fscache_create_volume_work() uses wake_up_bit() to wake up the processes
which are waiting for the completion of volume creation. According to
comments in wake_up_bit() and waitqueue_active(), an extra smp_mb() is
needed to guarantee the memory order between FSCACHE_VOLUME_CREATING
flag and waitqueue_active() before invoking wake_up_bit().
Fixing it by using clear_and_wake_up_bit() to add the missing memory
barrier.
Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20230113115211.2895845-3-houtao@huaweicloud.com/ # v3
The freeing of relinquished volume will wake up the pending volume
acquisition by using wake_up_bit(), however it is mismatched with
wait_var_event() used in fscache_wait_on_volume_collision() and it will
never wake up the waiter in the wait-queue because these two functions
operate on different wait-queues.
According to the implementation in fscache_wait_on_volume_collision(),
if the wake-up of pending acquisition is delayed longer than 20 seconds
(e.g., due to the delay of on-demand fd closing), the first
wait_var_event_timeout() will timeout and the following wait_var_event()
will hang forever as shown below:
FS-Cache: Potential volume collision new=00000024 old=00000022
......
INFO: task mount:1148 blocked for more than 122 seconds.
Not tainted 6.1.0-rc6+ #1
task:mount state:D stack:0 pid:1148 ppid:1
Call Trace:
<TASK>
__schedule+0x2f6/0xb80
schedule+0x67/0xe0
fscache_wait_on_volume_collision.cold+0x80/0x82
__fscache_acquire_volume+0x40d/0x4e0
erofs_fscache_register_volume+0x51/0xe0 [erofs]
erofs_fscache_register_fs+0x19c/0x240 [erofs]
erofs_fc_fill_super+0x746/0xaf0 [erofs]
vfs_get_super+0x7d/0x100
get_tree_nodev+0x16/0x20
erofs_fc_get_tree+0x20/0x30 [erofs]
vfs_get_tree+0x24/0xb0
path_mount+0x2fa/0xa90
do_mount+0x7c/0xa0
__x64_sys_mount+0x8b/0xe0
do_syscall_64+0x30/0x60
entry_SYSCALL_64_after_hwframe+0x46/0xb0
Considering that wake_up_bit() is more selective, so fix it by using
wait_on_bit() instead of wait_var_event() to wait for the freeing of
relinquished volume. In addition because waitqueue_active() is used in
wake_up_bit() and clear_bit() doesn't imply any memory barrier, use
clear_and_wake_up_bit() to add the missing memory barrier between
cursor->flags and waitqueue_active().
Fixes: 62ab633523 ("fscache: Implement volume registration")
Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20230113115211.2895845-2-houtao@huaweicloud.com/ # v3
The type of a->key[0] is char in fscache_volume_same(). If the length
of cache volume key is greater than 127, the value of a->key[0] is less
than 0. In this case, klen becomes much larger than 255 after type
conversion, because the type of klen is size_t. As a result, memcmp()
is read out of bounds.
This causes a slab-out-of-bounds Read in __fscache_acquire_volume(), as
reported by Syzbot.
Fix this by changing the type of the stored key to "u8 *" rather than
"char *" (it isn't a simple string anyway). Also put in a check that
the volume name doesn't exceed NAME_MAX.
