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author | NeilBrown <neilb@suse.de> | 2010-11-16 16:55:19 +1100 |
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committer | J. Bruce Fields <bfields@redhat.com> | 2010-12-07 20:39:55 -0500 |
commit | ed2849d3ecfa339435818eeff28f6c3424300cec (patch) | |
tree | 2fbef743779156c2c96afecd8311ff8488a90121 /fs/nfsd | |
parent | cf7d7e5a1980d1116ee152d25dac382b112b9c17 (diff) | |
download | kernel_samsung_tuna-ed2849d3ecfa339435818eeff28f6c3424300cec.zip kernel_samsung_tuna-ed2849d3ecfa339435818eeff28f6c3424300cec.tar.gz kernel_samsung_tuna-ed2849d3ecfa339435818eeff28f6c3424300cec.tar.bz2 |
sunrpc: prevent use-after-free on clearing XPT_BUSY
When an xprt is created, it has a refcount of 1, and XPT_BUSY is set.
The refcount is *not* owned by the thread that created the xprt
(as is clear from the fact that creators never put the reference).
Rather, it is owned by the absence of XPT_DEAD. Once XPT_DEAD is set,
(And XPT_BUSY is clear) that initial reference is dropped and the xprt
can be freed.
So when a creator clears XPT_BUSY it is dropping its only reference and
so must not touch the xprt again.
However svc_recv, after calling ->xpo_accept (and so getting an XPT_BUSY
reference on a new xprt), calls svc_xprt_recieved. This clears
XPT_BUSY and then svc_xprt_enqueue - this last without owning a reference.
This is dangerous and has been seen to leave svc_xprt_enqueue working
with an xprt containing garbage.
So we need to hold an extra counted reference over that call to
svc_xprt_received.
For safety, any time we clear XPT_BUSY and then use the xprt again, we
first get a reference, and the put it again afterwards.
Note that svc_close_all does not need this extra protection as there are
no threads running, and the final free can only be called asynchronously
from such a thread.
Signed-off-by: NeilBrown <neilb@suse.de>
Cc: stable@kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Diffstat (limited to 'fs/nfsd')
0 files changed, 0 insertions, 0 deletions