kernel/linux.git/fs/afs/volume.c, branch v6.7

afs: Fix use-after-free due to get/remove race in volume tree

2023-12-21T18:16:07+00:00

When an afs_volume struct is put, its refcount is reduced to 0 before the cell->volume_lock is taken and the volume removed from the cell->volumes tree. Unfortunately, this means that the lookup code can race and see a volume with a zero ref in the tree, resulting in a use-after-free: refcount_t: addition on 0; use-after-free. WARNING: CPU: 3 PID: 130782 at lib/refcount.c:25 refcount_warn_saturate+0x7a/0xda ... RIP: 0010:refcount_warn_saturate+0x7a/0xda ... Call Trace: afs_get_volume+0x3d/0x55 afs_create_volume+0x126/0x1de afs_validate_fc+0xfe/0x130 afs_get_tree+0x20/0x2e5 vfs_get_tree+0x1d/0xc9 do_new_mount+0x13b/0x22e do_mount+0x5d/0x8a __do_sys_mount+0x100/0x12a do_syscall_64+0x3a/0x94 entry_SYSCALL_64_after_hwframe+0x62/0x6a Fix this by: (1) When putting, use a flag to indicate if the volume has been removed from the tree and skip the rb_erase if it has. (2) When looking up, use a conditional ref increment and if it fails because the refcount is 0, replace the node in the tree and set the removal flag. Fixes: 20325960f875 ("afs: Reorganise volume and server trees to be rooted on the cell") Signed-off-by: David Howells Reviewed-by: Jeffrey Altman cc: Marc Dionne cc: linux-afs@lists.infradead.org Signed-off-by: Linus Torvalds

afs: remove variable nr_servers

2022-12-22T11:40:35+00:00

Variable nr_servers is no longer being used, the last reference to it was removed in commit 45df8462730d ("afs: Fix server list handling") so clean up the code by removing it. Signed-off-by: Colin Ian King Signed-off-by: David Howells cc: Marc Dionne cc: linux-afs@lists.infradead.org Link: https://lore.kernel.org/r/20221020173923.21342-1-colin.i.king@gmail.com/

afs: Use refcount_t rather than atomic_t

2022-08-02T17:10:11+00:00

Use refcount_t rather than atomic_t in afs to make use of the count checking facilities provided. Signed-off-by: David Howells Reviewed-by: Marc Dionne cc: linux-afs@lists.infradead.org Link: https://lore.kernel.org/r/165911277768.3745403.423349776836296452.stgit@warthog.procyon.org.uk/ # v1

afs: Fix some checker issues

2022-06-10T19:55:21+00:00

Remove an unused global variable and make another static as reported by make C=1. Signed-off-by: David Howells cc: linux-afs@lists.infradead.org

afs: Convert afs to use the new fscache API

2022-01-07T13:44:47+00:00

Change the afs filesystem to support the new afs driver. The following changes have been made: (1) The fscache_netfs struct is no more, and there's no need to register the filesystem as a whole. There's also no longer a cell cookie. (2) The volume cookie is now an fscache_volume cookie, allocated with fscache_acquire_volume(). This function takes three parameters: a string representing the "volume" in the index, a string naming the cache to use (or NULL) and a u64 that conveys coherency metadata for the volume. For afs, I've made it render the volume name string as: "afs,," and the coherency data is currently 0. (3) The fscache_cookie_def is no more and needed information is passed directly to fscache_acquire_cookie(). The cache no longer calls back into the filesystem, but rather metadata changes are indicated at other times. fscache_acquire_cookie() is passed the same keying and coherency information as before, except that these are now stored in big endian form instead of cpu endian. This makes the cache more copyable. (4) fscache_use_cookie() and fscache_unuse_cookie() are called when a file is opened or closed to prevent a cache file from being culled and to keep resources to hand that are needed to do I/O. fscache_use_cookie() is given an indication if the cache is likely to be modified locally (e.g. the file is open for writing). fscache_unuse_cookie() is given a coherency update if we had the file open for writing and will update that. (5) fscache_invalidate() is now given uptodate auxiliary data and a file size. It can also take a flag to indicate if this was due to a DIO write. This is wrapped into afs_fscache_invalidate() now for convenience. (6) fscache_resize() now gets called from the finalisation of afs_setattr(), and afs_setattr() does use/unuse of the cookie around the call to support this. (7) fscache_note_page_release() is called from afs_release_page(). (8) Use a killable wait in nfs_vm_page_mkwrite() when waiting for PG_fscache to be cleared. Render the parts of the cookie key for an afs inode cookie as big endian. Changes ======= ver #2: - Use gfpflags_allow_blocking() rather than using flag directly. - fscache_acquire_volume() now returns errors. Signed-off-by: David Howells Acked-by: Jeff Layton Tested-by: kafs-testing@auristor.com cc: Marc Dionne cc: linux-afs@lists.infradead.org cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/163819661382.215744.1485608824741611837.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906970002.143852.17678518584089878259.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967174665.1823006.1301789965454084220.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/164021568841.640689.6684240152253400380.stgit@warthog.procyon.org.uk/ # v4

