kernel/linux.git/fs/9p, branch v6.6.145

9p: skip nlink update in cacheless mode to fix WARN_ON

2026-07-24T14:03:36+00:00

commit 574aa0b4799470ac814479f1138d19efe6262255 upstream. v9fs_dec_count() unconditionally calls drop_nlink() on regular files, even when the inode's nlink is already zero. In cacheless mode the client refetches inode metadata from the server (the source of truth) on every operation, so by the time v9fs_remove() returns, the locally cached nlink may already reflect the post-unlink value: 1. Client initiates unlink, server processes it and sets nlink to 0 2. Client refetches inode metadata (nlink=0) before unlink returns 3. Client's v9fs_remove() completes successfully 4. Client calls v9fs_dec_count() which calls drop_nlink() on nlink=0 This race is easily triggered under heavy unlink workloads, such as stress-ng's unlink stressor, producing the following warning: WARNING: fs/inode.c:417 at drop_nlink+0x4c/0xc8 Call trace: drop_nlink+0x4c/0xc8 v9fs_remove+0x1e0/0x250 [9p] v9fs_vfs_unlink+0x20/0x38 [9p] vfs_unlink+0x13c/0x258 ... In cacheless mode the server is authoritative and the inode is on its way out, so locally adjusting nlink buys nothing. Skip v9fs_dec_count() entirely when neither CACHE_META nor CACHE_LOOSE is set, which both avoids the warning and removes a class of nlink races (two concurrent unlinkers observing nlink > 0 and both calling drop_nlink()) that an nlink == 0 guard alone would only narrow rather than close. Fixes: ac89b2ef9b55 ("9p: don't maintain dir i_nlink if the exported fs doesn't either") Cc: stable@vger.kernel.org Suggested-by: Dominique Martinet Signed-off-by: Breno Leitao Message-ID: <20260421-9p-v2-1-48762d294fad@debian.org> Signed-off-by: Dominique Martinet Signed-off-by: Greg Kroah-Hartman

9p: fix cache/debug options printing in v9fs_show_options

2026-01-11T14:21:36+00:00

[ Upstream commit f0445613314f474c1a0ec6fa8a5cd153a618f1b6 ] commit 4eb3117888a92 changed the cache= option to accept either string shortcuts or bitfield values. It also changed /proc/mounts to emit the option as the hexadecimal numeric value rather than the shortcut string. However, by printing "cache=%x" without the leading 0x, shortcuts such as "cache=loose" will emit "cache=f" and 'f' is not a string that is parseable by kstrtoint(), so remounting may fail if a remount with "cache=f" is attempted. debug=%x has had the same problem since options have been displayed in c4fac9100456 ("9p: Implement show_options") Fix these by adding the 0x prefix to the hexadecimal value shown in /proc/mounts. Fixes: 4eb3117888a92 ("fs/9p: Rework cache modes and add new options to Documentation") Signed-off-by: Eric Sandeen Message-ID: <54b93378-dcf1-4b04-922d-c8b4393da299@redhat.com> [Dominique: use %#x at Al Viro's suggestion, also handle debug] Tested-by: Remi Pommarel Signed-off-by: Dominique Martinet Signed-off-by: Sasha Levin

fs/9p: Don't open remote file with APPEND mode when writeback cache is used

2026-01-11T14:21:20+00:00

[ Upstream commit a63dd8fd137933551bfd9aeeeaa942f04c7aad65 ] When page cache is used, writebacks are done on a page granularity, and it is expected that the underlying filesystem (such as v9fs) should respect the write position. However, currently v9fs will passthrough O_APPEND to the server even on cached mode. This causes data corruption if a sync or fstat gets between two writes to the same file. This patch removes the APPEND flag from the open request we send to the server when writeback caching is involved. I believe keeping server-side APPEND is probably fine for uncached mode (even if two fds are opened, one without O_APPEND and one with it, this should still be fine since they would use separate fid for the writes). Signed-off-by: Tingmao Wang Fixes: 4eb3117888a9 ("fs/9p: Rework cache modes and add new options to Documentation") Message-ID: <20251102235631.8724-1-m@maowtm.org> Signed-off-by: Dominique Martinet Signed-off-by: Sasha Levin

9p: sysfs_init: don't hardcode error to ENOMEM

2025-11-24T09:29:48+00:00

[ Upstream commit 528f218b31aac4bbfc58914d43766a22ab545d48 ] v9fs_sysfs_init() always returned -ENOMEM on failure; return the actual sysfs_create_group() error instead. Signed-off-by: Randall P. Embry Message-ID: <20250926-v9fs_misc-v1-3-a8b3907fc04d@codewreck.org> Signed-off-by: Dominique Martinet Signed-off-by: Sasha Levin

