From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 C96B827470; Tue, 15 Jul 2025 13:57:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752587851; cv=none; b=H29dIFPBIixJ0ssEuSuh9OFj1XF4oc8h5jLEloaJEUWU+gASzbRUaSmmwPsba71ylS59DjozGp3Ww8DHDAhvm5qcf9dYD3u2R3AWCTyRJLcvvXazJoGJeFqoW9a7xYNUvmCOV2AKx2nxTbWpFYjg8b/rLtFwpL7CkMoKP8EyoB8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752587851; c=relaxed/simple; bh=Aov9zJ7acWMx7zoK3s8v37x0ypdEHPNvBu4RCADqodI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=FaaTC1DcHerZL5RLKm3goeAM2noKGUo88HqEWmbkku+b0jYoAPRoMDOpTWnhCCDwRk4AarRfsiCbzLDtGwq3NdDfKPM5ikWLPWvSIU6MQsYG88VjRItzPBuXBgybcmuvHD00B8r2FSOycswjfXRlzQ2AtmbL4LNVg+8FOuNnct4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=IgVsvoNT; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="IgVsvoNT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5CB95C4CEF1; Tue, 15 Jul 2025 13:57:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1752587851; bh=Aov9zJ7acWMx7zoK3s8v37x0ypdEHPNvBu4RCADqodI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=IgVsvoNTPEIpzQ5WnWcGT7n9v/rKN7dN1UqLRqGDG76256dHQ8N1RdjTQDnnF036Q mhamtZN9UMcOgsYSqDp9wvJ2jKpTLmtGiVhRcmuthn2KkWS1L58tO3VT6UqCTvkw3A RpSOmyfCHTI5mxTz5Csk6eEWsgKhj8VjgbynCZZg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, NeilBrown , Christian Brauner , NeilBrown , Al Viro , Sasha Levin Subject: [PATCH 5.10 136/208] fix proc_sys_compare() handling of in-lookup dentries Date: Tue, 15 Jul 2025 15:14:05 +0200 Message-ID: <20250715130816.380856795@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250715130810.830580412@linuxfoundation.org> References: <20250715130810.830580412@linuxfoundation.org> User-Agent: quilt/0.68 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 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Al Viro [ Upstream commit b969f9614885c20f903e1d1f9445611daf161d6d ] There's one case where ->d_compare() can be called for an in-lookup dentry; usually that's nothing special from ->d_compare() point of view, but... proc_sys_compare() is weird. The thing is, /proc/sys subdirectories can look differently for different processes. Up to and including having the same name resolve to different dentries - all of them hashed. The way it's done is ->d_compare() refusing to admit a match unless this dentry is supposed to be visible to this caller. The information needed to discriminate between them is stored in inode; it is set during proc_sys_lookup() and until it's done d_splice_alias() we really can't tell who should that dentry be visible for. Normally there's no negative dentries in /proc/sys; we can run into a dying dentry in RCU dcache lookup, but those can be safely rejected. However, ->d_compare() is also called for in-lookup dentries, before they get positive - or hashed, for that matter. In case of match we will wait until dentry leaves in-lookup state and repeat ->d_compare() afterwards. In other words, the right behaviour is to treat the name match as sufficient for in-lookup dentries; if dentry is not for us, we'll see that when we recheck once proc_sys_lookup() is done with it. While we are at it, fix the misspelled READ_ONCE and WRITE_ONCE there. Fixes: d9171b934526 ("parallel lookups machinery, part 4 (and last)") Reported-by: NeilBrown Reviewed-by: Christian Brauner Reviewed-by: NeilBrown Signed-off-by: Al Viro Signed-off-by: Sasha Levin --- fs/proc/inode.c | 2 +- fs/proc/proc_sysctl.c | 18 +++++++++++------- 2 files changed, 12 insertions(+), 8 deletions(-) diff --git a/fs/proc/inode.c b/fs/proc/inode.c index ba35ffc426eac..269a14a50d8b0 100644 --- a/fs/proc/inode.c +++ b/fs/proc/inode.c @@ -54,7 +54,7 @@ static void proc_evict_inode(struct inode *inode) head = ei->sysctl; if (head) { - RCU_INIT_POINTER(ei->sysctl, NULL); + WRITE_ONCE(ei->sysctl, NULL); proc_sys_evict_inode(inode, head); } } diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c index f5c9677353354..78bd606314281 100644 --- a/fs/proc/proc_sysctl.c +++ b/fs/proc/proc_sysctl.c @@ -909,17 +909,21 @@ static int proc_sys_compare(const struct dentry *dentry, struct ctl_table_header *head; struct inode *inode; - /* Although proc doesn't have negative dentries, rcu-walk means - * that inode here can be NULL */ - /* AV: can it, indeed? */ - inode = d_inode_rcu(dentry); - if (!inode) - return 1; if (name->len != len) return 1; if (memcmp(name->name, str, len)) return 1; - head = rcu_dereference(PROC_I(inode)->sysctl); + + // false positive is fine here - we'll recheck anyway + if (d_in_lookup(dentry)) + return 0; + + inode = d_inode_rcu(dentry); + // we just might have run into dentry in the middle of __dentry_kill() + if (!inode) + return 1; + + head = READ_ONCE(PROC_I(inode)->sysctl); return !head || !sysctl_is_seen(head); } -- 2.39.5