPBCFEmK0Nfvmcc+e+7DITeWO86Sj6Mfnv+8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Zt2R9W9V; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Zt2R9W9V" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 304EE1F000FF; Sat, 12 Sep 2026 13:51:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789221095; bh=83a9g64OZF0Ygth4xr0f5m3Fsc3JCJ3tRshaeOFAquQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Zt2R9W9VbP9UXJ0xHWgg4M2hj188O1KUn0FplxZlDAXmu8ymvBSBVIRn9PcEgCXvn gUddc73b2vN4wfGlzq05o4FtJ7NzcYYjqbNpbkX6V3TDpTRSlGTKPhsqDxzZ2gPUal 6rlwFqvRmhuMRYVolvYUH1/cOxVCc3Te2PyroSBw= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jan Kara , Amir Goldstein , Youngjae Kwon , Sasha Levin Subject: [PATCH 6.6 0314/1424] fsnotify: Fix stale object mask after concurrent mark updates Date: Sat, 12 Sep 2026 08:45:46 +0200 Message-ID: <20260912065614.316350966@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065607.279695368@linuxfoundation.org> References: <20260912065607.279695368@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Youngjae Kwon [ Upstream commit e422777fdd4746de1109575c51e65038d4c5c1be ] When a mark gets a new event bit, fanotify and inotify may avoid recalculating the object mask if the cached aggregate already contains that bit. This is racy with a recalculation triggered by a concurrent update to another mark on the same connector. The concurrent scan can read the mark before the new bit is added, while the updater reads the old aggregate before that scan publishes its result. The updater then skips recalculation and the scan publishes a mask without the bit, leaving the object mask stale after both updates complete. This can be reproduced with two fanotify groups watching the same inode: one thread removes FAN_MODIFY from one existing mark while another thread adds FAN_MODIFY to the other mark. After both fanotify_mark() calls return, writes can fail to produce FAN_MODIFY for the group whose mark now contains the bit. This was reproduced on an unmodified v6.12.95 kernel. The equivalent inotify interleaving loses IN_MODIFY events. For normal fanotify additions, recalculate whenever the raw mark mask changes. The normal mask is not cleared asynchronously, so an unchanged addition cannot introduce missing interest. Always recalculate ignore-mask updates because FS_MODIFY handling may clear the ignore mask without taking mark->lock, making snapshot comparisons unreliable. Always recalculate after updating an existing inotify watch. Its replace path temporarily sets mark->mask to zero, so a concurrent scan can observe zero even when the old and final masks are equal. Assigning the replacement mask directly would avoid the transient zero, but existing-watch updates are infrequent, so unconditional recalculation is simpler. Link: https://lore.kernel.org/all/CACwKKmCZdiZDoFuYm6LZhQ=XvHPk0fNKH=X3LmoXMqakYqJaNw@mail.gmail.com/ Fixes: 63c882a05416 ("inotify: reimplement inotify using fsnotify") Fixes: 912ee3946c5e ("fanotify: do not call fanotify_update_object_mask in fanotify_add_mark") Cc: stable@vger.kernel.org # needs adjustments for <= 7.0 Suggested-by: Jan Kara Suggested-by: Amir Goldstein Signed-off-by: Youngjae Kwon Link: https://patch.msgid.link/20260802015801.2426818-1-yjkwon0026@snu.ac.kr Signed-off-by: Jan Kara (cherry picked from commit e422777fdd4746de1109575c51e65038d4c5c1be) [yjkwon0026: Resolve the inotify conflict by retaining the branch-native inode->i_fsnotify_marks argument to fsnotify_recalc_mask(). This tree lacks 35ceae44742e ("fsnotify: Avoid data race between fsnotify_recalc_mask() and fsnotify_object_watched()") and 4520b96b8136 ("fsnotify: inotify: pass mark connector to fsnotify_recalc_mask()"). The differing READ_ONCE() line and connector call are in the conditional deleted by this patch, so neither commit is a prerequisite for this fix.] Signed-off-by: Youngjae Kwon Signed-off-by: Sasha Levin --- fs/notify/fanotify/fanotify_user.c | 12 +++++++----- fs/notify/inotify/inotify_user.c | 15 +-------------- 2 files changed, 8 insertions(+), 19 deletions(-) diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c index f4798d613dc22..763ca835d8fd5 100644 --- a/fs/notify/fanotify/fanotify_user.c +++ b/fs/notify/fanotify/fanotify_user.c @@ -1186,16 +1186,18 @@ static bool fanotify_mark_update_flags(struct fsnotify_mark *fsn_mark, static bool fanotify_mark_add_to_mask(struct fsnotify_mark *fsn_mark, __u32 mask, unsigned int fan_flags) { + __u32 old_mask; bool recalc; spin_lock(&fsn_mark->lock); - if (!(fan_flags & FANOTIFY_MARK_IGNORE_BITS)) + if (!(fan_flags & FANOTIFY_MARK_IGNORE_BITS)) { + old_mask = fsn_mark->mask; fsn_mark->mask |= mask; - else + recalc = old_mask != fsn_mark->mask; + } else { fsn_mark->ignore_mask |= mask; - - recalc = fsnotify_calc_mask(fsn_mark) & - ~fsnotify_conn_mask(fsn_mark->connector); + recalc = true; + } recalc |= fanotify_mark_update_flags(fsn_mark, fan_flags); spin_unlock(&fsn_mark->lock); diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c index 804af9d6078b0..b2c75477f5497 100644 --- a/fs/notify/inotify/inotify_user.c +++ b/fs/notify/inotify/inotify_user.c @@ -540,7 +540,6 @@ static int inotify_update_existing_watch(struct fsnotify_group *group, { struct fsnotify_mark *fsn_mark; struct inotify_inode_mark *i_mark; - __u32 old_mask, new_mask; int replace = !(arg & IN_MASK_ADD); int create = (arg & IN_MASK_CREATE); int ret; @@ -556,27 +555,15 @@ static int inotify_update_existing_watch(struct fsnotify_group *group, i_mark = container_of(fsn_mark, struct inotify_inode_mark, fsn_mark); spin_lock(&fsn_mark->lock); - old_mask = fsn_mark->mask; if (replace) { fsn_mark->mask = 0; fsn_mark->flags &= ~INOTIFY_MARK_FLAGS; } fsn_mark->mask |= inotify_arg_to_mask(inode, arg); fsn_mark->flags |= inotify_arg_to_flags(arg); - new_mask = fsn_mark->mask; spin_unlock(&fsn_mark->lock); - if (old_mask != new_mask) { - /* more bits in old than in new? */ - int dropped = (old_mask & ~new_mask); - /* more bits in this fsn_mark than the inode's mask? */ - int do_inode = (new_mask & ~inode->i_fsnotify_mask); - - /* update the inode with this new fsn_mark */ - if (dropped || do_inode) - fsnotify_recalc_mask(inode->i_fsnotify_marks); - - } + fsnotify_recalc_mask(inode->i_fsnotify_marks); /* return the wd */ ret = i_mark->wd; -- 2.53.0