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authorDave Wysochanski <dwysocha@redhat.com>2019-07-26 18:33:01 -0400
committerJ. Bruce Fields <bfields@redhat.com>2019-07-30 11:55:53 -0400
commit64a38e840ce5940253208eaba40265c73decc4ee (patch)
treed4f490e97e05dcacfb8906222c32d7f57bae8e6a /net/sunrpc
parent609488bc979f99f805f34e9a32c1e3b71179d10b (diff)
SUNRPC: Track writers of the 'channel' file to improve cache_listeners_exist
The sunrpc cache interface is susceptible to being fooled by a rogue process just reading a 'channel' file. If this happens the kernel may think a valid daemon exists to service the cache when it does not. For example, the following may fool the kernel: cat /proc/net/rpc/auth.unix.gid/channel Change the tracking of readers to writers when considering whether a listener exists as all valid daemon processes either open a channel file O_RDWR or O_WRONLY. While this does not prevent a rogue process from "stealing" a message from the kernel, it does at least improve the kernels perception of whether a valid process servicing the cache exists. Signed-off-by: Dave Wysochanski <dwysocha@redhat.com> Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Diffstat (limited to 'net/sunrpc')
-rw-r--r--net/sunrpc/cache.c12
1 files changed, 8 insertions, 4 deletions
diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 6f1528f271ee..a6a6190ad37a 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -373,7 +373,7 @@ void sunrpc_init_cache_detail(struct cache_detail *cd)
spin_lock(&cache_list_lock);
cd->nextcheck = 0;
cd->entries = 0;
- atomic_set(&cd->readers, 0);
+ atomic_set(&cd->writers, 0);
cd->last_close = 0;
cd->last_warn = -1;
list_add(&cd->others, &cache_list);
@@ -1029,11 +1029,13 @@ static int cache_open(struct inode *inode, struct file *filp,
}
rp->offset = 0;
rp->q.reader = 1;
- atomic_inc(&cd->readers);
+
spin_lock(&queue_lock);
list_add(&rp->q.list, &cd->queue);
spin_unlock(&queue_lock);
}
+ if (filp->f_mode & FMODE_WRITE)
+ atomic_inc(&cd->writers);
filp->private_data = rp;
return 0;
}
@@ -1062,8 +1064,10 @@ static int cache_release(struct inode *inode, struct file *filp,
filp->private_data = NULL;
kfree(rp);
+ }
+ if (filp->f_mode & FMODE_WRITE) {
+ atomic_dec(&cd->writers);
cd->last_close = seconds_since_boot();
- atomic_dec(&cd->readers);
}
module_put(cd->owner);
return 0;
@@ -1171,7 +1175,7 @@ static void warn_no_listener(struct cache_detail *detail)
static bool cache_listeners_exist(struct cache_detail *detail)
{
- if (atomic_read(&detail->readers))
+ if (atomic_read(&detail->writers))
return true;
if (detail->last_close == 0)
/* This cache was never opened */