SUNRPC: Track writers of the 'channel' file to improve cache_listeners_exist

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The sunrpc cache interface is susceptible to being fooled by a rogue
process just reading a 'channel' file.  If this happens the kernel
may think a valid daemon exists to service the cache when it does not.
For example, the following may fool the kernel:
cat /proc/net/rpc/auth.unix.gid/channel

Change the tracking of readers to writers when considering whether a
listener exists as all valid daemon processes either open a channel
file O_RDWR or O_WRONLY.  While this does not prevent a rogue process
from "stealing" a message from the kernel, it does at least improve
the kernels perception of whether a valid process servicing the cache
exists.

Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

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Dave Wysochanski 2019-07-26 18:33:01 -04:00 • committed by J. Bruce Fields

parent 609488bc97

commit 64a38e840c

2 changed files with 11 additions and 7 deletions

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6

include/linux/sunrpc/cache.h

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12

net/sunrpc/cache.c

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