PT-2026-43919 · Linux · Linux

Published

2026-05-27

·

Updated

2026-05-27

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CVE-2026-46052

CVSS v3.1

7.5

High

VectorAV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
In the Linux kernel, the following vulnerability has been resolved:
ceph: only d add() negative dentries when they are unhashed
Ceph can call d add(dentry, NULL) on a negative dentry that is already present in the primary dcache hash.
In the current VFS that is not safe. d add() goes through d add() to d rehash(), which unconditionally reinserts dentry->d hash into the hlist bl bucket. If the dentry is already hashed, reinserting the same node can corrupt the bucket, including creating a self-loop. Once that happens, d lookup() can spin forever in the hlist bl walk, typically looping only on the d name.hash mismatch check and eventually triggering RCU stall reports like this one:
rcu: INFO: rcu sched self-detected stall on CPU rcu: 87-....: (2100 ticks this GP) idle=3a4c/1/0x4000000000000000 softirq=25003319/25003319 fqs=829 rcu: (t=2101 jiffies g=79058445 q=698988 ncpus=192) CPU: 87 UID: 2952868916 PID: 3933303 Comm: php-cgi8.3 Not tainted 6.18.17-i1-amd #950 NONE Hardware name: Dell Inc. PowerEdge R7615/0G9DHV, BIOS 1.6.6 09/22/2023 RIP: 0010: d lookup+0x46/0xb0 Code: c1 e8 07 48 8d 04 c2 48 8b 00 49 89 fc 49 89 f5 48 89 c3 48 83 e3 fe 48 83 f8 01 77 0f eb 2d 0f 1f 44 00 00 48 8b 1b 48 85 db <74> 20 39 6b 18 75 f3 48 8d 7b 78 e8 ba 85 d0 00 4c 39 63 10 74 1f RSP: 0018:ff745a70c8253898 EFLAGS: 00000282 RAX: ff26e470054cb208 RBX: ff26e470054cb208 RCX: 000000006e958966 RDX: ff26e48267340000 RSI: ff745a70c82539b0 RDI: ff26e458f74655c0 RBP: 000000006e958966 R08: 0000000000000180 R09: 9cd08d909b919a89 R10: ff26e458f74655c0 R11: 0000000000000000 R12: ff26e458f74655c0 R13: ff745a70c82539b0 R14: d0d0d0d0d0d0d0d0 R15: 2f2f2f2f2f2f2f2f FS: 00007f5770896980(0000) GS:ff26e482c5d88000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f5764de50c0 CR3: 000000a72abb5001 CR4: 0000000000771ef0 PKRU: 55555554 Call Trace: lookup fast+0x9f/0x100 walk component+0x1f/0x150 link path walk+0x20e/0x3d0 path lookupat+0x68/0x180 filename lookup+0xdc/0x1e0 vfs statx+0x6c/0x140 vfs fstatat+0x67/0xa0 do sys newfstatat+0x24/0x60 do syscall 64+0x6a/0x230 entry SYSCALL 64 after hwframe+0x76/0x7e
This is reachable with reused cached negative dentries. A Ceph lookup or atomic open can be handed a negative dentry that is already hashed, and fs/ceph/dir.c then hits one of two paths that incorrectly assume "negative" also means "unhashed":
  • ceph finish lookup(): MDS reply is -ENOENT with no trace -> d add(dentry, NULL)
  • ceph lookup(): local ENOENT fast path for a complete directory with shared caps -> d add(dentry, NULL)
Both paths can therefore re-add an already-hashed negative dentry.
Ceph already uses the correct pattern elsewhere: ceph fill trace() only calls d add(dn, NULL) for a negative null-dentry reply when d unhashed(dn) is true.
Fix both fs/ceph/dir.c sites the same way: only call d add() for a negative dentry when it is actually unhashed. If the negative dentry is already hashed, leave it in place and reuse it as-is.
This preserves the existing behavior for unhashed dentries while avoiding d hash list corruption for reused hashed negatives.

Fix

Related Identifiers

CVE-2026-46052

Affected Products

Linux