kernel/linux.git/fs/fuse, branch v6.18.33

fuse: avoid 0x10 fault in fuse_readahead when max_pages == 0

2026-05-23T11:07:16+00:00

[ Upstream commit 4ea907108a5c ("fuse: use iomap for readahead") ] The upstream fix is the iomap conversion in commit 4ea907108a5c ("fuse: use iomap for readahead"), which rewrote fuse_readahead() entirely and removed the buggy loop along with it. That refactor is too invasive to backport to the pre-iomap readahead path still used by 6.18.y (and earlier stable branches), so this is a minimal, equivalent fix to the same bug on those branches. When fc->max_read is smaller than PAGE_SIZE (common on aarch64 with 64K base pages if the FUSE server advertises a small max_read in INIT), max_pages = min(fc->max_pages, fc->max_read / PAGE_SIZE) is 0, so cur_pages is 0 on every outer iteration. fuse_io_alloc(NULL, 0) then calls fuse_folios_alloc(0, ...), which calls kzalloc(0, ...) and gets back ZERO_SIZE_PTR == (void *)16. The "if (!ia->ap.folios)" guard in fuse_io_alloc does not catch ZERO_SIZE_PTR, so fuse_io_alloc happily returns an ia whose ap.folios is 0x10. The inner "while (pages < cur_pages)" loop runs zero times, then fuse_send_readpages(ia, ...) dereferences ap->folios[0] in folio_pos(), faulting at virtual address 0x10: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010 fuse_readahead+0x14c/0x490 read_pages+0x80/0x318 page_cache_ra_unbounded+0x1c0/0x2b0 page_cache_ra_order+0xb8/0x368 page_cache_sync_ra+0x210/0x320 filemap_get_pages+0x290/0xdb0 generic_file_read_iter+0xd0/0x540 fuse_file_read_iter+0x8c/0x158 __arm64_sys_read+0x1a0/0x488 addr2line on the aarch64 vmlinux maps fuse_readahead+0x14c to fs/fuse/file.c:897 inlined into :999, i.e. "folio_pos(ap->folios[0])" inside fuse_send_readpages. The faulting instruction "ldr x8, [x8]" loads ap->folios[0]; ap->folios was previously loaded as 0x10 (ZERO_SIZE_PTR). Without this fix the function would also spin forever, since "nr_pages -= pages" makes no progress when pages stays 0; in practice the NULL deref masks the spin. Bail out of the outer loop if cur_pages is 0 -- there is no work we can issue via FUSE in this iteration, and remaining folios will be handled by read_pages() falling back to ->read_folio. Fixes: 3eab9d7bc2f4 ("fuse: convert readahead to use folios") Reported-by: Breno Leitao Reviewed-by: Joanne Koong Signed-off-by: Vlad Poenaru Signed-off-by: Sasha Levin

fuse: fuse_dev_ioctl_clone() should wait for device file to be initialized

2026-04-27T13:27:30+00:00

commit da6fcc6dbddbef80e603d2f0c1554a9f2ac03742 upstream. Use fuse_get_dev() not __fuse_get_dev() on the old fd, since in the case of synchronous INIT the caller will want to wait for the device file to be available for cloning, just like I/O wants to wait instead of returning an error. Fixes: dfb84c330794 ("fuse: allow synchronous FUSE_INIT") Cc: stable@vger.kernel.org # v6.18 Signed-off-by: Miklos Szeredi Signed-off-by: Greg Kroah-Hartman