afs: Add tracing for cell refcount and active user count

2020-10-16T13:39:21+00:00

Add a tracepoint to log the cell refcount and active user count and pass in a reason code through various functions that manipulate these counters. Additionally, a helper function, afs_see_cell(), is provided to log interesting places that deal with a cell without actually doing any accounting directly. Signed-off-by: David Howells

afs: Fix cell refcounting by splitting the usage counter

2020-10-16T13:38:22+00:00

Management of the lifetime of afs_cell struct has some problems due to the usage counter being used to determine whether objects of that type are in use in addition to whether anyone might be interested in the structure. This is made trickier by cell objects being cached for a period of time in case they're quickly reused as they hold the result of a setup process that may be slow (DNS lookups, AFS RPC ops). Problems include the cached root volume from alias resolution pinning its parent cell record, rmmod occasionally hanging and occasionally producing assertion failures. Fix this by splitting the count of active users from the struct reference count. Things then work as follows: (1) The cell cache keeps +1 on the cell's activity count and this has to be dropped before the cell can be removed. afs_manage_cell() tries to exchange the 1 to a 0 with the cells_lock write-locked, and if successful, the record is removed from the net->cells. (2) One struct ref is 'owned' by the activity count. That is put when the active count is reduced to 0 (final_destruction label). (3) A ref can be held on a cell whilst it is queued for management on a work queue without confusing the active count. afs_queue_cell() is added to wrap this. (4) The queue's ref is dropped at the end of the management. This is split out into a separate function, afs_manage_cell_work(). (5) The root volume record is put after a cell is removed (at the final_destruction label) rather then in the RCU destruction routine. (6) Volumes hold struct refs, but aren't active users. (7) Both counts are displayed in /proc/net/afs/cells. There are some management function changes: (*) afs_put_cell() now just decrements the refcount and triggers the RCU destruction if it becomes 0. It no longer sets a timer to have the manager do this. (*) afs_use_cell() and afs_unuse_cell() are added to increase and decrease the active count. afs_unuse_cell() sets the management timer. (*) afs_queue_cell() is added to queue a cell with approprate refs. There are also some other fixes: (*) Don't let /proc/net/afs/cells access a cell's vllist if it's NULL. (*) Make sure that candidate cells in lookups are properly destroyed rather than being simply kfree'd. This ensures the bits it points to are destroyed also. (*) afs_dec_cells_outstanding() is now called in cell destruction rather than at "final_destruction". This ensures that cell->net is still valid to the end of the destructor. (*) As a consequence of the previous two changes, move the increment of net->cells_outstanding that was at the point of insertion into the tree to the allocation routine to correctly balance things. Fixes: 989782dcdc91 ("afs: Overhaul cell database management") Signed-off-by: David Howells

afs: Reorganise volume and server trees to be rooted on the cell

2020-06-04T14:37:57+00:00

Reorganise afs_volume objects such that they're in a tree keyed on volume ID, rooted at on an afs_cell object rather than being in multiple trees, each of which is rooted on an afs_server object. afs_server structs become per-cell and acquire a pointer to the cell. The process of breaking a callback then starts with finding the server by its network address, following that to the cell and then looking up each volume ID in the volume tree. This is simpler than the afs_vol_interest/afs_cb_interest N:M mapping web and allows those structs and the code for maintaining them to be simplified or removed. It does make a couple of things a bit more tricky, though: (1) Operations now start with a volume, not a server, so there can be more than one answer as to whether or not the server we'll end up using supports the FS.InlineBulkStatus RPC. (2) CB RPC operations that specify the server UUID. There's still a tree of servers by UUID on the afs_net struct, but the UUIDs in it aren't guaranteed unique. Signed-off-by: David Howells

afs: Add a tracepoint to track the lifetime of the afs_volume struct

2020-06-04T14:37:57+00:00

Add a tracepoint to track the lifetime of the afs_volume struct. Signed-off-by: David Howells

afs: Detect cell aliases 1 - Cells with root volumes

2020-06-04T14:37:57+00:00

Put in the first phase of cell alias detection. This part handles alias detection for cells that have root.cell volumes (which is expected to be likely). When a cell becomes newly active, it is probed for its root.cell volume, and if it has one, this volume is compared against other root.cell volumes to find out if the list of fileserver UUIDs have any in common - and if that's the case, do the address lists of those fileservers have any addresses in common. If they do, the new cell is adjudged to be an alias of the old cell and the old cell is used instead. Comparing is aided by the server list in struct afs_server_list being sorted in UUID order and the addresses in the fileserver address lists being sorted in address order. The cell then retains the afs_volume object for the root.cell volume, even if it's not mounted for future alias checking. This necessary because: (1) Whilst fileservers have UUIDs that are meant to be globally unique, in practice they are not because cells get cloned without changing the UUIDs - so afs_server records need to be per cell. (2) Sometimes the DNS is used to make cell aliases - but if we don't know they're the same, we may end up with multiple superblocks and multiple afs_server records for the same thing, impairing our ability to deliver callback notifications of third party changes (3) The fileserver RPC API doesn't contain the cell name, so it can't tell us which cell it's notifying and can't see that a change made to to one cell should notify the same client that's also accessed as the other cell. Reported-by: Jeffrey Altman Signed-off-by: David Howells