From e586e86add4e4bf42f7af5b6d570fbe9b49fc415 Mon Sep 17 00:00:00 2001
From: Andrew Deason <adeason@sinenomine.net>
Date: Thu, 21 Mar 2019 15:24:06 -0500
Subject: [PATCH] LINUX: Avoid lookup ENOENT on fatal signals
Various Linux kernel operations on various Linux kernel versions can
fail if the current process has a pending fatal signal (i.e. SIGKILL),
including reads and writes to our local disk cache. Depending on what
and when something fails because of this, some parts of libafs throw
an ENOENT error, which may propagate up to callers, and be returned
from afs_lookup(). Notably this can happen via some functions in
src/dir/dir.c, and previously was possible with some code paths before
they were fixed by commit 2aa4cb04 (afs: Stop abusing ENOENT).
For the most part, the exact error given to the userspace caller
doesn't matter, since the process will die as soon as we return to
userspace. However, for ENOENT errors specifically for lookups, we
interpret this to mean that the target filename is known to not exist,
and so we create a negative dentry for that name, which is cached.
Future lookups for that filename will then result in ENOENT before any
AFS functions are called.
The lingering abuses of the ENOENT error code should be removed from
libafs entirely, but as an extra layer of safety, we can just avoid
returning ENOENT from lookups if the current process has a pending
fatal signal. So to do that, change all afs_lookup() callers in
src/afs/LINUX to translate ENOENT to EINTR if we have a pending fatal
signal. If fatal_signal_pending() is not available, then we don't do
this translation.
FIXES 134904
Reviewed-on: https://gerrit.openafs.org/13530
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 8b6ae2893b517bd4e008cae94acff70abe4d2227)
Change-Id: I8bf1b24c97ed74b0b457d79f48b2f40416c1d37e
Reviewed-on: https://gerrit.openafs.org/13542
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Marcio Brito Barbosa <mbarbosa@sinenomine.net>
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
---
src/afs/LINUX/osi_vnodeops.c | 13 +++++++++++++
src/cf/linux-kernel-func.m4 | 3 +++
2 files changed, 16 insertions(+), 0 deletions(-)
diff --git a/src/afs/LINUX/osi_vnodeops.c b/src/afs/LINUX/osi_vnodeops.c
index 966e98a..a9f18a7 100644
--- a/src/afs/LINUX/osi_vnodeops.c
+++ b/src/afs/LINUX/osi_vnodeops.c
@@ -1135,6 +1135,17 @@ parent_vcache_dv(struct inode *inode, cred_t *credp)
return hgetlo(pvcp->f.m.DataVersion);
}
+static inline int
+filter_enoent(int code)
+{
+#ifdef HAVE_LINUX_FATAL_SIGNAL_PENDING
+ if (code == ENOENT && fatal_signal_pending(current)) {
+ return EINTR;
+ }
+#endif
+ return code;
+}
+
#ifndef D_SPLICE_ALIAS_RACE
static inline void dentry_race_lock(void) {}
@@ -1304,6 +1315,7 @@ afs_linux_dentry_revalidate(struct dentry *dp, int flags)
credp = crref();
}
code = afs_lookup(pvcp, (char *)dp->d_name.name, &tvc, credp);
+ code = filter_enoent(code);
if (code) {
/* We couldn't perform the lookup, so we're not okay. */
@@ -1595,6 +1607,7 @@ afs_linux_lookup(struct inode *dip, struct dentry *dp)
AFS_GLOCK();
code = afs_lookup(VTOAFS(dip), (char *)comp, &vcp, credp);
+ code = filter_enoent(code);
if (code == ENOENT) {
/* It's ok for the file to not be found. That's noted by the caller by
* seeing that the dp->d_inode field is NULL (set by d_splice_alias or
diff --git a/src/cf/linux-kernel-func.m4 b/src/cf/linux-kernel-func.m4
index 34c5fa4..597730f 100644
--- a/src/cf/linux-kernel-func.m4
+++ b/src/cf/linux-kernel-func.m4
@@ -42,6 +42,9 @@ AC_CHECK_LINUX_FUNC([d_make_root],
AC_CHECK_LINUX_FUNC([do_sync_read],
[#include <linux/fs.h>],
[do_sync_read(NULL, NULL, 0, NULL);])
+AC_CHECK_LINUX_FUNC([fatal_signal_pending],
+ [#include <linux/sched.h>],
+ [fatal_signal_pending(NULL);])
AC_CHECK_LINUX_FUNC([file_dentry],
[#include <linux/fs.h>],
[struct file *f; file_dentry(f);])
--
1.7.1