fuse: quiet down complaints in fuse_conn_limit_write

2026-04-27T13:27:30+00:00

commit 129a45f9755a89f573c6a513a6b9e3d234ce89b0 upstream. gcc 15 complains about an uninitialized variable val that is passed by reference into fuse_conn_limit_write: control.c: In function ‘fuse_conn_congestion_threshold_write’: include/asm-generic/rwonce.h:55:37: warning: ‘val’ may be used uninitialized [-Wmaybe-uninitialized] 55 | *(volatile typeof(x) *)&(x) = (val); \ | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~ include/asm-generic/rwonce.h:61:9: note: in expansion of macro ‘__WRITE_ONCE’ 61 | __WRITE_ONCE(x, val); \ | ^~~~~~~~~~~~ control.c:178:9: note: in expansion of macro ‘WRITE_ONCE’ 178 | WRITE_ONCE(fc->congestion_threshold, val); | ^~~~~~~~~~ control.c:166:18: note: ‘val’ was declared here 166 | unsigned val; | ^~~ Unfortunately there's enough macro spew involved in kstrtoul_from_user that I think gcc gives up on its analysis and sprays the above warning. AFAICT it's not actually a bug, but we could just zero-initialize the variable to enable using -Wmaybe-uninitialized to find real problems. Previously we would use some weird uninitialized_var annotation to quiet down the warnings, so clearly this code has been like this for quite some time. Cc: stable@vger.kernel.org # v5.9 Fixes: 3f649ab728cda8 ("treewide: Remove uninitialized_var() usage") Signed-off-by: Darrick J. Wong Signed-off-by: Miklos Szeredi Signed-off-by: Greg Kroah-Hartman

fuse: Check for large folio with SPLICE_F_MOVE

2026-04-27T13:27:30+00:00

commit 59ba47b6be9cd0146ef9a55c6e32e337e11e7625 upstream. xfstest generic/074 and generic/075 complain result in kernel warning messages / page dumps. This is easily reproducible (on 6.19) with CONFIG_TRANSPARENT_HUGEPAGE_SHMEM_HUGE_ALWAYS=y CONFIG_TRANSPARENT_HUGEPAGE_TMPFS_HUGE_ALWAYS=y This just adds a test for large folios fuse_try_move_folio with the same page copy fallback, but to avoid the warnings from fuse_check_folio(). Cc: stable@vger.kernel.org Signed-off-by: Bernd Schubert Signed-off-by: Horst Birthelmer Signed-off-by: Miklos Szeredi Signed-off-by: Greg Kroah-Hartman

fuse: abort on fatal signal during sync init

2026-04-27T13:27:30+00:00

commit 204aa22a686bfee48daca7db620c1e017615f2ff upstream. When sync init is used and the server exits for some reason (error, crash) while processing FUSE_INIT, the filesystem creation will hang. The reason is that while all other threads will exit, the mounting thread (or process) will keep the device fd open, which will prevent an abort from happening. This is a regression from the async mount case, where the mount was done first, and the FUSE_INIT processing afterwards, in which case there's no such recursive syscall keeping the fd open. Fixes: dfb84c330794 ("fuse: allow synchronous FUSE_INIT") Cc: stable@vger.kernel.org # v6.18 Reviewed-by: Joanne Koong Reviewed-by: Bernd Schubert Reviewed-by: "Darrick J. Wong" Signed-off-by: Miklos Szeredi Signed-off-by: Greg Kroah-Hartman

fuse: reject oversized dirents in page cache

2026-04-27T13:27:30+00:00

commit 51a8de6c50bf947c8f534cd73da4c8f0a13e7bed upstream. fuse_add_dirent_to_cache() computes a serialized dirent size from the server-controlled namelen field and copies the dirent into a single page-cache page. The existing logic only checks whether the dirent fits in the remaining space of the current page and advances to a fresh page if not. It never checks whether the dirent itself exceeds PAGE_SIZE. As a result, a malicious FUSE server can return a dirent with namelen=4095, producing a serialized record size of 4120 bytes. On 4 KiB page systems this causes memcpy() to overflow the cache page by 24 bytes into the following kernel page. Reject dirents that cannot fit in a single page before copying them into the readdir cache. Fixes: 69e34551152a ("fuse: allow caching readdir") Cc: stable@vger.kernel.org # v6.16+ Assisted-by: Bynario AI Signed-off-by: Samuel Page Reported-by: Qi Tang Reported-by: Zijun Hu Signed-off-by: Miklos Szeredi Link: https://patch.msgid.link/20260420090139.662772-1-mszeredi@redhat.com Signed-off-by: Christian Brauner Signed-off-by: Greg Kroah-Hartman

