varnish-bugs at varnish-cache
Jul 15, 2011, 4:02 AM
Post #1 of 3
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#962: Persistent storage don't work on Linux with Address space layout randomization
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#962: Persistent storage don't work on Linux with Address space layout
randomization
---------------------+------------------------------------------------------
Reporter: pmialon | Type: defect
Status: new | Priority: normal
Milestone: | Component: build
Version: 3.0.0 | Severity: normal
Keywords: |
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Debian Squeeze, Fedora 15 and RHEL 6 uses Adress space layout
randomization by default:
{{{
# sysctl kernel.randomize_va_space
kernel.randomize_va_space = 2
}}}
This breaks persistent storage:
{{{
# varnishd -d -a :80 -f /etc/varnish/default.vcl -s
persistent,/var/lib/varnish/instance/A.shm,10M
...
CHK(0x7fbfcc1330a0 SILO 0x7fbfcb0e1000 SILO) = 3
...
Platform: Linux,2.6.32-5-amd64,x86_64,-spersistent,-smalloc,-hcritbit
...
}}}
By disabling ASLR (sysctl kernel.randomize_va_space=0), it works again.
In source:bin/varnishd/storage_persistent_mgt.c, smp_mgt_init():
{{{
sc->base = mmap(NULL, sc->mediasize, PROT_READ|PROT_WRITE,
MAP_NOCORE | MAP_NOSYNC | MAP_SHARED, sc->fd, 0);
...
smp_def_sign(sc, &sc->idn, 0, "SILO");
...
i = smp_valid_silo(sc);
}}}
mmap(2) may return a random address. This address is stored in sc->idn->ss
and written to the mmap()'d file in smp_reset_sign():
{{{
ctx->ss->mapped = (uintptr_t)ctx->ss;
}}}
This is ok with the very first run because the file is created and the
mmap address stored. But with following run, smp_valid_silo() calls
smp_chk_sign() (source:bin/varnishd/storage_persistent_subr.c) which
compares addresses from mmap(2) and the file:
{{{
if ((uintptr_t)ctx->ss != ctx->ss->mapped)
r = 3
}}}
This causes the silo to be reset.
--
Ticket URL: <http://www.varnish-cache.org/trac/ticket/962>
Varnish <http://varnish-cache.org/>
The Varnish HTTP Accelerator
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