CVE-2023-53593

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

cifs: Release folio lock on fscache read hit.

Under the current code, when cifs_readpage_worker is called, the call contract is that the callee should unlock the page. This is documented in the read_folio section of Documentation/filesystems/vfs.rst as:

The filesystem should unlock the folio once the read has completed, whether it was successful or not.

Without this change, when fscache is in use and cache hit occurs during a read, the page lock is leaked, producing the following stack on subsequent reads (via mmap) to the page:

$ cat /proc/3890/task/12864/stack [<0>] folio_wait_bit_common+0x124/0x350 [<0>] filemap_read_folio+0xad/0xf0 [<0>] filemap_fault+0x8b1/0xab0 [<0>] __do_fault+0x39/0x150 [<0>] do_fault+0x25c/0x3e0 [<0>] __handle_mm_fault+0x6ca/0xc70 [<0>] handle_mm_fault+0xe9/0x350 [<0>] do_user_addr_fault+0x225/0x6c0 [<0>] exc_page_fault+0x84/0x1b0 [<0>] asm_exc_page_fault+0x27/0x30

This requires a reboot to resolve; it is a deadlock.

Note however that the call to cifs_readpage_from_fscache does mark the page clean, but does not free the folio lock. This happens in __cifs_readpage_from_fscache on success. Releasing the lock at that point however is not appropriate as cifs_readahead also calls cifs_readpage_from_fscache and does unconditionally release the lock after its return. This change therefore effectively makes cifs_readpage_worker work like cifs_readahead.

Affected Software

References

• https://git.kernel.org/stable/c/4259dd534245579c966c53c15187cc8e9461d6e9
• https://git.kernel.org/stable/c/5a87735675147f848445f05fd1f06168188f91af
• https://git.kernel.org/stable/c/69513dd669e243928f7450893190915a88f84a2b
• https://git.kernel.org/stable/c/6e74926ede96470be84e66a1c576982fe4f8ea79
• https://git.kernel.org/stable/c/7a9fb689c1a1dc373887621a3bfa3810df0abde4
• https://git.kernel.org/stable/c/961f7ce16223aee2db583a43877d84e6d1f2b857
• https://git.kernel.org/stable/c/9e725386d4262ef23ae51993f04602bc535b5be2
• https://git.kernel.org/stable/c/c3ac8323f2f5b50e32681c254b8318f7fa2dc3f4