writeback: don't block sync for filesystems with no data integrity guarantees

2026-04-02T11:23:20+00:00

commit 76f9377cd2ab7a9220c25d33940d9ca20d368172 upstream. Add a SB_I_NO_DATA_INTEGRITY superblock flag for filesystems that cannot guarantee data persistence on sync (eg fuse). For superblocks with this flag set, sync kicks off writeback of dirty inodes but does not wait for the flusher threads to complete the writeback. This replaces the per-inode AS_NO_DATA_INTEGRITY mapping flag added in commit f9a49aa302a0 ("fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()"). The flag belongs at the superblock level because data integrity is a filesystem-wide property, not a per-inode one. Having this flag at the superblock level also allows us to skip having to iterate every dirty inode in wait_sb_inodes() only to skip each inode individually. Prior to this commit, mappings with no data integrity guarantees skipped waiting on writeback completion but still waited on the flusher threads to finish initiating the writeback. Waiting on the flusher threads is unnecessary. This commit kicks off writeback but does not wait on the flusher threads. This change properly addresses a recent report [1] for a suspend-to-RAM hang seen on fuse-overlayfs that was caused by waiting on the flusher threads to finish: Workqueue: pm_fs_sync pm_fs_sync_work_fn Call Trace: __schedule+0x457/0x1720 schedule+0x27/0xd0 wb_wait_for_completion+0x97/0xe0 sync_inodes_sb+0xf8/0x2e0 __iterate_supers+0xdc/0x160 ksys_sync+0x43/0xb0 pm_fs_sync_work_fn+0x17/0xa0 process_one_work+0x193/0x350 worker_thread+0x1a1/0x310 kthread+0xfc/0x240 ret_from_fork+0x243/0x280 ret_from_fork_asm+0x1a/0x30 On fuse this is problematic because there are paths that may cause the flusher thread to block (eg if systemd freezes the user session cgroups first, which freezes the fuse daemon, before invoking the kernel suspend. The kernel suspend triggers ->write_node() which on fuse issues a synchronous setattr request, which cannot be processed since the daemon is frozen. Or if the daemon is buggy and cannot properly complete writeback, initiating writeback on a dirty folio already under writeback leads to writeback_get_folio() -> folio_prepare_writeback() -> unconditional wait on writeback to finish, which will cause a hang). This commit restores fuse to its prior behavior before tmp folios were removed, where sync was essentially a no-op. [1] https://lore.kernel.org/linux-fsdevel/CAJnrk1a-asuvfrbKXbEwwDSctvemF+6zfhdnuzO65Pt8HsFSRw@mail.gmail.com/T/#m632c4648e9cafc4239299887109ebd880ac6c5c1 Fixes: 0c58a97f919c ("fuse: remove tmp folio for writebacks and internal rb tree") Reported-by: John Cc: stable@vger.kernel.org Signed-off-by: Joanne Koong Link: https://patch.msgid.link/20260320005145.2483161-2-joannelkoong@gmail.com Reviewed-by: Jan Kara Reviewed-by: David Hildenbrand (Arm) Signed-off-by: Christian Brauner Signed-off-by: Greg Kroah-Hartman

fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

2026-01-30T09:32:15+00:00

commit f9a49aa302a05e91ca01f69031cb79a0ea33031f upstream. Above the while() loop in wait_sb_inodes(), we document that we must wait for all pages under writeback for data integrity. Consequently, if a mapping, like fuse, traditionally does not have data integrity semantics, there is no need to wait at all; we can simply skip these inodes. This restores fuse back to prior behavior where syncs are no-ops. This fixes a user regression where if a system is running a faulty fuse server that does not reply to issued write requests, this causes wait_sb_inodes() to wait forever. Link: https://lkml.kernel.org/r/20260105211737.4105620-2-joannelkoong@gmail.com Fixes: 0c58a97f919c ("fuse: remove tmp folio for writebacks and internal rb tree") Signed-off-by: Joanne Koong Reported-by: Athul Krishna Reported-by: J. Neuschäfer Reviewed-by: Bernd Schubert Tested-by: J. Neuschäfer Cc: Alexander Viro Cc: Bernd Schubert Cc: Bonaccorso Salvatore Cc: Christian Brauner Cc: David Hildenbrand Cc: Jan Kara Cc: "Liam R. Howlett" Cc: Lorenzo Stoakes Cc: "Matthew Wilcox (Oracle)" Cc: Michal Hocko Cc: Mike Rapoport Cc: Miklos Szeredi Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman

