CVE-2026-90042

In the Linux kernel, the following vulnerability has been resolved:

ceph: properly decrypt filenames in vmalloc() buffers

The fscrypt subsystem uses the scatterlist crypto API, inheriting its

requirement that any buffers are in the linear mapping region. However,

the messenger client uses kvmalloc() to create buffers for messages,

which will occasionally place those buffers in the vmalloc() region when

physical memory fragmentation doesn't permit a large enough kmalloc().

The various callers of cephfnameto_usr() directly pass (slices of) raw

messages from the MDS without considering that the messages may be in

vmalloc() buffers, resulting in oopses especially on non-x86 platforms

(see 'Closes:' for more details and a reproducer).

Make cephfnameto_usr() explicitly tolerant of vmalloc()-allocated

fname->ctext, fname->name, and/or oname->name buffers, using tname

(which, when non-null, must be a linear address; when null, is briefly

allocated as necessary) as a bounce buffer to avoid passing any

inappropriate addresses to fscryptfnamedisktousr().

Additionally change parsereplyinfo_readdir() -- the only function to

supply its own tname -- to follow the new "tname must never come from

vmalloc()" rule by passing NULL when the message is not in the linear

region. Though this causes a per-dentry kmalloc()+kfree(), this overhead

exists only when processing the minority of messages that spill into

vmalloc(). My (crude) testing puts this at only about 1 in 8,000 readdir

messages. Still, if the overhead proves unreasonable in the future, it

is easy enough to mitigate: a future change could allocate a bounce

buffer in parsereplyinfo_readdir() and use that as tname instead.