9p: fix /sys/fs/9p/caches overwriting itself

2025-11-24T09:29:48+00:00

[ Upstream commit 86db0c32f16c5538ddb740f54669ace8f3a1f3d7 ] caches_show() overwrote its buffer on each iteration, so only the last cache tag was visible in sysfs output. Properly append with snprintf(buf + count, …). Signed-off-by: Randall P. Embry Message-ID: <20250926-v9fs_misc-v1-2-a8b3907fc04d@codewreck.org> Signed-off-by: Dominique Martinet Signed-off-by: Sasha Levin

fs/9p: fix uninitialized values during inode evict

2024-11-22T14:38:37+00:00

[ Upstream commit 6630036b7c228f57c7893ee0403e92c2db2cd21d ] If an iget fails due to not being able to retrieve information from the server then the inode structure is only partially initialized. When the inode gets evicted, references to uninitialized structures (like fscache cookies) were being made. This patch checks for a bad_inode before doing anything other than clearing the inode from the cache. Since the inode is bad, it shouldn't have any state associated with it that needs to be written back (and there really isn't a way to complete those anyways). Reported-by: syzbot+eb83fe1cce5833cd66a0@syzkaller.appspotmail.com Signed-off-by: Eric Van Hensbergen Signed-off-by: Sasha Levin [Xiangyu: CVE-2024-36923 Minor conflict resolution ] Signed-off-by: Xiangyu Chen Signed-off-by: Greg Kroah-Hartman

9p: v9fs_fid_find: also lookup by inode if not found dentry

2024-11-17T14:08:55+00:00

[ Upstream commit 38d222b3163f7b7d737e5d999ffc890a12870e36 ] It's possible for v9fs_fid_find "find by dentry" branch to not turn up anything despite having an entry set (because e.g. uid doesn't match), in which case the calling code will generally make an extra lookup to the server. In this case we might have had better luck looking by inode, so fall back to look up by inode if we have one and the lookup by dentry failed. Message-Id: <20240523210024.1214386-1-asmadeus@codewreck.org> Reviewed-by: Christian Schoenebeck Signed-off-by: Dominique Martinet Signed-off-by: Sasha Levin

9p: add missing locking around taking dentry fid list

2024-06-16T11:47:37+00:00

commit c898afdc15645efb555acb6d85b484eb40a45409 upstream. Fix a use-after-free on dentry's d_fsdata fid list when a thread looks up a fid through dentry while another thread unlinks it: UAF thread: refcount_t: addition on 0; use-after-free. p9_fid_get linux/./include/net/9p/client.h:262 v9fs_fid_find+0x236/0x280 linux/fs/9p/fid.c:129 v9fs_fid_lookup_with_uid linux/fs/9p/fid.c:181 v9fs_fid_lookup+0xbf/0xc20 linux/fs/9p/fid.c:314 v9fs_vfs_getattr_dotl+0xf9/0x360 linux/fs/9p/vfs_inode_dotl.c:400 vfs_statx+0xdd/0x4d0 linux/fs/stat.c:248 Freed by: p9_fid_destroy (inlined) p9_client_clunk+0xb0/0xe0 linux/net/9p/client.c:1456 p9_fid_put linux/./include/net/9p/client.h:278 v9fs_dentry_release+0xb5/0x140 linux/fs/9p/vfs_dentry.c:55 v9fs_remove+0x38f/0x620 linux/fs/9p/vfs_inode.c:518 vfs_unlink+0x29a/0x810 linux/fs/namei.c:4335 The problem is that d_fsdata was not accessed under d_lock, because d_release() normally is only called once the dentry is otherwise no longer accessible but since we also call it explicitly in v9fs_remove that lock is required: move the hlist out of the dentry under lock then unref its fids once they are no longer accessible. Fixes: 154372e67d40 ("fs/9p: fix create-unlink-getattr idiom") Cc: stable@vger.kernel.org Reported-by: Meysam Firouzi Reported-by: Amirmohammad Eftekhar Reviewed-by: Christian Schoenebeck Message-ID: <20240521122947.1080227-1-asmadeus@codewreck.org> Signed-off-by: Dominique Martinet Signed-off-by: Greg Kroah-Hartman

fs/9p: drop inodes immediately on non-.L too

2024-05-17T10:02:19+00:00

[ Upstream commit 7fd524b9bd1be210fe79035800f4bd78a41b349f ] Signed-off-by: Joakim Sindholt Signed-off-by: Eric Van Hensbergen Signed-off-by: Sasha Levin

9p: explicitly deny setlease attempts

2024-05-17T10:02:18+00:00

[ Upstream commit 7a84602297d36617dbdadeba55a2567031e5165b ] 9p is a remote network protocol, and it doesn't support asynchronous notifications from the server. Ensure that we don't hand out any leases since we can't guarantee they'll be broken when a file's contents change. Signed-off-by: Jeff Layton Signed-off-by: Eric Van Hensbergen Signed-off-by: Sasha Levin