fuse: missing copy_finish in fuse-over-io-uring argument copies

2026-01-02T11:57:31+00:00

commit 6e0d7f7f4a43ac8868e98c87ecf48805aa8c24dd upstream. Fix a possible reference count leak of payload pages during fuse argument copies. [Joanne: simplified error cleanup] Fixes: c090c8abae4b ("fuse: Add io-uring sqe commit and fetch support") Cc: stable@vger.kernel.org # v6.14 Signed-off-by: Cheng Ding Signed-off-by: Bernd Schubert Reviewed-by: Joanne Koong Signed-off-by: Miklos Szeredi Signed-off-by: Greg Kroah-Hartman

fuse: fix readahead reclaim deadlock

2026-01-02T11:57:31+00:00

commit bd5603eaae0aabf527bfb3ce1bb07e979ce5bd50 upstream. Commit e26ee4efbc79 ("fuse: allocate ff->release_args only if release is needed") skips allocating ff->release_args if the server does not implement open. However in doing so, fuse_prepare_release() now skips grabbing the reference on the inode, which makes it possible for an inode to be evicted from the dcache while there are inflight readahead requests. This causes a deadlock if the server triggers reclaim while servicing the readahead request and reclaim attempts to evict the inode of the file being read ahead. Since the folio is locked during readahead, when reclaim evicts the fuse inode and fuse_evict_inode() attempts to remove all folios associated with the inode from the page cache (truncate_inode_pages_range()), reclaim will block forever waiting for the lock since readahead cannot relinquish the lock because it is itself blocked in reclaim: >>> stack_trace(1504735) folio_wait_bit_common (mm/filemap.c:1308:4) folio_lock (./include/linux/pagemap.h:1052:3) truncate_inode_pages_range (mm/truncate.c:336:10) fuse_evict_inode (fs/fuse/inode.c:161:2) evict (fs/inode.c:704:3) dentry_unlink_inode (fs/dcache.c:412:3) __dentry_kill (fs/dcache.c:615:3) shrink_kill (fs/dcache.c:1060:12) shrink_dentry_list (fs/dcache.c:1087:3) prune_dcache_sb (fs/dcache.c:1168:2) super_cache_scan (fs/super.c:221:10) do_shrink_slab (mm/shrinker.c:435:9) shrink_slab (mm/shrinker.c:626:10) shrink_node (mm/vmscan.c:5951:2) shrink_zones (mm/vmscan.c:6195:3) do_try_to_free_pages (mm/vmscan.c:6257:3) do_swap_page (mm/memory.c:4136:11) handle_pte_fault (mm/memory.c:5562:10) handle_mm_fault (mm/memory.c:5870:9) do_user_addr_fault (arch/x86/mm/fault.c:1338:10) handle_page_fault (arch/x86/mm/fault.c:1481:3) exc_page_fault (arch/x86/mm/fault.c:1539:2) asm_exc_page_fault+0x22/0x27 Fix this deadlock by allocating ff->release_args and grabbing the reference on the inode when preparing the file for release even if the server does not implement open. The inode reference will be dropped when the last reference on the fuse file is dropped (see fuse_file_put() -> fuse_release_end()). Fixes: e26ee4efbc79 ("fuse: allocate ff->release_args only if release is needed") Cc: stable@vger.kernel.org Signed-off-by: Joanne Koong Reported-by: Omar Sandoval Signed-off-by: Miklos Szeredi Signed-off-by: Greg Kroah-Hartman