BUG: KASAN: slab-out-of-bounds in memcmp+0x16f/0x1c0 lib/string.c:757
Read of size 8 at addr ffff888016f3aa90 by task syz-executor344/3613
Call Trace:
memcmp+0x16f/0x1c0 lib/string.c:757
memcmp include/linux/fortify-string.h:420 [inline]
fscache_volume_same fs/fscache/volume.c:133 [inline]
fscache_hash_volume fs/fscache/volume.c:171 [inline]
__fscache_acquire_volume+0x76c/0x1080 fs/fscache/volume.c:328
fscache_acquire_volume include/linux/fscache.h:204 [inline]
v9fs_cache_session_get_cookie+0x143/0x240 fs/9p/cache.c:34
v9fs_session_init+0x1166/0x1810 fs/9p/v9fs.c:473
v9fs_mount+0xba/0xc90 fs/9p/vfs_super.c:126
legacy_get_tree+0x105/0x220 fs/fs_context.c:610
vfs_get_tree+0x89/0x2f0 fs/super.c:1530
do_new_mount fs/namespace.c:3040 [inline]
path_mount+0x1326/0x1e20 fs/namespace.c:3370
do_mount fs/namespace.c:3383 [inline]
__do_sys_mount fs/namespace.c:3591 [inline]
__se_sys_mount fs/namespace.c:3568 [inline]
__x64_sys_mount+0x27f/0x300 fs/namespace.c:3568
Fixes: 62ab633523 ("fscache: Implement volume registration")
Reported-by: syzbot+a76f6a6e524cf2080aa3@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Zhang Peng <zhangpeng362@huawei.com>
Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
cc: Dominique Martinet <asmadeus@codewreck.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: v9fs-developer@lists.sourceforge.net
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/Y3OH+Dmi0QIOK18n@codewreck.org/ # Zhang Peng's v1 fix
Link: https://lore.kernel.org/r/20221115140447.2971680-1-zhangpeng362@huawei.com/ # Zhang Peng's v2 fix
Link: https://lore.kernel.org/r/166869954095.3793579.8500020902371015443.stgit@warthog.procyon.org.uk/ # v1
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Add functions to the fscache API to allow volumes to be acquired and
relinquished by the network filesystem. A volume is an index of data
storage cache objects. A volume is represented by a volume cookie in the
API. A filesystem would typically create a volume for a superblock and
then create per-inode cookies within it.
To request a volume, the filesystem calls:
struct fscache_volume *
fscache_acquire_volume(const char *volume_key,
const char *cache_name,
const void *coherency_data,
size_t coherency_len)
The volume_key is a printable string used to match the volume in the cache.
It should not contain any '/' characters. For AFS, for example, this would
be "afs,<cellname>,<volume_id>", e.g. "afs,example.com,523001".
The cache_name can be NULL, but if not it should be a string indicating the
name of the cache to use if there's more than one available.
The coherency data, if given, is an arbitrarily-sized blob that's attached
to the volume and is compared when the volume is looked up. If it doesn't
match, the old volume is judged to be out of date and it and everything
within it is discarded.
Acquiring a volume twice concurrently is disallowed, though the function
will wait if an old volume cookie is being relinquishing.
When a network filesystem has finished with a volume, it should return the
volume cookie by calling:
void
fscache_relinquish_volume(struct fscache_volume *volume,
const void *coherency_data,
bool invalidate)
If invalidate is true, the entire volume will be discarded; if false, the
volume will be synced and the coherency data will be updated.
Changes
=======
ver #4:
- Removed an extraneous param from kdoc on fscache_relinquish_volume()[3].
ver #3:
- fscache_hash()'s size parameter is now in bytes. Use __le32 as the unit
to round up to.
- When comparing cookies, simply see if the attributes are the same rather
than subtracting them to produce a strcmp-style return[2].
- Make the coherency data an arbitrary blob rather than a u64, but don't
store it for the moment.
ver #2:
- Fix error check[1].
- Make a fscache_acquire_volume() return errors, including EBUSY if a
conflicting volume cookie already exists. No error is printed now -
that's left to the netfs.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/20211203095608.GC2480@kili/ [1]
Link: https://lore.kernel.org/r/CAHk-=whtkzB446+hX0zdLsdcUJsJ=8_-0S1mE_R+YurThfUbLA@mail.gmail.com/ [2]
Link: https://lore.kernel.org/r/20211220224646.30e8205c@canb.auug.org.au/ [3]
Link: https://lore.kernel.org/r/163819588944.215744.1629085755564865996.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906890630.143852.13972180614535611154.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967086836.1823006.8191672796841981763.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021495816.640689.4403156093668590217.stgit@warthog.procyon.org.uk/ # v4
