Linux kernel CIFS SMB2 async write server repick misaccounting
CVE-2024-42256 Published on August 8, 2024
cifs: Fix server re-repick on subrequest retry
In the Linux kernel, the following vulnerability has been resolved:
cifs: Fix server re-repick on subrequest retry
When a subrequest is marked for needing retry, netfs will call
cifs_prepare_write() which will make cifs repick the server for the op
before renegotiating credits; it then calls cifs_issue_write() which
invokes smb2_async_writev() - which re-repicks the server.
If a different server is then selected, this causes the increment of
server->in_flight to happen against one record and the decrement to happen
against another, leading to misaccounting.
Fix this by just removing the repick code in smb2_async_writev(). As this
is only called from netfslib-driven code, cifs_prepare_write() should
always have been called first, and so server should never be NULL and the
preparatory step is repeated in the event that we do a retry.
The problem manifests as a warning looking something like:
WARNING: CPU: 4 PID: 72896 at fs/smb/client/smb2ops.c:97 smb2_add_credits+0x3f0/0x9e0 [cifs]
...
RIP: 0010:smb2_add_credits+0x3f0/0x9e0 [cifs]
...
smb2_writev_callback+0x334/0x560 [cifs]
cifs_demultiplex_thread+0x77a/0x11b0 [cifs]
kthread+0x187/0x1d0
ret_from_fork+0x34/0x60
ret_from_fork_asm+0x1a/0x30
Which may be triggered by a number of different xfstests running against an
Azure server in multichannel mode. generic/249 seems the most repeatable,
but generic/215, generic/249 and generic/308 may also show it.
Products Associated with CVE-2024-42256
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Affected Versions
Linux:- Version 3ee1a1fc39819906f04d6c62c180e760cd3a689d and below b1d0a566769b6fb3795b5289fc1daf9e0638d97a is affected.
- Version 3ee1a1fc39819906f04d6c62c180e760cd3a689d and below de40579b903883274fe203865f29d66b168b7236 is affected.
- Version 6.10 is affected.
- Before 6.10 is unaffected.
- Version 6.10.1, <= 6.10.* is unaffected.
- Version 6.11, <= * is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.