CVE-2025-38523 Information

Aug 17, 2025 cve

Description

In the Linux kernel the following vulnerability has been resolved:

cifs: Fix the smbd_response slab to allow usercopy

The handling of received data in the smbdirect client code involves using copy_to_iter() to copy data from the smbd_reponse struct’s packet trailer to a folioq buffer provided by netfslib that encapsulates a chunk of pagecache.

If however CONFIG_HARDENED_USERCOPY=y this will result in the checks then performed in copy_to_iter() oopsing with something like the following:

CIFS: Attempting to mount //172.31.9.1/test CIFS: VFS: RDMA transport established usercopy: Kernel memory exposure attempt detected from SLUB object ‘smbd_response_0000000091e24ea1’ (offset 81 size 63)! ————[ cut here ]———— kernel BUG at mm/usercopy.c:102! … RIP: 0010:usercopy_abort+0x6c/0x80 … Call Trace: __check_heap_object+0xe3/0x120 __check_object_size+0x4dc/0x6d0 smbd_recv+0x77f/0xfe0 [cifs] cifs_readv_from_socket+0x276/0x8f0 [cifs] cifs_read_from_socket+0xcd/0x120 [cifs] cifs_demultiplex_thread+0x7e9/0x2d50 [cifs] kthread+0x396/0x830 ret_from_fork+0x2b8/0x3b0 ret_from_fork_asm+0x1a/0x30

The problem is that the smbd_response slab’s packet field isn’t marked as being permitted for usercopy.

Fix this by passing parameters to kmem_slab_create() to indicate that copy_to_iter() is permitted from the packet region of the smbd_response slab objects less the header space.

Reference

https://git.kernel.org/stable/c/43e7e284fc77b710d899569360ea46fa3374ae22 https://git.kernel.org/stable/c/87dcc7e33fc3dcb8ed32333cec016528b5bb6ce4 https://git.kernel.org/stable/c/f0dd353d47f7051afa98c6c60c7486831eb1a410

CNNVD-202508-1942 (Published: 2025-08-16)

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