diff options
| author | Dave Wysochanski <dwysocha@redhat.com> | 2019-07-27 00:33:01 +0200 |
|---|---|---|
| committer | J. Bruce Fields <bfields@redhat.com> | 2019-07-30 17:55:53 +0200 |
| commit | 64a38e840ce5940253208eaba40265c73decc4ee (patch) | |
| tree | d4f490e97e05dcacfb8906222c32d7f57bae8e6a /net | |
| parent | Linux 5.3-rc2 (diff) | |
| download | linux-64a38e840ce5940253208eaba40265c73decc4ee.tar.xz linux-64a38e840ce5940253208eaba40265c73decc4ee.zip | |
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')
| -rw-r--r-- | net/sunrpc/cache.c | 12 |
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 */ |